Industrial Safety and Health Management,5th Ed,Asfahl ,Solution Manual

CHAPTER 1

SOLUTIONS TO END-OF-CHAPTER EXERCISES

1.1.

Some standards are frequently cited because these standards cover (1) areas in which industries are having difficulty complying, or (2) areas in which enforcement agencies are giving a great deal of attention, or both.

1.2.

Many aspects about the standards might be useful. The text emphasizes the importance of the "why" behind the standards that do exist.

1.3.

No. It is an unattainable goal. Such a strategy fails to recognize the need for discrimination among hazards to be corrected.

1.4.

(1) Hazards that are physically infeasible to correct. (2) Hazards that are physically feasible, but are economically infeasible, to correct. (3) Hazards that are physically feasible and economically feasible to correct.

1.5.

(1) Causes other more serious hazards to be overlooked while reacting to less serious ones. (2) Deteriorates credibility with top management.

1.6.

A safety hazard is acute, causes or threatens to cause injuries, and is usually more obvious than a health hazard. A health hazard is chronic, causes or threatens to cause illness in the long run, and is usually more subtle than a safety hazard.

1.7.

Some example safety hazards: unguarded belts, pulleys, gears, saws, and punch presses; fires; explosions; open platforms; defective ladders; welding near open flammable or combustible materials; overloaded or defective cranes, hoists, or slings; ungrounded electrical equipment; exposed live electrical conductors. Some example health hazards: coal dust, cotton dust, chronic loud noise, welding fumes, asbestos, vinyl chloride, lead fumes, mercury, manganese, cadmium.

1.8.

Some valid examples are spray paint, coal dust, benzene, and carbon disulfide.

1.9.

Some valid examples are noise, welding, and radiation.

1.10.

Health hazards are usually more subtle than safety hazards; the industrial hygienist must look for "unseen" hazards.

1.11.

Safety hazards may appear more grave, but there are probably many health hazard-related illnesses and deaths which are not documented.

1.12.

Work training, statistics, job placement, industrial relations.

1.13.

A comprehensive safety and health program involves engineering, and placement of the function within the personnel department may restrict authority too much.

1.14.

This places the Safety and Health Manager in an adversarial position with enforcement officials.

1.15.

CPSC concentrates on the responsibility of the manufacturers of the machines and equipment, whereas OSHA concentrates on the responsibility of the employer who places the equipment into use in the workplace.

1.16.

(NSC) National Safety Council

1.17.

ANSI (American National Standards Institute) Prepares voluntary standards for occupational safety and health among other types of standards. OSHA adopted many ANSI standards early on, invoking its temporary right to promulgate "national consensus standards."

1.18.

OSHA is concerned with hazardous exposures to workers, i.e. worker safety and health. EPA is concerned with hazardous exposures to the public, particularly as these hazards affect the earth, water, and atmosphere. Many safety and health hazards inside the plant and outside are the same, or are caused by the same chemical agents or physical factors. Thus a firm's compliance with both EPA and OSHA regulations are often

the responsibility of the same individual. 1.19.

1-800-35-NIOSH; the agency that responds is, obviously, NIOSH, the National Institute for Occupational Safety and Health.

1.20.

Passage of The Occupational Safety and Health Act of 1970, which created the Occupational Safety and Health Administration (OSHA).

1.21.

Prior to passage of the OSHA law occupational health seemed remote and not of a great deal of concern. Plant nurses were concerned with first aid and physical examinations. After OSHA, occupational disease prevention rose in importance.

RESEARCH EXERCISES 1.22.

www.nsc.org Resources include library resources, safety training, professional development seminars, videos. www.asse.org Resources include training, professional development, standards, publications, annual conference and exposition, government affairs information, and a national registry of safety engineers in various areas of specialty. www.aiha.org Resources include employment services, laboratory services, education, annual meetings, a consultant registry, and training support materials, such as power point lecture outlines on various topics related to industrial hygiene.

1.23.

The best websites for checking these requirements are the boards that set the requirements. Following are the respective websites for the certifications: CSP: www.bcsp.com/ CIH: www.abih.org

1.24.

An Internet search on the term ―Certified Industrial Hygienist‖ will return thousands of sites, including many individuals who hold the designation, plus job opportunities for CIHs, plus lists of qualified CIHs.

1.25.

An Internet search on the term ―Certified Safety Professional‖ will return thousands of sites, including many individuals who hold the designation, plus job opportunities for CSPs.

1.26.

This data may be difficult to find on the Internet. It was once available from the Board of Certified Safety Professionals. Suggestion: search the BCSP website.

1.27.

The OSHA website is dynamic, so changes can be expected from time to time. As of this writing, there was a section on the main page entitled "Cooperative Programs" and under this heading a link entitled "VPP." The "VPP" link opened a variety of descriptive material, including a link to "An Overview of VPP."

1.28.

News Releases are an excellent source of current information on OSHA's website. They can be found under the general heading "Newsroom." Recent news releases are searchable through the webpage search capability on the main page. Older news releases are archived and can be searched by keyword also. This is a good place to find the original announcement of standards in the federal register. Then using the date of publication from the announcement, you can go to the Federal Register (also available on the OSHA website) and find the original promulgation of the standard. The promulgation will include a lot of background information in the "preamble."

1.29.

Health hazards are usually due to unseen agents that must be identified with scientific instruments. It is even difficult to determine and quantify the degree of hazard, because health hazards have subtle effects on the body. Another difficulty is long latency periods. A worker's health is sometimes significantly and irreversibly affected, but the effects do not appear until many years later. Safety hazards, by comparison, have dramatic and instantaneous effects that can easily

be seen.

CHAPTER 2

SOLUTIONS TO END-OF-CHAPTER EXERCISES

2.1.

The achievement of worker safety lies principally in the hands of the workers themselves and their direct supervisors; thus it is principally a line function. Safety and health managers, however, are staff positions.

2.2.

Acting as a facilitator in assisting, motivating, and advising the line function in achieving worker safety and health.

2.3.

They too often are such emotional crusaders for the cause that they lose their credibility and with it their eligibility to be considered a "manager."

2.4.

That safety must be achieved by line personnel facilitated by the staff function.

2.5.

Go to top management to re-determine its level of commitment to safety and health.

2.6.

The workers compensation system is a state, not federal system. The system is nearly 100 years old; the first workers compensation laws were introduced into state legislatures in 1909.

2.7.

The ostensible purpose is to protect the worker by providing statutory compensation levels to be paid by the employer for various injuries that may be incurred by the worker. An ulterior feature is immunity from additional liability for the employer, except where "gross negligence" can be proven.

2.8.

Management contends that some risk is inescapable in any line of work. Therefore, their answer to the question is no. The worker bears some of the risk in return for his/her pay for the job.

2.9.

The employer or the employer's insurance carrier.

2.10.

An industrial safety consultant employed by an insurance company. consultant's objective is to keep claims low among clients of his insurance company.

2.11.

A standardized recordkeeping system for industrial safety established by the National Safety Council and later superseded by OSHA's system of recordkeeping.

2.12.

Differences in recordkeeping requirements for OSHA and its predecessor Z16.1 system. Also other variations in conditions, such as employment levels and recession cycles.

2.13.

The "lost workdays" method would not reveal some very serious accidents, especially fatalities, that do not cause a loss of a workday.

2.14.

One that is work related and requires medical treatment.

2.15.

25 x 200,000 300 x 40 x 50

2.16.

The injury/illness incidence rate computation prescribed by OSHA relates to 200,000 work-hours (roughly one year for a 100-employee firm), whereas the traditional frequency rate relates to 1,000,000 work-hours (roughly one year for a 500 employee firm). Also the OSHA injury/illness incidence rate applies to all work-related injuries/illnesses which require medical treatment, whereas the traditional frequency rate related only to "lost-time" cases.

2.17.

Frequency measures the numbers of cases per standard quantity of workhours. Severity measures the total impact of cases in terms of total "lost workdays" per standard quantity of workhours. Seriousness is the ratio of severity to frequency and measures the average seriousness of all cases. All three are obsolete terms now.

2.18.

OSHA Form 300a, the annual "Summary of Work-Related Injuries and Illnesses" must be posted on February 1 each year and remain posted until April 30.

=

The

25 = 8.33 3

2.19.

For general records: 5 years (Chapter 5 will reveal longer retention requirements for certain records.)

2.20.

Yes; they can help to discover hazards, but they can also dilute responsibility for workplace safety and health and can degenerate into spy parties. Without adequate orientation, safety and health committees can often become unreasonable.

2.21.

Direct costs are the "tip of the iceberg" compared to indirect costs.

2.22.

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

Costs of wages paid for time lost by workers who were not injured. Cost of damage to material or equipment. Cost of wages paid for time lost by the injured worker. Extra cost of overtime work necessitated by the accident. Cost of wages paid supervisors for time required for activities necessitated by the accident. Wage cost caused by decreased output of injured worker after return to work. Cost of learning period of new worker. Uninsured medical cost borne by the company. Cost of time spent by higher supervision and clerical workers. Miscellaneous costs such as public liability claims, rental equipment, and lost sales.

2.23.

Noninjury accidents are usually caused by the same types of conditions and practices that result in injury accidents.

2.24.

First-line supervisors

2.25.

A six-month work period = 1000 hours. (a) General injury/illness rate = 18 x 200,000 = 72 50 x 1000 (b) Traditional frequency rate = 4 x 1,000,000 = 80 50 x 1000 (c) Comparing with general statistics for the Year 2000 in Figure 2.2, this appears to be a very dangerous industry. For the Year 2000, the total incidence rate (lost workday cases + cases without lost workdays) was 6.1, compared to this firm's general rate of 72. This firm is approximately six times as dangerous as the "average firm" in the private sector. Even compared to the most dangerous industries in Figure 2.2 ("transportation by air" and "transportation equipment") this firm is more than four times as dangerous. The "traditional frequency rate" of 80 is not comparable to Table 2.2 because it is based on a factor of 1,000,000, not 200,000. Had the "lost workday cases" rate been calculated using the 200,000 factor, the result would have been 16. This would compare with a general "private sector" rate of 3.0 for the Year 2000. So, by the "lost workday cases" criterion also, this is a very dangerous firm.

2.26.

Total injury incidence rate

LWDI 2.27.

(a) Total incidence rate

=

(2 + 1) x 200,000 -----------------------25 x 2000

=

300/25 = 12

=

1 x 200,000 25 x 2000

=

(3+1+1+1+1) x 200,000 62 x 2000

=

=

4

11.29

(b) (According to current OSHA recordkeeping policy, count calendar days, not just workweek days, i.e. 7 days/wk, not 5 days/wk) Number-of-lost-workdays rate

=

(7+7+42) x 200,000 62 x 2000

=

90.3

(c)

LWDI

=

1 x 200,000 62 x 2000

=

1.6

(excludes illnesses and all fatalities) 2.28.

The 12 first-aid cases are non-recordable. The two illnesses do not enter into the calculation of the LWDI, but the lost-time injuries would. Therefore, the LWDI would be calculated as: LWDI =

3 x 200,000 135 x (4/12) x 2000

= 6.67 for the 4-month period

Since 6.67 > 3.6, this would indicate that improvement is needed to meet the objective. However, if no more lost time injuries occurred for the year (an unlikely outcome): LWDI = 3 x 200,000 = 300 135 x 2000 135

= 2.22

and the objective LWDI of 3.6 would easily be met. 2.29.

The classification of the 12 accident files in this case study is subject to some variation due to individual judgment. This analysis will assume the following classification: Columns on the OSHA 300 Log

File 1 2 3 4 5 6 7 8 9 10 11 12

G

H

I

J

K

L

M1

M2

M3

M4

M5

not recordable X

14

X

not recordable X

28

7

X X

X X X

not recordable X

X

X

14

X

not recordable X Column Totals: (a) LWDI

X 4

1

0

3

42 70

3 38

X X 4

2

0

= 1 x 200,000 = 1 = .11 900 x 2000 9

(The LWDI excludes fatalities, excludes illnesses, and includes all "lost-time" injuries, including those injuries in which the worker has "restricted work activity days," i.e. is temporarily transferred to another job, even if there are no days away from work.) Total Injury rate = (4 - 1) x 200,000 = 3 = .33 (excluding fatalities) 900 x 2000 9 Total Illness rate = (2+0+1+1) x 200,000 = 4 = .44 900 x 2000 9 Fatality rate

=

1 x 200,000 = 1 = .11 900 x 2000 9

Number-of-lost-workdays rate

=

(70 + 38) x 200,000 900 x 2000

=

108/9

=

12

1

1

Specific hazard incidence rate (fractures)

= (1 + 1) x 200,000 900 x 2000 = 2/9 = .22

(b) Comparing National Safety Council Statistics for 2000 (see Figure 2.2 of the text): Total incidence (including fatalities) .89 1000 ppm, PEL is exceeded.

9.32. Percent PPM

Tube 5H Lower Upper .05% 8.0% 500 80000

Range Lower .002% 20

Tube 5M Upper .36% 3600

Tube 5M is more sensitive. 9.33.

Ceiling (MAC) concentration for hydrogen sulfide (H2S) is 20 ppm (from Appendix A.2 of the text). Four tubes in the table encompass the 20 ppm MAC. They are 4H, 4M, 4L, and 4LL. Tube 4LL covers the narrowest range (.25 ppm - 60 ppm).

9.34.

From Table A.1 of the text, the PEL (TWA) for isopropyl acetate is 250 ppm. The AL = 1/2 PEL = 125 ppm Detector tube range: 0.05% to 0.75% converted to ppm: Detector tube range: 500 ppm to 7500 ppm The detector tube is of insufficient sensitivity to be useful as a detector of concentrations near the PEL or AL.

9.35.

1 micrometer = 10-6 meters; 1 cm = 10-2 meters; 1 cm = 10-4 micrometers Diameter in centimeters = 17 x 10-4 = 0.0017 cm Diameter in inches = .0017cm/2.54 cm/in = .00067 in. The particle would be classified as dust.

9.36.

Contaminant

Conc

Isopropyl ether Ethyl benzene Chlorobenzene Chlorobromomethane

200 50

PEL 40 25

500 200

AL 100 75

250 100

50 37.5

Taken separately none of the contaminants exceed either their respective PEL's or AL's. When considered together, however, the following formula is used for mixtures: Em = (200/500) + (40/100) + (25/75) + (50/200) = .4 + .4 + .33 + .25 = 1.38 Since 1.38 > 1 and 1.38 > 0.5, the concentrations exceed both the PEL

and the AL, respectively. 9.37.

On the surface it appears that the new solvent will help matters by reducing the solvent vapor release by 20%. However, 20% is only a modest improvement, and a more knowledgeable assessment would include a comparison of the PELs for the two solvents under consideration. The old solvent, Stoddard solvent, is listed in the OSHA list for air contaminant PELs as a TWA of 500 ppm (see Appendix A.1). The new solvent, perchloroethylene is listed in Appendix A.1 with a reference to Appendix A.2. Earlier editions of the Appendix have recognized "perchloroehtylene" and "tetrachloroethylene" as synonyms. Tetrachloroethylene is found in Appendix A.2 to have a TWA PEL of 100 ppm and a MAC of 200 ppm. Therefore perchloroethylene is much more tightly controlled as a more hazardous substance than Stoddard solvent. The advantage of the modest reduction in solvent vapors is more than offset by the fact that the new solvent is much more dangerous, five times as dangerous as indicated by the ratio of PELs. It would be more difficult to control the new solvent to levels within the PEL and AL. The consultant should point this out to the process engineer and caution against making the process change.

9.38. Substance

Morning Exposure (4 hrs)

Afternoon Exposure (4 hrs)

Ci 8-hr TWA

Li OSHA PEL*

Ci/Li

Acetic anhydride Sodium hydroxide Ammonium sulfide Calcium bisulfide Carbon disulfide Sodium sulfide Sodium sulfite

.5 ppm .2 mg/m3 3 ppm 5 ppm 4 ppm .7 mg/m3 .5 mg/m3

1 ppm .3 mg/m3 4 ppm 8 ppm 6 ppm .8 mg/m3 .5 mg/m3

.75 ppm .25 mg/m3 3.5 ppm 6.5 ppm 5 ppm .75 mg/m3 .5 mg/m3

5 ppm 2 mg/m3 none none 20 ppm none none

.15 .125 0 0 .25 0 0 .525

OSHA PEL*

Ci/Li

Total Em =

n  i=1

9.39.

Ci ----- = .525 Li Morning Exposure (4 hrs)

Substance

< 1 so PEL is not exceeded. > .5 so AL is exceeded. Afternoon Exposure (4 hrs)

Ci 8-hr TWA

Li

Mixture from Ex. 9.38 Formaldehyde

1 ppm

.525 1 ppm

1 ppm

3 ppm .333* *Appendix A.2

Total Em =

n  i=1

.858

Ci ----- = .858 Li

The addition of 1 ppm formaldehyde to the other contaminants pushes up the Em dangerously close to unity, at which point the PEL would be exceeded. An error of only 1 ppm in the expected concentration would push the Em over 1.0. Recommendations to the design engineers should include cautions against the use of formaldehyde unless releases to the atmosphere are closely controlled. Formaldehyde is so hazardous that OSHA has promulgated a separate standard (29 CFR 1910.1048) for its control under the "standards completion project." The tight PEL limits and other contaminants already present in the plant atmosphere warrant serious consideration and "back to the drawing board" process changes. RESEARCH EXERCISES 9.40.

The accident occurred on January 30, 1995. The Arkhangelsk Pulp and Paper Combine of Novodvinsk, Russia emitted up to 16 tons of mercury compounds into the Svernaya Dvina River. The emission of toxic mercury compounds into the river were, and still are, a health threat to the people of the area, and are a threat to the ecological health of the river itself. The contamination of the Svernaya Dvina River at this point was as high as 740 and 640 critical contamination concentrations (cac), on each side of the river. In laymen’s terms, this represents a contamination 20 times greater than the acceptable level for the Svernaya Dvina River at this geographical point. There is danger that the accidental release and the continued release of mercury compounds into the river will result in the death of the river. The Svernaya Dvina River empties into the White Sea and ultimately into the Arctic Ocean. While the much larger body of water represented by the Arctic

Ocean will disperse the concentration rather quickly, the Arctic Ocean, because of the low water temperatures is a much more fragile environment than the waters of more temperate oceans. The Arctic Region is much more sensitive to this type of pollution due to the lack of microscopic organisms that help to neutralize this type of contamination in more temperate regions. Source: Internet http://gurukul.ucc.american.edu/TED.MERCURY.HTM 9.41.

(a) 1910.1052 (b) April 10, 1997 (c) The rate of implementation of the start-up phase depends upon the size of the company and upon the section of the standard, as follows: COMPANY SIZE:



Vol

> 157,282 x 106 ft3

Vol

> 1.57 x 1011 ft3

10-6

Floor Space (in square miles) =

Volume Ceiling Height

= 1.57 x 1011 30 x 52802 = .523 x 1010 = 188 square miles 5.282 x 106

x

[ 1 mile]2 [5280 ft]2

10.18.

(a)

dB 86 84 81 101 75

hrs 1 2 1 1 3 8

Using Table 10.2: n Cn D = 100  ----- = 100 i=1 Tn

1 2 1 1 ----- + ----- + ----- + ---- = 80.47% 13.9 18.4 27.9 1.7

Since 80.47% < 100, PEL is not exceeded. (b) yes (since 80.47% > 50%) (c) yes (d) no (unless the employee has experienced a permanent threshold shift) (e) Afternoon; the 101 dBA contributes more than all other exposures combined. Comparison is as follows: Cut sound in morning: 86 -- 83; 84 -- 81; 81 -- 78 n Cn 1 2 1 D = 100  --- = 100 ---- + ---- + ---- = 70.73% i=1 Tn 21.1 27.9 1.7 Cut sound in afternoon: n Cn 1 2 1 1 D = 100  --- = 100 ---- + ---- + ---- + ---- = 60.11% i=1 Tn 13.9 18.4 27.9 2.6 10.19.

2 Enclose the noise source with a barrier that reduces the noise level by 50%. 1 Position the operator at a distance twice as far from the source of the noise. 3 Rotate personnel so that each worker is exposed to the noise source for only one-half shift. 4

Provide ear protection that cuts the noise level by one half.

Moving the operator away (twice as far) from the noise is best because this change will reduce the noise exposure by a factor of 4 (6 db), whereas the other three alternatives only reduce the noise exposure by a factor of 2 (3 db reduction reduces the absolute sound pressure by a factor of 2). Second in priority is the barrier because it would be considered an engineering control. Third in priority would be rotating personnel, an administrative or "work practice" control. Last in priority would be ear protectors, which would represent personal protective equipment. 10.20.

PEL ---106

=

liberated --------- = exhaust

5 --E

5(106) 5(106) E = -------- = ------- = 5,000 ft3/hr PEL 1000 10.21.

Instead of silica (for blasting), use steel shot. Instead of lead-based paint, use iron oxide pigments. Instead of freon (as a propellant), use propane. Instead of acetylene (for welding), use natural gas, if flame temperature is hot enough.

10.22.

Often operating personnel ignore such alarms as red lights. Even when the alarm is an audible type, operators and/or maintenance personnel may ignore the signals or even deliberately disconnect the wiring to the alarms as an expediency.

10.23.

The purpose is to save energy costs by allowing the transfer of energy between exhaust air and makeup air, that is, from exhaust air to makeup air in the winter months and from makeup air to exhaust air in the summer months. The method is especially effective in cold climates in which much energy is lost via exhaust air. The drawback to the

approach is that it places contaminated air in close proximity to clean makeup air. If there are leaks in the heat exchanger, crosscontamination can result. 10.24.

Exhaust ventilation is being used with insufficient sources of makeup air, probably due to the need to open some windows or doors.

10.25.

X-rays

10.26.

(a) For the design of a ventilation system to protect against safety hazards the appropriate physical characteristic is LEL, "lower explosive limit," which, for ethylene glycol, is 3.2%. The ventilation system must introduce sufficient makeup air to maintain a dilution of the ethylene glycol to less than 3.2%. Although a large room size might accommodate the contamination for a short period, in the long run the ventilation system must keep up with the rate of contamination produced by the process, regardless of the dimensions of the air volume within the plant. Therefore, 2.4 ft3 vent vent

=

=

3.2%

240/3.2

75 ft3/hr

=

(b) To deal with the health hazard the ventilation system must keep the concentration of ethylene glycol at least below the PEL and should be designed to keep it below the action level. The PEL for ethylene glycol is shown in the problem statement to be 50 ppm (ceiling)1, so the AL at 50% of the PEL is 25 ppm. Therefore, 2.4 ft3 vent vent

= =

25 ppm

=

2400000/25

0.000025 =

96000 ft3/hr

(c) Although the room volume of the plant would not affect the design of the general dilution ventilation system to deal with the ethylene glycol hazard, it would determine how many room changes per hour the ventilation system would effect, as follows: Room changes/hr = 10.27.

=

vent per hr/ Room air volume 96000 ft3/hr 12000 ft2 x 16 ft

=

0.5

Plan A: Doubling the distance reduces the absolute sound pressure by a factor of 4. The dB level is thus reduced by half twice (2 x 3 = 6 dB). New dB reading = 96 - 6 = 90 dB. Plan B: Reducing the absolute sound pressure by 75% would new absolute sound pressure of 25% (or one-fourth) of the sound pressure. Therefore Plan B, like Plan A, is also a a factor of 4 or a 6 dB reduction. New dB reading = 96 -

result in a old absolute reduction by 6 = 90 dB

The two plans are equally effective in that each reduces the noise level to 90 dB. If both plans were employed at the same time, each plan would reduce the absolute sound pressure by a factor of 4, resulting in a 16-fold overall reduction. Note that a 16-fold reduction is a halving of the sound pressure four times (24 = 16). Each time absolute sound pressure is halved, sound level is reduced by 3 dB. The sound level is thus reduced by 12 dB (4x3dB = 12dB). New dB reading = 96-12 = 84 dBA. RESEARCH EXERCISES 10.28.

1

A professional recommendation to this employer should first establish whether the general asbestos standard, 29 CFR 1910.1001, applies. Subparagraphs (a)(2) and (a)(3) of this standard exclude construction and ship repairing, shipbuilding, and shipbreaking and if the employer is in these industries, other applicable standards should be consulted. It is assumed in this problem that since none of these special industry categories were mentioned, the general standard applies. In

Note to Instructor: Although the PEL for ethylene glycol is listed in the problem statement for Exercise 10.26 to be 50 ppm, OSHA lists the substance as 2-Methoxyethyl acetate and currently lists its PEL as 25 ppm (TWA) as shown in Appendix A.1 of the text. For purposes of this exercise the solution assumes a ceiling PEL of 50 ppm for this substance, as stated in the problem statement.

subparagraph (f) - Methods of Compliance, the standard for the most part permits either engineering controls or work practice controls to be used to reduce the exposure of employees to acceptable levels. However, the employer’s attention should be directed to several provisions of subparagraph (f)(1) of the standard that specify certain engineering controls and production procedures WHETHER OR NOT ADMINISTRATIVE CONTROLS ARE USED ALSO. Certain asbestos operations REQUIRE local exhaust ventilation, in accordance with 1910.1001(f)(1)(iv) and (v). Specifically, local exhaust ventilation is required for the use of ―hand-operated and power-operated tools which would produce or release fibers of asbestos, such as, but not limited to, saws, scorers, abrasive wheels, and drills.‖ Such local exhaust ventilation is required to be ―designed, constructed, installed, and maintained in accordance with good practices such as those found in the American National Standard Fundamentals Governing the Design and Operation of Local Exhaust Systems, ANSI Z9.2-1979.‖ Another engineering control specified by the standard (1910.1001(f)(1)(vi)) is wet methods ―insofar as practicable‖ whenever asbestos is ―handled, mixed, applied, removed, cut, scored, or otherwise worked‖ in order to prevent the emission of airborne fibers so as to expose employees to levels in excess of the TWA and/or excursion limit specified by the standard. Particular products and operations require one or more ENGINEERING controls as specified by 1910.1001(f)(1)(viii). Specifically, the removing of asbestos ―from bags, cartons, or other containers in which they are shipped‖ requires wetting, enclosure, or ventilation ―so as to prevent effectively the release of airborne fibers.‖ Special engineering control precautions are specified for the use of compressed air for removal of asbestos or materials containing asbestos (1910.1001(f)(1)(ix)). Basically, compressed air is prohibited for this purpose, unless a ventilation system is properly engineered to effectively capture the dust cloud created by the compressed air. Sanding asbestos-containing floor material is prohibited by 1910.1001(f)(1)(x). Another method must be engineered to replace the sanding operations. There are detailed requirements for brake and clutch repair operations; these requirements are specified in Appendix F of the standard. Often the employer uses employee rotation as a work practice control to reduce employee exposure to maximum acceptable time-weighted average exposure levels, but for asbestos operations, employee rotation to achieve compliance is not an option. OSHA standard 1910.1001(f)(2)(iv) specifies that ―the employer shall not use employee rotation as a means of compliance with the TWA and/or excursion limit.‖ These are significant drawbacks to the administrative (work-practice) control strategies, and management should be made aware of these drawbacks. 10.29.

OSHA standard 1910.1001(h)(3)(ii) expressly prohibits ―the removal of asbestos from protective clothing and equipment by blowing or shaking.‖

10.30.

The Lead Industries Association was joined by the Battery Council International along with the Occupational Safety and Health Administration in a voluntary initiative to protect the health of lead workers. This initiative was announced on October 30, 1996 (USDL News Release 96-457): ―Representatives of 33 companies, the vast majority of members in the two associations, have agreed to the program. The companies have 20,000 workers in such industries as battery manufacturing, lead smelting, lead chemicals, fabrication using lead, and solder manufacturing.‖ Two targets were identified, as follows: OSHA Spec

Industries’ Target Initiative

Trigger blood level for relocation of 50 micrograms micrograms workers to an area in which lead exposure is less than the 30 micrograms per cubic meter action level (per 100 grams of whole blood)

40

Blood level target for return to work micrograms (per 100 grams of whole blood)

35

40 micrograms

Both of the above targets were scheduled for a 5-year phase-in with the relocation target to decrease at the rate of 2 micrograms per year and the return-to-work target to decrease at the rate of 1 microgram per year until the 5-year targets are reached.

10.31.

From the OSHA website, the general industry industrial noise standard is found to be OSHA standard 1910.95. This standard contains provisions for exposure to excessive noise plus provisions for monitoring, hearing conservation programs, and personal protective equipment. The NCM database shows that OSHA standard 29CFR1910.95 was cited 2265 times for the fiscal year, and that 1283 of these citations were designated as in the ―serious‖ category. Thus, the percentage of serious violations is 1283/2265 = approximately 57%. The total dollar amount of the penalties proposed for the alleged violations was $1,548,498, for an average penalty per citation of approximately $684.

10.32.

Using the keyword search capability of the NCM database, searching on the term *exhaust hood* returns a tabulation of 122 citations of various standards. Of these 122 citations, 116 were classified as ―serious.‖ Thus, the serious citations represented 116/122 = approximately 95% of the total.

10.33.

Using the OSHA website, the relevant provisions of the OSHA noise standard are listed along with the total number of citations and the number of serious citations for Fiscal Year 2002, as determined from the NCM database:

Serious citations

Total citations Audiometric testing 1910.95(g) 1910.95(h) 1910.95(m)(2) 1910.95(m)(3)(ii) 1910.95(n)(1) Hearing conservation programs 1910.95c 1910.95c1 Totals General ventilation standard 1910.94

502 2 53 1 1

294 0 15 1 0

5 500 1064

3 303 616

201

159

The action level trigger for audiometric testing and hearing conservation programs is 85 decibels. Computing the percentage of citations that are classified as serious, using the total figures alone: Audiometric testing and hearing conservation: 616/1064 = approximately 58 percent General ventilation standard: 159/201

= approximately 79 percent

OSHA cites the noise standard more frequently, but the ventilation standard generates a higher percentage of ―serious‖ citations.

CHAPTER 11

SOLUTIONS TO END-OF-CHAPTER EXERCISES

11.1.

A floating roof is used on many petroleum tanks. The roof rises and falls with the level of the liquid, so that the tank does not require venting. This saves vapor losses and also enhances safety.

11.2.

Yes, if the quantity of explosives does not exceed 50 pounds. A Class II magazine can store any type of explosive. It is restricted by only the amount of explosive stored in it. Fifty pounds or less may be stored in a Class II magazine.

11.3.

An acronym which stands for boiling liquid expanding vapor explosion.

11.4.

The terms ―light‖ and ―heavy‖ refer to ―volatility‖ or how readily a liquid will evaporate. Volatility is closely related to boiling point. ―Light‖ indicates high volatility, so light oils will evaporate more readily than heavy oils.

11.5. Flammable range:

Gasoline 1.4 to 7.6% vapors

Ethyl Alcohol  4 to 20% vapors

A drum of alcohol would have a much greater hazard potential than one containing gasoline because a much wider range of alcohol concentrations in air are burnable. 11.6.

Acetone flammability lower limit  3% vapor concentration. 2 gal. of liq. x 41 ft3 vapor hr. gal. of liq.

=

82 ft3 vapor hr.

Let x = amount of air needed to maintain less than 3% acetone vapor. 82/x < 3/100 x > 82(100)/3 x > 2733 ft3/hr Volume of room = 9 x 12 x 10 = 1080 ft3 2733 ft3/hr = 2.53 times/hr 1080 ft3 11.7.

There will be spray paint residues accumulated throughout the area in large quantities.

11.8.

Automatic sprinkler systems are required for fixed electrostatic paint spraying systems where this protection is available.

11.9.

Dip tank covers are required to be "kept closed when tanks are not in use." Automatic closure is not required.

11.10.

The transportation and storage of LPG in its liquid state in tanks introduce hazards not present for natural gas. The tanks are subject to BLEVE in fires. LPG is heavier than air, causing it to collect in low areas instead of quickly dispersing as does natural gas (methane), which is lighter than air. The liquid state of LPG also can cause skin and flesh burns from the extreme cold when the LPG is released from its tank or connections.

11.11.

Fire extinguishers can be useful for extinguishing small fires before they cause ignition of LPG tanks. Once the LPG ignites, however, fire extinguishers are useless for fighting the fire. Professional firefighters use large quantities of water to fight LPG fires.

11.12.

Using the paint spray area as a drying area can raise the temperature level of the paint residues and also the level of flammable vapors in the air, increasing the fire hazard. The standards prohibit the use of a paint spray area as a drying area unless the arrangement does not "cause a material increase in the surface temperature of the spray booth, room, or enclosure.

11.13.

The key to the solution of this problem is to recognize that the objective with general exhaust ventilation is to maintain adequate ventilation levels to introduce sufficient makeup air to keep the contaminant release within limits. Room size (volume) makes a difference at first but does not affect the long-run solution to maintaining contaminant levels below limits.

(a) For dealing with safety hazards the objective is to keep carbon disulfide levels below the lower flammable limit, which was stated in the problem statement to be 1.3% Let x = the required ventilation level: 3 ft3/hr x x

=

0.013

=

3/0.013

=

231 ft3/hr

(b) For dealing with health hazards the objective is to keep carbon disulfide levels below the 8-hr TWA PEL: 20 ppm Let y = the required ventilation level: 3 ft3/hr y y

=

0.000020

=

3/0.000020

=

150,000 ft3/hr

(c) The flashpoint of carbon disulfide is shown in the problem statement to be -22 oF, and the boiling point is 46.5oC. The flashpoint identifies the liquid as Class I. The boiling point is converted to Fahrenheit as follows: B.P. (Fahrenheit) = 46.5

o

C x 9/5 + 32

o

= 115.7

o

F

o

Since the boiling point is greater than 100 F, carbon disulfide is classified as a Class IA liquid. (See Figure 11.1) 11.14.

No difference. liquids.‖

Another name for Class I liquids is ―flammable

11.15.

The danger of the ―empty‖ gasoline drum is that the vapors have thinned to the point that they may be within the burnable range, i.e., less than the UEL but still greater than the LEL. In a full tank of gasoline the vapors are virtually certain to be in greater concentration than the UEL. For carbon disulfide, however, the range of burnable concentrations is much greater. The LEL for carbon disulfide is 1.3% and the UEL is 50%, a range of 48.7%. For gasoline the range is much narrower at 6.2% (7.6% UEL - 1.4% LEL = 6.2%).

11.16.

The hazard is that the vapor density of gasoline is greater than that of air. The heavier gasoline vapors will tend to displace the air and collect in the basements of service stations, creating dangerous concentrations.

11.17.

Kerosene is combustible and therefore has a higher flashpoint than gasoline. At the same temperatures, gasoline is much more dangerous and ignitable. However, if the kerosene is heated, it can become even more dangerous and ignitable than gasoline.

11.18.

Ethyl mercaptan is a stenching agent added to propane to facilitate leak awareness and detection.

11.19.

It’s OK to refuel forklift trucks with the engine still running, if the forklift is LPG-powered. This is despite the fact that federal standards prohibit refueling of forklift trucks while the engine is still running if the fueling operation involves venting to the atmosphere. LPG refueling does not require venting to the atmosphere.

RESEARCH EXERCISES 11.20.

Pyrogen. Ref Internet website: http://www.pyrogen.com/ FE-241 is a liquefied compressed gas similar to Halon. It is classified as "clean agent", meaning it leaves no residue as a result of the agent itself. Its chemical name is Chlorotetrafluoroethane. Like Halon, it chemically inteferes with the combustion process for fire extinguishment. Ref Internet website: http://www.fireboy-xintex.com

Halotron™ I: Halotron, Inc. manufactures environmentally acceptable clean (leaving no residue) fire extinguishing agents, including Halotron™ I, which are replacements for the halons. In developed countries, production of Halons 1211 and 1301 was stopped on January 1, 1994. Ref Internet website: http:halotron-inc.com Microblaze Out:

Microbial firefighting agent.

Ref: Internet website:

http://www.micro-blaze.com 11.21.

The Shepardsville, Kentucky train derailment involved an 89-car freight train carrying hazardous materials and explosives. The trained derailed and hurtled into the Salt River in this small town approximately 20 miles south of Louisville. The town of more than 1,000 population was evacuated to a Red Cross shelter at a nearby county fairgrounds. Several train cars were set on fire. One car that was not burning, but was close to another burning car, contained Methylene Diphenyl Diisocyanate. This chemical is not only flammable; it is extremely poisonous and is chemically similar to the Diisocyanate that was released in Bhopal, India with disastrous results. Fire and disaster officials were fearful that the firefighters would be endangered and declined to send them into the immediate area of the fire. Another concern was BLEVE. A BLEVE of a material that is both poisonous and flammable could be a disastrous event, but there is the possibility that the burning that takes place in a BLEVE could serve to consume the material in question or neutralize its toxic effects. The problem is that some of the material might not be completely consumed by the BLEVE, and the potentially deadly, partially destroyed, byproducts of the combustion would be released and even further dispersed into the air. Reference source: The above facts were gathered from the Internet in 1998 at ―EMERGENCYNET NEWS‖ 11-19-91 2300 CST. At the time of publication of this Solutions Manual the Internet URL containing the particulars on this accident was no longer available on the Internet. The difficulty for students who are assigned this research exercise is substantially increased due to the unavailability of this URL on the Internet. Instructors should take this into consideration in making assignments to students.

11.22.

The tank arrangement is poorly designed. Tank #1 is splash loaded, but a more serious design problem actually caused this accident. The tank interconnection at the bottom is quickly immersed in liquid as soon as filling begins. This forces tank #2 to fill before tank #1. Because there is no separate vent for tank #1, a bubble of air in tank #1 prevents its filling, and when tank #2 is full, it starts to overflow from the vent pipe when only 250 gallons have been delivered. The large, unexpected spill through the vent pipe was the principal cause of the explosion. The flashpoint of tetrahydrofuran is 6 degrees Fahrenheit. (ref. Handbook of Organic Industrial Solvents, Alliance of American Insurers, 1981)

11.23.

The six frequently violated conditions are described by several provisions of the OSHA standard. From the OSHA website the various provisions of OSHA standard 29CFR1910.107 – Spray finishing relevant to the six areas are listed below, with citation counts shown for each. The source of the citation counts is the NCM database. Electrical wiring for hazardous locations: 1910.107(c)(4) – 12 citations 1910.107(c)(5) – 55 citations 1910.107(c)(6) – 165 citations

for a total of 232 citations

Exhaust air filter deficiencies: 1910.107(b)(5)(i) – 268 citations 1910.107(b)(5)(ii) – 9 citations 1910.107(b)(5)(iv) – 119 citations 1910.107(b)(5)(vi) – 1 citations Cleaning and residue disposal:

for a total of 397 citations

also,

1910.107(g)(2) – 199 citations 1910.107(g)(3) – 64 citations 1910.107(b)(9) (accessibility for cleaning) – 148 citations for a total of 411 citations

Quantities of material in storage: 1910.107(e)(2) – 146 citations

for a total of 146 citations

Grounding of containers: 1910.107(e)(9) – 94 citations also, 1910.107(i)(6) (general grounding, incl containers) – 4 citations for a total of 98 citations NO SMOKING signs: 1910.107(g)(7) – 1910.107(m)(2) –

93 citations 3 citations

for a total of 96 citations

The total number of citations of alleged violations of the relevant provisions: 232 + 397 + 411 + 146 + 98 + 96 = 1380 citations The total number of citations of alleged violations for the entire spray finishing standard (OSHA standard 1910.107) = 2058 Therefore, the citations for the ―top six‖ frequently cited conditions represents 1380/2058 = approximately 2/3 of the total citations for the spray finishing standard. Source: NCM database 11.24.

OSHA has recently changed the organization of standards pertaining to dip tanks. Formerly the principal standard was OSHA standard 29CFR1910.108 – Dip Tanks containing flammable and combustible liquids. As of this writing, this standard was still listed on the OSHA website in the Table of Contents for the OSHA General Industry 1910 standards. However, the text of this standard has been removed and placed in other standards, leaving 1910.108 with only the word ―reserved‖ in the text content. Currently, there are four principal standards for dip tanks: 1910.123 – Dipping and coating operations – Coverage and definitions 1910.124 – General requirements for dipping and coating operations 1910.125 – Additional requirements for dipping and coating operations that use flammable and combustible liquids. 1910.126 – Additional requirements for special dipping and coating operations OSHA citation activity for dip tanks in general is not very significant in recent years, as can be seen from the NCM database. Also, the focus has shifted somewhat from the former emphasis on such items as covers and automatic extinguishing systems. The three most frequently cited items in all of the ―dipping and coating operations‖ standards are the following: 1910.124(g)(2) – Emergency shower and eyewash facilities 1910.124(h)(4) – Exposure to chromic acid, exposed body parts, especially nostrils (Note: see discussion of ―chrome holes‖ in Chapter 12 of the text in the discussion of personal protective equipment around open-surface tanks) 125(e)(5) – No smoking in vapor area near dip tanks Source: NCM database

11.25.

The OSHA website shows that the principal standard for LPG is OSHA standard 29CFR1910.110 – Storage and handling of liquefied petroleum gases. The NCM database shows that for the fiscal year 1910.110 was cited 558 times, of which 292 citations were listed as ―serious.‖ Of these 558 citations, the most frequently cited provisions were: 1910.110(f)(2)(i) 128 citations (location of LPG containers in storage) 1910.110(d)(10) 69 citations (precautions to prevent damage from vehicular traffic) 1910.110(f)(2)(ii) 63 citations (inside storage of LPG near exits) 1910.110(e)(4)(iii) 58 citations

(secure mounting of tanks, but no field welding on the tanks themselves; field welding only on the original lugs) The above four provisions accounted for more than half of all citations issued for LPG alleged violations for the fiscal year. Source: NCM database

CHAPTER 12 SOLUTIONS TO END-OF-CHAPTER EXERCISES 12.1.

The employer of the employees who will be potentially exposed.

12.2.

Selection of appropriate PPE equipment, fit testing, and PPE training for affected employees. The training must be documented with a certificate that identifies the names of employees trained, the dates, and the subject for which the employee was certified.

12.3.

Retraining is needed if either the workplace is changed or if the PPE is changed.

12.4.

Simply attaching a lifeline to a worker’s belt may not be adequate. The belt may not withstand the shock load of an accidental fall. Further, the practice might engender a false sense of security on the part of the worker, who might think that he/she is protected, but in truth the protection might not be adequate for the hazard.

12.5.

The non-mandatory appendices to the OSHA standards can provide some guidance. NIOSH publishes some data to assist employers in this decision and also publishes the list of NIOSH certified equipment. The preambles to the OSHA standards can also be helpful in this regard. Table 12.1 of the text provides some guidance for eye and face protection. Expert consultants can also be beneficial, but the hazard usually dictates the choice of equipment or at least greatly narrows the choice.

12.6.

Whenever it is determined that the personal protective equipment is needed.

12.7.

The employee needs to learn that PPE is limited to a finite useful life even under proper care and maintenance.

12.8.

By documentation with a certificate showing names, dates, and subject for which the employee is certified. Employees should be knowledgeable of the subject for which they are trained. If the workplace or the equipment changes, the employee should be retrained.

12.9.

Ordinary cotton balls, without impregnation with a wax, are virtually worthless for noise attenuation.

12.10.

Helmets. Helmets can also be designed to serve the function of a hardhat.

12.11.

The organic substances present in expandable foam do not have adequate warning properties, so the user will not know when the canister is saturated.

12.12.

A chemical oxygen-generating unit employs a superoxide of potassium in which oxygen is liberated by contact with water. Used in "closed circuit" breathing apparatus, the moisture is supplied by the user's breath. A water flooding of the potassium superoxide is almost sure to cause an explosion.

12.13.

"Closed-circuit" respirators would be best for circumstances when use of a self-contained breathing apparatus is required for extended periods of time because "closed-circuit" respirators can be smaller and lighter per minute of maximum permissible use than "open-circuit" respirators.

12.14.

Pressure demand. If the facepiece becomes leaky, the "demand flow" type would allow the contaminant to enter the mask.

12.15.

Training of employees to beware of and test for hazardous atmospheres in tanks, and training in emergency situations (including first aid). Management should have procedures requiring testing of possible hazardous areas, and the wearing of personal protective equipment for employees working in areas where hazards do exist.

12.16.

Street safety lenses and industrial safety lenses. Industrial safety lenses are more durable.

12.17.

Requiring workers to wear protective equipment in areas where the protective equipment is not needed may result in workers not respecting the rules, leading to injuries to workers.

12.18.

Operators of grinding machines, drill presses, and lathes. other machining operations that produce chips or sparks.

Also any

12.19.

Federal regulations require a respirator to be labeled as "organic vapor respirator" because it has passed a certain prescribed test, even though the respirator may be useless for certain organic vapors. There are so many organic vapors that it would be impossible to label a respirator for all organic vapors against which it is effective. Manufacturers' recommendations (tables) should be consulted.

12.20.

Hardhats are personal protective equipment and do not "prevent accidents;" they only minimize the adverse effects of accidents. Engineering controls to remove the hazard is a preferable approach, but since elimination of all risk is impractical, there is a need for personal protective equipment such as hardhats.

12.21.

The need for personal protective equipment implies that the hazard has not been eliminated or controlled.

12.22.

The employee may have inadequate equipment, yet the employer still is responsible to provide adequate protection to its workers. Also, employee-owned inadequate equipment can create a dangerous, false sense of security.

12.23.

The undersized manholes prevent entry of personnel wearing selfcontained breathing apparatus.

12.24.

In an actual fall the shock load applied to the fall protection system would be much greater than the static load of the wearer’s body weight.

12.25.

Use wire baskets for handling the parts in the solvent. soap and water for the trichloroethylene in some cases. process to eliminate the need for washing parts.

12.26.

In the heat of the emergency there is a strong tendency to try to save the first victim. There is a tendency for the rescuer to think that what happened to the first victim will not happen to him, because he is already aware of the danger and thinks that he can be especially alert to his own symptoms and get out quickly if he gets into trouble.

12.27.

1. 2. 3. 4. 5. 6.

12.28.

Engulfment is entrapment in a fluid-like granular solid, such as grain or sand, which causes the victim to sink deeper with every movement. Death comes from suffocation due to the breathing passages becoming blocked or due to the source of air being cut off by the engulfing material. In addition, death can come due the crushing weight of the material closing in around the victim.

12.29.

This hazard is called ―entrapment.‖ Most mechanical entrapments occur in a space that is ever-tightening and restricting as it descends. As the victim moves to attempt to free him/herself he slides deeper into the more restricted space, further impairing his freedom to move and free himself. Eventually, the restriction firmly traps the victim, and no escape is possible without rescue. Death can come relatively quickly from suffocation in the small dimensions of the breathing space near the victim. If adequate oxygen supply is available to the victim, an even worse death can come agonizingly slowly.

12.30.

Inerting is intended to reduce oxygen content to reduce the hazards of fire, especially around welding operations. However, oxygen deficiency becomes a suffocation hazard to any workers in the oxygen deficient space.

12.31.

Oxygen enrichment causes fires to ignite easily and burn furiously. situations that most workers would expect to be harmless, oxygenenriched atmospheres can cause surprising ignitions.

12.32.

IDLH means "immediately dangerous to life or health" and usually refers only to the toxicity of the particular air contaminant present. However, in a confined space, an air contaminant that might only be a mild depressant under normal circumstances could become lethal by paralyzing the victim and preventing his or her escape from the danger zone.

Substitute Change the

Oxygen deficiency (primary hazard) Mechanical entrapment Engulfment (from granular solid material) Oxygen-rich atmosphere (fire hazard, especially to welders) Highly toxic atmospheres Escape impairment from mildly toxic, but temporarily paralyzing atmospheres.

In

12.33.

Close all valves that govern piping that might lead dangerous liquids, gases, or even solids into the confined space. Use a double-block-andbleed procedure that closes two valves in series in a pipe leading into the space, and in addition opens a small bleed valve in the pipe in the space between the two major valves. The bleed valve allows the escape of any fluids that might accumulate due to high pressure differential on the primary major valve. The secondary major valve thus has little or no pressure differential across it and can achieve a positive closure. Another procedure for positive isolation is ―blanking‖ or ―blinding,‖ in which a solid plate is installed in the line completely covering the cross-sectional area of the pipe and absolutely blocking flow. Another procedure is to physically sever the line and detach and separate the two remaining lengths of pipe.

12.34.

Oxygen deficient atmosphere. A gas mask is an air purifying device and thus removes air contaminants but does not add the crucial ingredient -- oxygen.

12.35.

Hydrogen fluoride and cadmium vapors are insidious in that their immediate effects are transitory. Thus, even if these transient effects are severe, they may pass without medical attention. However, they are often followed by delayed reactions such as sudden, possibly fatal collapse 12 to 72 hours after exposure.

12.36.

A superficial respirator program might lull employees into a false sense of security. Later, if a real respiratory problem develops, the partial program will be inadequate to deal with the problem, and workers will not be protected. Bad habits such as negligent maintenance, inadequate fit testing, or improper equipment usage could be present without consequence, if the program is not really needed to begin with. A feeling of complacency toward the use of respirators can be engendered by the use of such equipment when it is not really needed.

12.37.

―Double-block-and-bleed‖ refers to a procedure for isolation of a confined space which closes two valves in series in a pipe leading into the space, and in addition opens a small bleed valve in the pipe in the space between the two major valves. The bleed valve allows the escape of any fluids that might accumulate due to high pressure differential on the primary major valve. The secondary major valve thus has little or no pressure differential across it and can achieve a positive closure.

RESEARCH EXERCISES 12.38.

At least one accident has been reported in the area of working in the confined space of a service pit for a display waterfall (fountain) in a shopping mall. An employee lost consciousness when he descended seven feet to the bottom of a service pit to adjust valves for the fountain. A companion worker entered the pit to rescue the first worker and also lost consciousness. A security guard and a passerby tried to assist but became dizzy. The fire department was summoned to the scene and both employees were revived and were treated and released. OSHA investigated four such service pits in this shopping mall and found three of the four had oxygen concentrations of less than the minimum acceptable 19.5 percent. In addition, carbon dioxide readings were more than double the OSHA PEL. Similar problems have been studied by NIOSH. References: This story was first found on the Internet at the UniHoist Newsletter. Uni-Hoist is a manufacturer of confined space entry equipment. The URL used to find this data on the Internet was: http://www.cdnsafety.com/unihoist.html This URL may no longer be available. Other articles describing confined space hazards may be found at http://www.cdnsafety.com/articles.htm Data on this accident may also be available on the OSHA website. OSHA changes the organization of the website from time to time. At the time of this printing in 2003, a description of this accident was found in a Hazard Information Bulletin, dated June 13, 1996, by doing a search on the term ―waterfall‖ in the OSHA website search facility entitled ―Find it! In DOL‖

12.39.

―Air-off‖ conditions represent a real hazard, especially when workers are in a dangerous atmosphere. When sudden air-off occurs, workers are afraid to remove the suit top or helmet in a contaminated atmosphere environment, so they try to quickly escape to a safe area before removing the headgear. Unfortunately, oxygen-deficiency becomes a more serious hazard than the contaminated atmosphere, in many cases. Tests

have shown that oxygen levels can be depleted inside the suit to a dangerous 16 percent in only 40 seconds! The situation can deteriorate into a life-threatening situation very quickly. Besides escape situations, simple donning and doffing of air-supplied suits during training exercises without turning on the supplied air can result in dangerous oxygen-deficiency. Especially because of the escape hazard, the Department of Energy (DoE) has issued directives that workers should be trained to give precedence to preventing oxygen-deficient atmosphere inside the suit at the expense of sacrificing contamination control. Original reference for this information: ―Potential Oxygen Deficiency While Wearing Air-Supplied Suits,‖ DOE/EH-0414, Issue No. 96-1, April, 1996. 12.40.

The problem is at least as prevalent in grain bins as in sand bins. Many fatalities have been reported. Suffocation in flowing grain is the most common cause of death associated with grain storage structures in the United States (Ref 2,3, below). During 1985-1989, suffocation accounted for 49 grain- and silage-handling-associated fatalities (Ref 4, below). Research has shown that victim can become trapped as quickly as five seconds after the unloading auger starts at the bottom of the bin. Complete immersion can occur in approximately 22 seconds (Ref 1, below). Another source (Ref 2,3 below) states that ―a person can become completely submerged in the flowing grain in 8 seconds.‖ A 1-foot deep pile of corn, lying on a typical man, 6 feet tall and lying down, weighs approximately 300 pounds. References: 1. Loewer, Otto J., and David H. Loewer, ―Suffocation Hazards in Grain Bins,‖ Kentucky Cooperative Extension Service Bulletin. Lexington, Kentucky: University of Kentucky, 1975; publication no. AEN-39. 2. Baker DE. Safe storage and handling of grain. Columbia, Missouri: University of Missouri, Columbia Extension Service, October 1983. 3. Aherin RA, Schultz L. Safe storage and handling of grain. In: Minnesota Extension Service Bulletin. St. Paul, Minnesota: Minnesota Extension Service, 1981; publication no. AG-FO 568. 4. Snyder KA, Bobick TG, Hanz JL, Myers JR. Grain-handling fatalities in production agriculture, 1985-1989. Presented at the 1992 International Winter Meeting, Division of Safety Research, National Institute for Occupational Safety and Health. St. Joseph, Michigan: American Society of Agricultural Engineers, 1992; paper no. 92-5509. 5. ―Suffocations in Grain Bins -- Minnesota, 1992-1995,‖ Morbidity and Mortality Weekly Report October 4, 1996/Vol. 45/No. 39 U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention

12.41.

A good comparison of various hazards for methane can be found in the Preamble to the ―Permit-Required Confined Space Entry‖ standard, found in the Federal Register and the OSHA website. The following is quoted from that preamble: ―Some chemical substances present multiple atmospheric hazards, depending on their concentration. Methane, for example, is an odorless substance that is nontoxic and is harmless at some concentrations. Methane, however, can displace all or part of the atmosphere in a confined space(1); and the hazards presented by such displacement can vary greatly, depending on the degree of displacement. With only 10 percent displacement, methane produces an atmosphere which, while adequate for respiration, can explode violently. By contrast, with 90 percent displacement, methane will not burn or explode, but it will asphyxiate an unprotected worker within about 5 minutes. __________ Footnote(1) Methane is lighter than air when both are at the same temperature (the normal case), and the configuration of some confined spaces can trap accumulating methane at "ceiling"level. On the other hand, in the unlikely event that liquified methane is released into the atmosphere of a confined space, the methane released would be heavier than air and would displace the air from the "ground" level up.

12.42.

The best source for finding the requested background information on any promulgated standard is in the preamble to the standard published in the Federal Register by OSHA at the time of promulgation. The following is quoted from the Preamble to the ―Permit-Required Confined Space Entry‖ standard, found in the Federal Register and the OSHA website:

a. NIOSH definition of ―confined space‖: ―a space which by design has limited openings for entry and exit, unfavorable natural ventilation which could contain or produce dangerous air contaminants, and which is not intended for continuous employee occupancy.‖ b. Three classes of confined spaces, as prescribed by NIOSH: 1. Class A – immediately dangerous to life or health 2. Class B – dangerous 3. Class C – confined spaces in which the potential hazard would not require any special modification of the work procedure. c. Three employer ―problems‖ associated with confined spaces were published in an ―Alert‖ titled ―Request for Assistance in Preventing Occupational Fatalities in Confined Spaces‖ (NIOSH, January, 1986), as follows: 1. recognizing confined spaces 2. testing, evaluating, and monitoring confined space 3. developing and implementing rescue procedures. d. In January 1986, NIOSH published an "Alert" titled "Request for Assistance in Preventing Occupational Fatalities in Confined Spaces" (Ex. 13-16). The Alert described the circumstances under which 16 workers died (14 of them due to atmospheric hazards) in confined space incidents. NIOSH focused on problems employers have in three areas: (1) recognizing confined spaces; (2) testing, evaluating, and monitoring confined space atmospheres; and (3) developing and implementing rescue procedures. It was noted, for example, that "[m]ore than 60% of confined space fatalities occur among would-be rescuers." The Alert recommended that employers protect employees who enter confined spaces by implementing measures similar to those presented in the 1979 Criteria Document. e. According to the January 1986, NIOSH-published "Alert" titled "Request for Assistance in Preventing Occupational Fatalities in Confined Spaces": "[more than 60% of confined space fatalities occur among would-be rescuers." (found in the Preamble to the ―PermitRequired Confined Space Entry‖ standard, published in the Federal Register and the OSHA website) 12.43.

From the OSHA website it can be determined that the general standard for confined space entry is OSHA standard 29CFR1910.146 – ―PermitRequired Confined Space Entry.‖ Section a. (Scope and application) specifically excludes agriculture, construction, and shipyard employment from coverage under the standard. The preamble to the standard explains that these areas are covered under other standards. The preamble also contains discussion and arguments over the scope of the standard. The telecommunications industry argued that it should be excluded, but an exclusion for the telecommunications industry does not appear in the Section a. Scope and application paragraph of the standard.

12.44.

Specific information on the telecommunications industry was included in the Preamble to the ―Permit-Required Confined Space Entry‖ standard published in the Federal Register and the OSHA website, as follows: Estimate of the number of telecommunications manholes in the United States: 1,000,000 It has been argued that telecommunications manholes should be excluded from coverage as ―confined spaces‖ in the general OSHA standard. Quoting testimony from the telecommunications industry in the preamble: ―there are huge differences in confined spaces in chemical and manufacturing plants in telecommunication manholes. First and foremost, the inherent hazard of telecommunications manholes is significantly less. Telecommunication manholes are not designed to contain any kind of chemical or hazardous substance. They do not contain a residual hazardous atmosphere. Telecommunication manholes exist to provide access to underground telephone cables and conduits during splicing, testing, maintenance and air pressurization operations. In most cases, the atmosphere in telecommunication manholes is the same as that outside the manhole. Secondly, telecommunications manholes are located in and around public roads and rights-of-way all over the United States………. While there is no question as to the need for special procedures to protect employees who enter telecommunications manholes, to be effective in saving lives, these procedures must reflect the difficulties inherent in having such a large, widely-scattered workforce. Telecommunications manhole entries are routine, performed on a daily basis and, based on data in OSHA's current record, done safely. The third major difference is that entry into telecommunications

manholes is already regulated by OSHA.‖ According to the preamble: ―GTE has about 8,700 employees who will enter telecommunications manholes approximately 320,000 times a year.‖ (This is interpreted to be a total figure. Dividing 320,000 by 8,700 yields an average per employee of approximately 36 or 37 times per year. According to the preamble: ―Entry into telecommunications manholes and unvented cable vaults is currently regulated by Section 1910.268(o)(2).‖ 12.45.

The NCM database can be used to perform a keyword search on the term *respiratory protection*. Such a search returns a long list of citations, the vast majority of which are in the general respiratory protection standard, OSHA standard 29CFR1910.134. Some other respiratory provisions of specialized standards are also included in the list, especially in the standards included in the ―standards completion project‖ (refer to Table 9.1 in the text, page 187). The total number of citations listed in the NCM database for the term ―respiratory protection‖ is 9101. The corresponding search using the ―serious violations‖ search capability reveals a total of 4206 citations, or 4206/9101 = 46 % of the total. A search of the database can be focused on general personal protective equipment by using the keyword search term *personal protective equipment*. Such a search, using the NCM database, shows a total of 4927 citations. Doing a similar search by ―serious violations‖ a total of 3285 is shown, or 3285/4927 = 67 % of the total. So, comparing the terms ―respiratory protection‖ and ―personal protective equipment‖ as they appear in standards cited by OSHA during the fiscal year reported in the NCM database, standards containing the term ―respiratory protection‖ have resulted more citations, but a greater percentage of the standards containing the term ―personal protective equipment‖ have been in the ―serious violation‖ category. Both terms are involved in frequent citation activity, and a large percentage of citations for both of these terms are designated as ―serious.‖

12.46.

Using the NCM database keyword searching capability, a search for the term *medical services and first aid* results in a printout of several standards containing this word group. The most heavily cited standard is OSHA standard 29CFR1910.151(c). The OSHA website reveals that this standard is the general requirement for medical services and first aid. If all provisions containing the word group ―medical services and first aid‖ are included, the NCM database shows a total of 1887 citations for the fiscal year. Another search for the same word group, using the ―serious violations‖ option of the NCM database keyword search capability, a total of 1283 citations is shown. Thus the percentage of total alleged violations that are in the ―serious‖ category is 1283/1887 = approximately 68 %. Apparently, OSHA takes the subject of ―medical services and first aid‖ quite seriously.

CHAPTER 13

SOLUTIONS TO END-OF-CHAPTER EXERCISES

13.1.

This question is intended to generate class discussion. The argument for fire extinguishers is that they stop fires immediately before the fires become dangerous. The argument against fire extinguishers is that they may endanger workers more than would a policy of immediate escape. The principal purpose of fire extinguishers is to protect property.

13.2.

(1) fire prevention (2) fire suppression (3) personal protection (escape)

13.3.

Fire extinguishers are primarily for property protection, and employees may be safer by simply evacuating the area in case of a fire.

13.4.

Workplace violence

13.5.

One of the world's worst

13.6.

Residential

13.7.

Reported statistics are usually a year or two after-the-fact. The text reports ―approximately 3 percent.‖ The National Safety Council publication Injury Facts, 2002 edition, reporting for the nine-year period from 1992-2000 (using Bureau of Labor Statistics data) reports 1760 fatalities from the general category ―fire and explosions.‖ Total number of fatalities reported for the period is 55,919. By these statistics, the percentage can be calculated to be 1760/55919 = 3.15 %.

13.8.

(a) (b) (c) (d) (e)

13.9.

Overheated bearings or hot machinery and processes are a principal cause of industrial fires. Preventive maintenance could reduce the chance of fire caused by these circumstances. Also important would be clogged ventilation filters which need changing or dirty ventilation ducts. Preventive maintenance is the solution for these problems.

13.10.

Audible alarms are obviously ineffective for deaf employees. But even worse is the complacency which is sometimes created by a wide variety of audible alarms or signals for conditions of various degrees of urgency.

13.11.

No

13.12.

The employee may not want to alarm other workers, thinking that the fire is being taken care of.

13.13.

No. However, OSHA prescribes requirements for the organization, training, and personal protective equipment of fire brigades whenever they are established by an employer.

13.14.

Quarterly, for firefighters of interior fires; annually, for other fire brigade members

13.15.

Heart disease, epilepsy, emphysema, ruptured eardrums, wearing a beard

13.16.

Referring to Table 13.1:

Class A B C D

anticipation of fire hazards assignment of responsibility for controlling hazards documentation of decision preventive maintenance housekeeping procedures

Description Paper, wood, cloth, etc Flamm/combust liquids, gases, etc. Energized electrical equipment Combustible metals

Example extinguisher media Foam, loaded stream, dry chemical, water

Bromotriflouromethane, carbon dioxide, dry chemical, foam, loaded stream Bromotriflouromethane, carbon dioxide, dry chemical Special powders, sand

13.17.

Powerful water spray systems

13.18.

By referring to Table 13.1, it can be seen that only one extinguisher medium meets specifications for fire Classes A, B, and C, all three. That medium is dry chemical.

13.19.

Dry chemical extinguishers may be approved for more than one class of fire; however, the chemical may foul or ruin expensive equipment (computers, for example); and they may be more expensive than foam and water extinguishers. Also, dry chemical powders may be subject to caking, which would make them ineffective when deployed.

13.20.

1. monthly, by visual inspection 2. annual maintenance and a hydrostatic test, depending on type of extinguisher

13.21.

No, the employer may select any convenient mounting scheme, provided that the extinguishers are readily accessible without subjecting employees to possible injury.

13.22.

Training is required upon initial entry to a job and at least annually thereafter.

13.23.

(1) (2) (3) (4)

13.24.

Direct city water supplies usually cannot meet the flow requirement of 100 gpm for 30 minutes (insufficient dynamic pressure).

13.25.

No, not in general; however, certain electrostatic spray painting areas are required to have automatic extinguishing systems.

13.26.

The paper bag will prevent the sprinkler head from becoming fouled by paint spray residues. The bag will be burned away or washed away by the water spray when the sprinkler is activated.

13.27.

There must be an 18 inch minimum vertical clearance between the sprinkler head and the stacked material.

13.28.

By weight

13.29.

Carbon dioxide, Halon 1211, Halon 1301

13.30.

Ruptured eardrums would prevent effective use of respiratory protective equipment, i.e. the worker would inhale through the ears.

13.31.

Audible siren, public address, direct voice

13.32.

Preventive maintenance and housekeeping

13.33.

Imperial Foods poultry processing plant in Hamlet, North Carolina; 25 fatalities; the fire did its damage in only 35 minutes; a principal factor in the tragedy was locked exits.

13.34.

Triangle Shirtwaist Company, New York, 1911; 145 fatalities.

13.35.

No; OSHA standards require the standpipe system to maintain a flow of 100 gallons per minute for 30 minutes as a minimum. This amounts to 30 x 100 = 3000 gallons total delivered in the minimum 30 minute period required. The system as described does have 3000 gallons capacity. However, if the pressure that causes the flow is "gravity head," as is stated in the problem, then as the flow nears exhaustion, there would no longer be sufficient head to drive the flow. This system design is inadequate to meet flow standards.

13.36.

Static pressure is measured while the system is standing at rest with no flow. Dynamic pressure is the pressure maintained on the liquid while it is flowing. Two different standpipe and hose systems might have identical static pressures when they are not in use, but once flow starts, one system might be designed to maintain its pressure while flowing, but the other might lose pressure immediately upon commencement of the flow.

Shut-off-type nozzles Lining for hose Dynamic pressure minimums at the nozzle Hydrostatic testing upon installation

13.37.

Not anymore; tags were once required and OSHA heavily cited this standard throughout industry; now alternative procedures are permitted such as maintaining the inspection status in a filing system. However, many companies still use the tags so that the record of the inspection status is readily available right on the fire extinguisher, instead of tucked away in a file that might be difficult to find during an inspection.

13.38.

Up to one year after the last entry or the life of the shell, whichever is less.

13.39.

The hydrostatic test is an integrity check of the fire extinguisher shell itself to assure that it is still capable of containing the pressures to which it will be subjected in a fully charged state. Fire extinguisher shells do not last forever; they can corrode or be damaged mechanically. The hydrostatic test reveals any inadequacy in the condition (strength) of the shell.

13.40.

Hydrostatic tests are controlled by technical specifications and must be done by a trained person using suitable equipment and facilities. Few companies would have such specialized equipment on site.

13.41.

1. 2.

13.42.

One of the positive-pressure types: either pressure demand or continuous flow. If the third type, demand flow, is essential in order to permit longer duration exposure for a given charge, then quantitative fit testing is required for each firefighter.

13.43.

A consultant should advise that fire extinguishers are not appropriate for extinguishing LPG fires. Technically speaking, an LPG fire is Class B, but Class B fire extinguishers are not appropriate for this type of flammable liquid or gas. What is needed for LPG is a professional firefighter using powerful, high-pressure water-spray systems. Ordinary Class A type extinguishers may be of value in extinguishing ordinary wood or paper fires in areas where they could threaten LPG storage and thus result in a much more dangerous LPG fire. (See also Chapter 11 for additional discussion of this subject.)

Corrosion Mechanical damage

RESEARCH EXERCISES 13.44.

Answers to this exercise will vary somewhat from year to year. The data shown below were taken from the 2002 edition of the National Safety Council’s Injury Facts. The data reflect overall totals and averages for industries of all types nationwide for the nine year period 1992-2000: Number of Fatality cause fatalities Percent Total, all causes Falls Electrocutions Oxygen deficiency Exposure to harmful substance Transportation accidents Assault, violent act Fires, explosions (not included in the above categories)

55919 5880 not listed not listed 5123 23372 10287 1760 9497

100.0% 10.5 N/A N/A 9.2 41.8 18.4 3.1 17%

Although the reported statistical classifications and numbers of fatalities vary somewhat from year to year, it is clear that motor vehicle accidents is the consistent leader, and workplace violence is second among causes of workplace fatalities. By comparison, fire is a much more benign cause of workplace fatalities, at about 3 percent of the total.

STANDARDS RESEARCH QUESTIONS

13.45.

The appropriate OSHA General Industry standard for Portable Fire Extinguishers is 29CFR1910.157, as can be determined from the OSHA web site. According to the Scope and Application section of this standard (1910.157(a)), OSHA specifies requirements for portable fire extinguishers to ―apply to the placement, use, maintenance, and testing of portable fire extinguishers provided for the use of employees.‖ Note that the foregoing statement does not state that all general industry facilities are required to have portable fire extinguishers. The statement specifies what rules apply only when such extinguishers are ―provided for the use of employees.‖ Alternative strategies for dealing with fire hazards are recognized by OSHA. See OSHA standard 29CFR 1910.156 for rules pertaining to the strategy of maintaining fire brigades for fighting fires ―whenever they are established by an employer.‖ For non-portable fire extinguishers (fixed extinguishing systems), OSHA has specific requirements to protect employees from the hazards of using such systems. The requirement for using such systems may appear in standards specific to a particular fire hazard.

13.46.

OSHA’s principal concern with fire brigades is the protection of the workers who are designated to serve in such capacity. Fire suppression has a principal objective of protecting property loss, and OSHA’s concern is that efforts to prevent property loss do not endanger the safety of workers designated to fight the fires. Specific OSHA concerns for fire brigades are listed as follows along with associated annual citation activity as gathered from the NCM database: Organization and personnel fitness for firefighting: OSHA standard 29CFR1910.156(b)(2): 2 citations Firefighter training: OSHA standard 29CFR1910.156(c): 27 citations Maintenance and inspection of firefighting equipment, including respirators: OSHA standard 29CFR1910.156(d): 4 citations Protective clothing for firefighters: OSHA standard 29CFR1910.156(e): 7 citations Respiratory protection for firefighters: OSHA standard 29CFR1910.156(f): 2 citations Source: NCM database

13.47.

The appropriate OSHA standard for fire alarm systems, as determined from the OSHA website, is: OSHA standard 29CFR1910.165 – Employee Alarm Systems: Number of citations for the fiscal year: 69 citations Source: NCM database

CHAPTER 14

SOLUTIONS TO END-OF-CHAPTER EXERCISES

14.1.

Three legs of the four may be supporting the full weight at any given time, with the fourth leg being slack.

14.2.

Put all u-bolt clips on ropes with the saddle assembly on the live portion of the rope, instead of vice versa.

14.3.

The crane is unable to pick up an overload because the crane is equipped with a hoist motor that cannot develop sufficient torque to overload the crane.

14.4.

Warehouse space

14.5.

(b); the angle of the sling legs are closer to vertical. Orientation (a) would place more stress on the sling legs because the sling legs would be more horizontal to reach around the horizontal orientation of the load.

14.6.

LPS to a type DY: safer and therefore OK DY to LPS: LPS would not be authorized for Class III, Division I hazardous areas

14.7.

The normal status (neutral) of the spring-pushbuttons would maintain the position of the crane in event of a power failure and return of power.

14.8.

Mechanical advantage = 4 Rated load = number of parts of rope x (20%) x nominal breaking strength RL = 4 x 20% x 5000 RL = 4000 lbs 4000 - 200 = 3800 lbs (allowing for load block)

14.9.

A projection in front of the wheels on overhead bridge cranes that clears the rails of obstructions. It is needed to prevent the bridge truck (crane) from being derailed.

14.10.

(1) isolate or eliminate the in-running nip point (2) install guards (3) install emergency tripping devices

14.11.

So that the ladder will not be moved to another location while the crane is in use, thereby removing the operator's means of dismounting.

14.12.

Tampering with the design or altering the truck may invalidate the approval classification of the truck.

14.13.

Refer to the OSHA website to check OSHA standards under the general heading ―Material Handling and Storage.‖ Following are two example performance standards:

1910.176(a)

Use of mechanical equipment. Where mechanical handling equipment is used, sufficient safe clearances shall be allowed for aisles, at loading docks, through doorways and wherever turns or passage must be made. Aisles and passageways shall be kept clear and in good repair, with no obstruction across or in aisles that could create a hazard. Permanent aisles and passageways shall be appropriately marked. Note that the above wording does not specify exactly how wide an aisle should be to achieve ―sufficient safe clearances.‖ Also note that the standard calls for aisles to be ―appropriately‖ marked. The standard does not specify what constitutes ―appropriately marked.‖ 1910.176(b)

Secure storage. Storage of material shall not create a hazard. Bags, containers, bundles, etc., stored in tiers shall be stacked, blocked, interlocked and limited in height so that they are stable and secure against sliding or collapse. Note that the above wording does not specify a maximum height for stacking materials. The decision is left to the employer to keep height

limited to the degree necessary to prevent the hazards of sliding or collapse. 14.14.

Bridge--overhead cross-girder supporting the trolley Trolley--carries the hoist mechanism Pendant--hanging cord control Pulpit--fixed remote station for control Gantry--cranes which have legs which support the bridge above the railway Cantilever gantry--gantry cranes having extensions on one or both ends of the bridge

14.15.

(1) shorter wheelbase (which reduces stability) (2) small diameter wheels (3) poor visibility when loaded (4) ambient plant noise may prevent pedestrians from hearing an approaching lift truck

14.16.

(1) large mass--much larger masses than the human body (2) motion--the frequent movement of the large masses compounds the likelihood of injury (3) automatic or remote control nature--this contributes to the hazards by lack of local control of wide-ranging equipment such as conveyor belts and materials pumps (4) fire--hazards due to storage of materials

14.17.

Gross load

= payload + load block = 2000 + 100 = 2100 lbs

Wire rope load =

14.18.

Gross load

=

Mech. adv.

Number of parts of rope =

2100 3

= 700 lbs.

3

nominal breaking strength wire rope load

 5

Eqn. 14.5

nominal breaking strength  5 · (wire rope load)  5 · 700  3500 lbs 14.19.

Gross load

= payload + load block = 3000 lbs + 150 lbs = 3150 lbs

The problem states that the wire rope is "rated" at 2,000 lbs. The term "rated" implies that the safety factor of 5 has been applied and that Nominal breaking strength = 5 x "rating" = 5 x 2000 = 10,000 lbs Applying Eqn. 14.1: rated load nbr. of parts of rope

 20% x (nominal breaking strength)

3150/4 = 775  20% x 10000 lbs. Therefore the assembly as described meets standards. 14.20.

First, calculate the nominal breaking strength of the wire rope: Nominal breaking strength = 5 x "rating" = 5 x 2000 = 10,000 lbs Applying Eqn. 14.l: rated load nbr. of parts of rope rated load

 20% x (nominal breaking strength)

 (parts of rope) x 20% x (nom. brk. strength)

 4 x 20% x 10000 lbs.  8000 lbs Maximum payload

= rated (gross) load - load block 8000 lbs - 150 lbs = 7850 lbs

14.21.

Vertical component of force on each of three legs

= 1/3 x 1000 lb = 333 lb.

When a sling leg is 30 from horizontal, the tensile stress in the sling leg is twice the vertical component of force. Therefore, stress on each leg = 2 x 333 lb = 667 lb 14.22.

Let W represent the maximum total load the sling is rated to pick up. The problem is to find W. Weight borne by each sling leg = W/3 (This is the vertical component of force on each sling leg.) The tensile stress on each leg in the sling is limited to the rated load of the chain used in the sling, which was given in the problem as equal to 6 tons. Then: W/3

=

sin 60o x 6 tons

W

=

3(.866 x 6 tons)

=

15.6 tons

If the student does not have a background in trigonometry, the correct ratio (for sin 60) can be inferred from Figure 14.12(a), in which the sling leg angle is identical (60). 14.23.

If the trolley rides on top of the rail, the device is a crane and the safety standard for overhead and gantry cranes applies. If the trolley hangs from the lower flange, the device is an underhung crane or monorail, and the standard for monorails applies.

14.24.

Plugging is the use of the hoist motor in reverse as a braking mechanism. The OSHA standards do not prohibit plugging, but the crane operator should not use plugging to substitute for an inoperative brake.

14.25.

The hoist is the part of the lifting mechanism that lifts the sling and the payload. The sling is the flexible chain, wire rope, and other attachment that is used to wrap around or attach to the load so that the hoist can lift it.

14.26.

The more severe (acute) the leg angle is from the horizontal, the greater will be the stress on each leg of the sling. In quantitative terms, using trigonometry, Ts Ts

= V s / sin L Where, = tensile force on a leg of a sling

Vs

=

vertical (lifting) force exerted on the load by this leg of the sling

L

=

leg angle for this leg of the sling

As L approaches 90, the sin L approaches unity and Ts = Vs. As L approaches 0, the sin L approaches zero and Ts approaches infinity. Before Ts reaches infinity, of course, the sling will break. 14.27.

A sling that is too short will necessitate a very acute leg angle and thus will cause a severe stress upon the legs of the sling.

14.28.

Binding straps on a load are of the load. If the load is severe (acute) angle will be will be nearly horizontal at

necessarily tight to maintain the security picked up by the binding straps, a very formed by the tight binding straps that the attachment point. The severe angle

will cause an unusually high force on the straps, usually much greater than the entire weight of the load. The straps are likely to break, dropping the load.

14.29.

1. 2.

The in-running nip-point must be hidden (submerged) in order for the conveyor to operate. An operator often must stand or work close to the (hidden) intake of the screw conveyor in order to shovel or otherwise distribute material into the intake.

14.30.

Design a box or other enclosure around the conveyor intake. The box or enclosure must have openings in order for the conveyor to operate, but the openings can usually be made large enough for the conveyor to function, but small enough that a worker's hand, foot, or other body part will not intrude into the danger zone.

14.31.

If an overhead crane is positioned to pick up a load situated in a pit in the floor the crane line will be reeled out a greater distance than it would be for a lift from floor level. If the crane is designed to pick up loads no lower than the floor, then to reel out further to pick up a lower load would possibly reduce the number of wraps on the drum to a dangerous point. For safety, the allowable minimum for the number of wraps on the wire rope drum is two.

14.32

Lifting is very complex and injuries from lifting are caused by a variety of factors that are difficult to control. Examples are the geometry of the object to be lifted, the physical condition of the lifter, and the posture of the lifter. A rigid standard could hardly consider all of the factors and would be very difficult to enforce.

14.33

The greater the horizontal distance of the load from the lifter's body, the more difficult it will be for the lifter to manage the lift. Therefore, the maximum load the lifter can pick up is reduced (greatly) by this horizontal distance. The geometry of the load can greatly affect this distance.

14.34

When lifters lift with their legs, they are lifting not only the load but their entire body as well. In addition, it can be very awkward or difficult to position the load to lift it with the lifter's legs.

14.35

The hoist must be rated system we must consider solution we will assume load including the load to Eqn 14.1,

at 10 tons = 20, 000 lbs. In the design of the the weight of the load block, which for this a weight of 150 lbs. Therefore, the total rated block will be 20,150 lbs. Applying this amount

20,15 0  20% x nominal breaking strength of the rope n where n = the number of parts of rope 20,150  n Try n = 2: Try n = 3: Try n = 4:

20% x 30,000 lbs = 6,000 lbs

20,150/2 = 10, 075 (This is not  6000 lbs) 20,150/3 = 6, 717 (This is not  6000 lbs) 20,150/4 = 5,037.5 (This is  6000 lbs)

A mechanical advantage of 4 parts of rope will be required, which will necessitate two sheaves on the upper block and two on the lower block, as shown in the sketch.

14.36.

The design solution for this exercise takes a conservative approach by assuming that the walls, ceiling, and other surfaces along the aisles of the warehouse are black and do not reflect light. Thus the point source lamps provide the only illumination to the surface. The most poorly illuminated points along the aisles would be the floor points most distant from any lamp, i.e., those points halfway between adjacent lamps. The illumination of those points would primarily emanate from the two bulbs equidistant from two adjacent lamps. Although some light would also be provided by other lamps more distant from the point than the two adjacent lamps, this additional light will be ignored in this analysis to take a conservative approach to be sure that adequate light is provided. The illumination of point x from a given lamp in lumens per square foot is found by dividing the lumen output of the bulb by the area on the surface of a sphere of radius equal to the distance from the lamp to point x. The area of a sphere is 4r2. There will be a tradeoff between the lamp intensity and the spacing of the lamps. Selecting lamps capable of producing 8000 lumens each and assuming that illumination of the most distant point from two lamps would be equally illuminated by each of the two lamps, each lamp would be required to illuminate the point by 1 lumen per square foot (1/2 of 2 lumens per square foot). Therefore the area of the sphere of illumination would be 1700 square feet. Then and

8000 = 4r2 r = 25.23 feet

This radial distance would represent the hypotenuse of a right triangle in which one leg would be the ceiling height (20 ft) and the other leg would represent horizontal distance x (earlier defined) and half the horizontal distance to the nearest adjacent lamp. Thus, and

x2 + 202

=

25.232

x

=

15.38

The horizontal spacing between the lamps would then be 2 x 15.38 = 31.76 feet. A spacing of any amount less than 31 feet should be adequate. To be conservative, a spacing of 25 feet should provide some margin for error. 14.37.

The proposal to place a toggle switch control box on the wall raises some safety considerations that should be communicated to the design team. One concern would be the toggle switches. Crane controls should be of the ―deadman‖ type, which, if released, will stop crane movement. Another consideration is the placement of the control in a fixed position on the wall. An overhead bridge crane will travel some distance away from the control box on the wall. A better design would be a pendant control on a flexible cord that will travel with the bridge and trolley, placing the crane operator in closer proximity to the hoist. Another consideration would be the capability to lock out the control for maintenance. No mention was made of lock-out capability in the proposed toggle switch box to be mounted on the wall. The hazards from failure to lock out a crane during maintenance are aggravated by the distances which a crane can travel away from a fixed, wall-mounted control.

14.38.

The answer to this question will vary depending upon the level of current research in this area at the time of search on the Internet. As of this writing (mid-2003) 16 hits were returned for a search of the following keyword phrase: NIOSH lifting limits simulation virtual reality

CHAPTER 15

SOLUTIONS TO END-OF-CHAPTER EXERCISES

15.1.

That part of the machine where the tool engages the work.

15.2.

(1) Point of operation, (2) Power transmission, (3) In-running nip points, (4) Rotating or reciprocating machine parts, (5) Flying chips, sparks, or parts. The point of operation is the most important from a safety standpoint.

15.3.

(1) Where belts contact pulleys, (2) Where gears mesh, (3) Where mating rollers make contact

15.4.

(1) Guarding "by location" is positioning the machine or operation so as to position the dangerous parts where no one will be exposed to the danger, (2) Guarding is "by distance" when the size of the material or the nature of the operation does not require the operator to get close to the danger.

15.5.

A lockout is the use of a lock on an on-off switch or control box to prevent use of a machine while the machine is down for repair or maintenance. An interlock is an electrical circuit which prevents operation of a machine under certain circumstances, such as "enclosure not in place" or "gate open."

15.6.

The nylon is more susceptible than metal to the buildup of oil and lint which decreases the efficiency of the fan. Any fan guard (including nylon mesh) will decrease fan efficiency.

15.7.

S.D. = .333 sec x 63 in/sec = 21 in

15.8.

S.D. =

15.9.

The holes are for the purpose of anchoring a machine (1) for ease of shipping, (2) for security purposes, or (3) because the machine is designed for use in a "fixed location."

15.10.

(1) Gates, (2) Presence-sensing devices, (3) Pull-outs or pullbacks, (4) Hold-outs or restraints, (5) Two-hand controls, (6) Two-hand trips.

15.11.

An interlocked barrier guard has an interlock which disables the machine's actuating mechanism whenever the guard is opened. It is not intended for manual feeding. A gate opens and closes with each machine cycle and is a permissible safeguarding method for manually-fed power presses.

15.12.

Two-hand controls will stop the machine if they are released prematurely. Two-hand trips cause the machine to complete one cycle regardless of release time.

15.13.

Type A gates close before the press stroke is initiated and remain closed until all motion of the ram has ceased. Type B gates close before the press stroke is initiated but open after completion of the downward stroke, allowing the operator to reach in before motion has ceased. The Type A gate is the safer of the two.

15.14.

Allen-head screws make the removal of the machine guard more troublesome. The machine operator is less likely to remove it than if the machine guard is secured by wing nuts.

15.15.

Yes (from Table 15.1)

15.16.

An "awareness barrier" is a device to remind the operator that his/her hand or some body part is in danger. A "jig guard" has the function of both protecting the operator and facilitating the operation to increase productivity. The jig guard usually is designed to hold the workpiece in the correct position for operations to be performed upon it.

15.17.

A full-revolution press clutch will cause the crankshaft and flywheel to make one complete revolution together. A part-revolution press clutch typically has a friction clutch which can be engaged or disengaged at any point in crankshaft cycle, permitting the ram to be stopped at any point. "Part revolution" type is safer.

60/90[1/2 + 1/14] x 63 = 24 in

15.18.

"Muting" is the process of bypassing a presence-sensing device. Muting is permitted on the less-dangerous upward portion of the press stroke and thus can be used to make the operation more efficient by permitting the feeding of the dies during the upward stroke. A muted presencesensing device is analogous to a Type B gate, whereas an unmuted presence-sensing device is like a Type A gate.

15.19.

Galvanized wire mesh is more durable because the junctures of the wire crossing each other are held together by the fused galvanizing metal. Thus, personnel are less likely to penetrate or distort the guard mesh and encounter the danger zone.

15.20.

The need for proper adjustment due to variations in operator's body part sizes or variations in press setup--especially variations in die sizes.

15.21.

"Pullbacks" pull the operator's hands out of the danger area as the ram makes its downward stroke. "Restraints" do not allow the operator's hands to enter the danger zone at any time.

15.22.

Safety distance = 0.37 seconds x 63 inches/second = 23.31 inches

15.23.

At a minimum distance equal to the answer of Question 15.22.

15.24.

Safety distance

= 60/rpm(1/2 + 1/N) x 63 = 60/60(1/2 +1/4) x 63 = 47.25 inches

15.25.

No, the machine has a full revolution clutch and the ram cannot be stopped by the two-hand control. Presence-sensing devices are illegal for full-revolution presses.

15.26.

(1) Failure to keep the workrest in close adjustment (within 1/8 inch) to the wheel on offhand grinding machines. (2) Failure to keep the tongue guard adjusted to within 1/4 inch. (3) Failure to guard the wheel (including bolt end and flange) sufficiently. All three of these rules are aimed at protecting the worker in the event of a breakup of the wheel or preventing the breakup of the wheel. Grinding wheel breakup can result in worker fatality.

15.27.

If the die opening is less than ¼ inch, then the die itself meets the guard opening dimensions specified in the OSHA standard (see Table 15.1). By this same reasoning, the OSHA standard explicitly exempts all mechanical power presses having less than ¼ inch maximum die opening from the point-of-operation safeguarding requirements.

15.28.

Kickback is more likely and is a greater hazard for ripsaws than for crosscut saws.

15.29.

The "ring" test is to determine if a grinding wheel is cracked. The wheel is tapped with a non-metallic object. A good wheel will ring whereas a cracked wheel will sound dull.

15.30.

Compressed air hoses can cause hazardous flying chips. Also, compressed air at ordinary shop air pressures can even cause fatalities if introduced into the body through horseplay, experimentation, or carelessness. Workers should be taught to exercise care not to hold the compressed air nozzle against their skin or any part of their bodies. Compressed air is permitted for cleaning at pressures of 30 psi or less and then only with chip guarding or personal protective equipment. Even air pressures of 30 psi can be dangerous to the body.

15.31.

Shaft couplings need no guards when bolts, nuts, and setscrews are countersunk so that no hazardous projections are present. It is further desired that such fasteners be used parallel to the shafting.

15.32.

1 1/2 inches (from Table 15.1)

15.33.

Most of the citations have been procedural: 1. Failure to establish a program for lockout/tagout. 2. Failure to train employees for lockout/tagout. 3. Failure to document procedures for lockout/tagout.

15.34.

A disconnect switch or circuit breaker can be placed in series with the pushbutton on/off switches to disable the machine and nullify the effect of a normal pushbutton start switch.

15.35.

Guarding "by location" is positioning the machine or operation so as to position the dangerous parts where no one will be exposed to the danger. Guarding is "by distance" when the size of the material or the nature of the operation does not require the operator to get close to the danger. The two methods of guarding pertain to entirely different situations.

15.36.

Even when turned off, a machine can retain dangerous quantities of kinetic or potential energy. It is even possible for a machine to operate somewhat when it is turned off, running on the residual energy in a rotating flywheel, for instance. A procedure to place a machine in "zero mechanical state" not only turns off the power sources, but also removes all residual forms of energy so that the machine is incapable of actuating any of its parts even if there is some failure or inadvertent actuation of part of the machine.

15.37.

An "energy isolation device" is more than a switch; it is a switch that must be capable of being locked off.

15.38.

Flying chips, sparks, or parts.

15.39.

The General Fail-Safe Principle

15.40.

The best color is usually black. The point of operation is where the machine does the work, and an operator often must be able to see into the machine at this point. If the guard is painted orange or some other bright color, it inhibits the operator's ability to see into the point of operation.

15.41.

Hand-feeding tools or tongs facilitate the process and enhance safety by removing the need for operators to place their fingers or hands into the danger zone for the purpose of feeding the machine. However, the hazardous area is still exposed, and if for any reason operators choose to reach into the danger zone without the hand-feeding tools, they are exposed to the hazard. Even with the hand-feeding tools, it is possible for operators to place hands or fingers inside the danger zone. For these reasons, hand-feeding tools or tongs do not qualify as methods of "safeguarding the point of operation."

15.42.

Fixed barrier guard Adjustable barrier guard Die enclosure guard Interlocked barrier guard

15.43.

Die enclosure guards have the advantage of being small and close to the operation of the machine, making them efficient and convenient. They can be specially designed to fit the particular die's operation. Fixed barrier guards must accommodate all die configurations that might be mounted on the machine at various times or for various setups. They are necessarily large and, for some operations, awkward. The advantage of the fixed barrier guard, however, is that one guard is suitable for all operations and setups.

15.44.

The following possibilities are listed in the order of their seriousness: 1. The part will be damaged or ruined. 2. The die itself (much more expensive) will be ruined. 3. The operator will be injured by flying broken pieces of the product part or the die.

15.45.

Holdouts or restraints

15.46.

Type B gates are legal on full-revolution presses, but they are somewhat more hazardous than a Type A gate or other more positive methods of keeping the operator's hand out of the danger zone. The extra hazard introduced by the Type B gate is that it allows the operator to reach in during the upward (less hazardous) part of the stroke. But during the upward stroke the ram of a full revolution press is still engaged mechanically to the flywheel. If there is a failure of the engagement mechanism to disengage, the ram can, and sometimes does, execute a repeat stroke.

15.47.

The primary advantage of the friction clutch is that it enables the press ram to be disengaged from the flywheel at any point in the stroke, in the event of an emergency or a reach into the danger zone midstroke. Another advantage is that the friction clutch can speed up production in to ways: (1) it can permit the operator controls to be safely located closer to the point of operation, and (2) it can engage the flywheel immediately for a quicker initiation of the downward stroke.

15.48.

Type A gates on part revolution presses: (Unless the press safeguarding system is inspected weekly). The type A gates close before initiation of the downward stroke of the ram and stay closed until the motion of the ram has ceased (after completion of the upward stroke). Type B gates on part revolution presses: (Unless the press safeguarding system is inspected weekly). They close before initiation of the downward stroke, but they reopen again during the upward stroke. For the Type B gate setup, the brake monitor and control system must detect top-stop overrun beyond limits. Presence sensing devices on part revolution presses: They interrupt the actuation of the ram mid-stroke if the operator or anything else intrudes upon the protective screen. Two-hand controls on part revolution presses: They require both hands of the operator to be safely outside the danger zone to concurrently hold the buttons or other controls to actuate the ram during the entire stroke. Two-hand trips on part revolution presses: They require both hands of the operator to be safely outside the danger zone to concurrently press the buttons or other tripping mechanisms to initiate action of the ram stroke. It should be recognized that a two-hand trip setup is unusual for a part-revolution press. The two-hand trip mechanism does not take advantage of the press's capability of being stopped mid-stroke. Although not expressly illegal in the OSHA standards, a two-hand trip on a part revolution press would necessitate using the Safety Distance formula for two-hand trips with an infinite number of engagement points. Although such a set-up would be a slight improvement over a full revolution press with a finite number of engagement points, it would be both safer and more efficient to employ two-hand controls that could take advantage of the clutch and brake to stop the ram midstroke. Such an arrangement would permit the use of the safety distance formula for two-hand controls and would result in a closer and more efficient placement of the control station.

15.49.

Type A gates: They close before initiation of the downward stroke of the ram and stay closed until the motion of the ram has ceased (after completion of the upward stroke). Presence sensing devices (only on part-revolution presses): They interrupt the actuation of the ram mid-stroke if the operator or anything else intrudes upon the protective screen. They do not qualify for full revolution presses, because the actuation of the ram on full revolution presses can not be interrupted. Pullbacks: They pull the operators hands and fingers out of the danger zone as the ram stroke is initiated in the event that the operator has not already removed them. Restraints: They are not legal for handfeeding without tongs or handfeeding tools because they are designed to keep the hands and fingers out of the danger zone all of the time. Two-hand controls: They require both hands of the operator to be safely outside the danger zone to concurrently hold the buttons or other controls to actuate the ram during the entire stroke. Two-hand trips: They require both hands of the operator to be safely outside the danger zone to concurrently press the buttons or other tripping mechanisms to initiate action of the ram stroke.

15.50.

This design case study uses the principle of the safety distance formula to set design parameters for the design of the engagement mechanism for the flywheel. Using Eqn 15.2, let D represent safety distance: D = 60/rpm [1/2 = 1/N] x 63 [1/2 + 1/N] =

[ Dx rpm] [60 x 63]

[D x rpm] [60 x 63]

1/N =

-

1 2

For rpm = 100 and D = 20 inches:

 20 x 100   60 x 63   

1/N =

N

=

.529

=

.029 =

-

-

1 2

.500

34 engagement points

15.51.

Muting. Muting disables the presence-sensing system during the upward portion of the ram stroke. Likewise, for gates, the difference between Type A and Type B is that for Type B the gate system is disabled on the upward portion of the ram stroke.

15.52.

A brake monitor is installed on a press permanently to monitor the slippage and wear of the brake by checking stopping time or flywheel overtravel on every stroke of the press. A brake stop-time measurement device is a portable instrument taken from press to press to check stopping time for the purpose of setting safety distances for two-hand controls and presence sensing devices.

15.53.

First, infrared light sensors are not subject to inadvertent tripping by ambient light in the visible spectrum. Second, infrared light is invisible and this feature has some advantage in not revealing to the operator the means of operation of the sensor.

15.54.

Tripping of the top-stop overtravel limit switch means that the brake has deteriorated beyond limits. Therefore, the brake monitor provides an indication to that effect. In addition, the brake monitor signals the control system to disable the press such that it will cease to operate. However, the control system will not disable the brake system of the press.

15.55.

The advantage of adjusting the overtravel limit switch high is that it gives the machine greater tolerance to brake wear. As the brake deteriorates, the machine will continue to operate instead of becoming disabled by the brake monitoring and control system. The advantage of adjusting the overtravel limit low is that a lower overtravel limit controls the press to a shorter stopping time, which means that the press control can be placed at a shorter (closer) safety distance, which means increased efficiency.

15.56.

On a handheld saw, the blade is very dangerous if the saw is set down or dropped either before or after the cut. Before the cut, the blade is brought up to rotational speed, and after the cut, the blade will continue to rotate for a time after the trigger is released. Without the retractable guard, the handheld saw would be very hazardous at these times. Particularly AFTER the cut the operator would be tempted to set the saw down somewhere before waiting for friction to slow the blade to a complete stop.

15.57.

Required features: spreaders and nonkickback fingers (or ―dogs‖). The spreaders keep the saw kerf open or spread apart in the completed portion of the cut so that the material will not contact the blade. The nonkickback fingers are designed to arrest the kickback motion should it start to occur.

15.58.

Fixed barrier guards encompass the entire die area and accommodate various size dies. Therefore, they are more distant from the point of operation and permit larger openings through the guard, provided that OSHA requirements are met with regard to the distance to the danger zone and the maximum opening size of the guard mesh.

15.59.

A power hacksaw and a bandsaw are used for similar purposes. Both have a thin, narrow (band-type) blade. However, the hacksaw uses a reciprocating motion, and the bandsaw uses a continuous motion with a blade that is a continuous loop. The hacksaw is more difficult to guard because the guard must continually adjust back and forth to the work during every stroke of the blade.

15.60.

The footswitch may be convenient for quick actuation of the press to permit higher production rates. The presence-sensing device acts as the safeguarding mechanism in case an operator places his or her hands within the danger zone.

15.61.

The disadvantage of awareness barriers is that they do not really prevent the operator from reaching into the danger zone. They seem to act as a guard but may lure the operator into a false sense of security. Also, some awareness barriers contribute to the problem by obscuring vision of the real danger zone.

15.62.

Type A gates keep the gate closed until all motion of the ram ceases. Type B gates permit the gate to open during the less hazardous upward portion of the stroke, which speeds up the operation and improves efficiency. ―Muting‖ is a design feature of presence-sensing devices that permits the sensing device to be ignored during the less hazardous upward portion stroke with production advantages identical to those of the Type B gate.

15.63.

(Author’s note: Exercise 15.63 is the same as Exercise 15.53.) One advantage is that the infrared light sensors will not incorrectly sense stray ambient light around the workstation. Another advantage is that the infrared light is invisible to the operator; this can be an advantage as the operator will not be aware of the mechanism by which sensor is operating, and thus it will be more difficult for the operator to defeat the protective system.

15.64.

The safety of control pedestals for punch presses is dependent upon their positioning at an adequate safety distance from the point of operation, depending upon the design of the press and the stopping time of the ram. OSHA standards require the pedestals to be bolted to the floor, once they are adjusted to the prescribed safe distance. Otherwise, workers may be tempted to move the pedestals closer to the machine to facilitate feeding and operation of the press and thus speed up production.

15.65.

The speed of the ram of a punch press is directly related to its momentum or inertia. A part revolution press has a clutch and brake, and this system must overcome the inertia of a high-speed ram and bring the ram to a stop if safety requires it. Therefore, if the press is of part revolution design, fast rams are more dangerous than slow ones. However, if the press is of full-revolution design, it is recognized that the ram can not be stopped mid-cycle. Safety for the fullrevolution design is dependent upon the ram finishing its cycle before the operator can reach into the danger zone. For such designs safety is enhanced by speeding up the press so that the ram can close more quickly. This greater level of safety is recognized in the OSHA standard formula for the computation of safety distance from the point of operation for the placement of controls and safeguarding devices.

15.66.

This design case study requires the application of the principle of the safety distance formula to design the system to accommodate safe ranges of operation of the flywheel to facilitate the safe operation of the safeguarding system. From Eqn 15.2, let D represent safety distance: D = D = D = rpm

60/rpm [1/2 + 1/N] x 63 60/rpm [1/2 + 1/2] x 63 60/rpm x 63 = [60 x 63] /D

For a safety distance of 16 inches: rpm = [60 x 63] /16 = 236 rpm (as a minimum) A slower flywheel speed would lengthen the time required for the dies to achieve complete closure, giving the operator more time to reach in and be endangered by the closing of the dies. 15.67.

Alternative design #1: (Least expensive) The Type A gate could be replaced with a Type B gate. The Type B gate would speed up the operation by permitting the gate to open during the less hazardous upward portion of the stroke. By opening the gate sooner after the downward stroke, the operator could have access to the danger zone for unloading the point of operation and reloading it for the next cycle. However, because of the possibility of a malfunction resulting in an

accidental repeat stroke, the Type B gate increases the hazard somewhat and should be avoided if possible. Alternative design #2: Convert the press to a part-revolution design by equipping it with a clutch and brake. Although more expensive than alternative #1, the clutch and brake would promote safety and permit the use of two-hand control systems that are safely positioned closer to the point of operation. The close placement would facilitate feeding and speed up production while safety is preserved by the superior control of the ram stroke afforded by the clutch and brake. Alternative design #3: (Most expensive) Same as alternative #2 above, only replace the two-hand control with a presence-sensing device for safety and use a footswitch tripping mechanism. The presence sensing device could be muted on the upward stroke for maximum efficiency. Alternative #3 would maintain safety using the clutch and brake system to stop the press in the event the danger zone is violated. Maximum safe access to the danger zone for feeding, made possible by the footswitch freeing the hands from the responsibility for tripping, would make this arrangement the most efficient. 15.68.

If there are only 14 available engagement points on the machine (some actual press models have exactly 14 engagement points), something would have to be changed to make the press safe. The control station could be moved slightly further away according to the safety distance formula (Eqn 13.2, page 316) as follows: D = [60/100] x [1/2 + 1/4] x 63 = 21.6 inches Another solution would be to slightly increase the speed of the flywheel. Solving Eqn 15.2 for rpm: D x (rpm) = 60 x [1/2 + 1/N] x 63 rpm = 60 x 63 x [1/2 + 1/N] / D For this situation: rpm rpm

=

60 x 63 x [1/2 + 1/14] / 20 =

108

Another solution (the best solution) to the problem from the safety perspective would be to retrofit the press by equipping it with a clutch and brake so that it would operate as a part revolution press. Fully equipped with a brake monitoring and control system the remodeled part revolution setup would permit an entirely different formula for safety distance that would be based upon the stopping time of the press. STANDARDS RESEARCH QUESTIONS 15.69.

The general machine guarding standard, which includes point of operation guarding, is very frequently cited. A more specific standard for point of operation guarding is 29CFR1910.212(a)(3)(iii). OSHA cites either standard for failure to guard the point of operation. There are other OSHA standards pertaining to point of operation safeguarding for specific machines, for example mechanical power presses. (See Exercise 15.70). Following are frequency of citation fiscal year statistics for the general point of operation standards (source: NCM database): 212(a)(1): 212(a)(3)(iii): Total for these 3 standards

2675 21 2883

Source: NCM database

According to the OSHA website, OSHA standard 1910.212(a)(1) was the seventh most frequently cited standard for Fiscal Year 2001-2002, all OSHA standards considered (general industry, construction, etc.). This fact was found by searching the OSHA website with the term ―frequently cited standards.‖ The statistics may change from year to year, but point of operation guarding for machines has remained a consistently frequently cited standard over the years. 15.70.

For power presses the point of operation guarding standard is

29CFR1910.217(c)(1)(i). This standard is frequently cited among the provisions of the power press standard, but because the scope of the power press standard is limited, 217(c)(1)(i) is not as frequently cited as the point of operation provisions of the general machine guarding standards. Following are frequency of citation fiscal year statistics for the power press point of operation guarding standard: 217(c)(1)(i):

187 citations Source: NCM database

15.71.

The OSHA website identifies the general abrasive wheel standard as 29CFR1910.215. Searching the NCM database by standard number, entering the search field 215* the following provisions for the standard were found to be the top three most frequently cited standards in the abrasive wheel standard. Citation frequencies were found for Fiscal Year 2001-2002: (the text for the standards is summarized from the full text found on the OSHA website): 215(b)(9) – Exposure adjustment (of the ―tongue‖ guard within ¼ inch of the wheel). citation frequency: 1980 citations 215(a)(4) – Work rest (adjustment of the work rest within 1/8 inch of the wheel) citation frequency: 1270 citations 215(a)(2) – Guard design (guard shall cover the spindle end, nut and flange) citation frequency: 235 citations Source: NCM database

CHAPTER 16

SOLUTIONS TO END-OF-CHAPTER EXERCISES

16.1.

1) Gas welding, (2) Electric-arc welding, (3) Resistance welding. Resistance welding is the cleanest and most healthful.

16.2.

Welding occurs when the material that melts is either the material to be joined or a like material. Brazing and soldering are done by melting some other material with a lower melting temperature than would be required for melting the metals to be joined.

16.3.

When the melting material has a melting point above 800F, the process is brazing; below 800F, the process is soldering.

16.4.

Stick electrode welding (common name) shielded metal arc welding (SMAW); this is the designation used by the American Welding Society.

16.5.

GTAW--gas tungsten arc welding GMAW--gas metal arc welding SAW--submerged arc welding RSEW--resistance seam welding RSW--resistance spot welding

16.6.

To prevent liquid acetone from entering the valve passages. The acetone could be ignited accidentally and is quite dangerous.

16.7.

Oxygen is almost completely inert if it is kept away from fuel sources. Acetylene is very unstable and must be stored at low pressures to prevent spontaneous explosion.

16.8.

Workers often hold their hands over the valve opening when first opening the valve to test the cylinder. If a greasy glove is on that hand, the presence of pure oxygen causes the grease to become explosively combustible.

16.9.

Production costs can be cut in some applications by using an alternate gas to replace the more dangerous and expensive acetylene fuel gas. This can be done only if material to be welded has a low enough melting point for the alternate gas to accommodate.

16.10.

Valve protection caps protect the valve from damage. The slots in the cap allow escaping gas to escape in a manner which will prevent the cylinder from becoming a missile. The slots are misused by workers who insert pry bars into the slots for extra leverage in handling the cylinders.

16.11.

Flashback is a phenomenon in which the welding flame travels back up the mixture stream, burning inside the torch.

16.12.

Tape may hide defects in the hose.

16.13.

Copper, because acetylene reacts with copper to produce copper acetylide, a dangerous explosive.

16.14.

Many of the small arc welding machines weld at higher voltage than do the industrial type welding machines. These smaller machines achieve power by making up in voltage what they lack in current flow. These larger voltages can overcome electrical resistance to produce dangerous electrical shock when careless use causes exposure to the welder.

16.15.

The welding cable carries so much current that it overheats easily. Coiling the cable increases its resistance, causing higher temperatures than uncoiled cables.

16.16.

If the metal tank contains compressed gas, the high amperage of the welding circuit could cause the heat buildup in the tank, possibly causing the pressure limit of the tank to be exceeded.

16.17.

The submerged arc welding process (SAW) is gaining in popularity because the arc is hidden from view by the puddle of molten welding materials, making arc radiation protection unnecessary. The welding flux used in SAW is a granular type (like sand) which is continually added to the weld. This makes welding overhead impossible or extremely awkward--a big disadvantage.

16.18.

The point of contact where the spot weld is made is analogous to a power press.

16.19.

(1) Short duration of the hazard, (2) People do not realize the ignition potential of welding. (The ignition potential is unfamiliar to most because they are not accustomed to watching welding operations because of the eye hazards.)

16.20.

Fires and explosions

16.21.

SMAW (shielded metal arc welding), commonly called ―stick electrode welding,‖ needs the most eye protection. The principal eye hazard to welders is exposure to the high energy of the bright light rays produced by the arc. SMAW without eye protection causes severe exposure to the bright light of the arc. Do not be confused by the term ―shielded‖ that forms part of the name of this process. ―Shielded‖ refers to oxidation protection afforded by the sheath of flux that surrounds the metal weld material in the welding ―rod.‖ The other two processes, SAW and RSEW protect the welder from such exposures to welding rays in quite different ways. In the case of SAW (submerged are welding) the arc is hidden beneath a puddle of welding flux that starts as a granular solid and melts during the process to submerge the arc. The arc thus submerged is protected from oxygen exposure, which protects the weld; at the same time the welder’s eyes are protected from exposure to the dangerous rays. In the case of RSEW (resistance seam welding) the welding heat is produced by electrical resistance and pressure between the two sheet metal surfaces to be joined by a seam. This welding heat does not produce a visible arc, so welding rays from the arc present no dangerous exposure to the welder. This is not to say that no eye protection at all is needed for SAW or RSEW welders. There are hazards to the eyes other than the radiation from the welding arc.

16.22.

Leather

16.23.

"Siderosis"--It is not a severe hazard by itself.

16.24.

There are so many variables to measure. The welding fume contains tiny, transitory concentrations of trace compounds that are difficult to capture and analyze, both quantitatively and qualitatively.

16.25.

Welding "fume" is the re-condensed particulate from extremely hot metal vaporization. Toxic gases are true gases released from chemical reactions among the weld flux, the air, the welding fuel, the weld metal, surface coatings or other materials present at the weld.

16.26.

The coating or condition of the surfaces to be joined or the solvent used to clean the surfaces may result in the release of toxic gases during the welding process. Inadequate ventilation could increase the hazards.

16.27.

HAZARD 1: Acetylene cylinders should be stored valve end up. The liquid acetone inside the tank could be passed through the valve if the cylinder is lying on the floor. HAZARD 2: together.

Oxygen and acetylene cylinders should not be stored Fire hazard.

HAZARD 3: Manifold pressure for acetylene is too high. unstable at pressures greater than 30 psig.

Acetylene is

HAZARD 4: The nail-polish remover odor is obviously due to leaking acetone, a very flammable and hazardous substance. HAZARD 5: The greasy gloves are an explosion hazard in the vicinity of oxygen, especially when the oxygen valve is opened by the welder wearing the greasy gloves. HAZARD 6: The welder should not use his torch tip to chip slag from the finished weld. The tip could be damaged, resulting in flashback. HAZARD 7: The welding hose should not be completely wrapped with tape, possibly concealing breaks or defects in the flexible hose. 16.28.

The term "gas welding" implies that the source of heat is from burning a gaseous fuel. Nitrogen is not a fuel gas and has a different function in the welding process in that it acts as an inerting agent.

16.29.

Normal atmosphere is approximately 78% nitrogen (ref p. 175 of the text). Converted to parts per million:

PPM

=

percent x 10,000

=

78%

x

10000

=

780,000 ppm

Obviously, nitrogen is not a toxic substance, but if it is present in the air at concentrations much higher than 78% it can act as a simple asphyxiant by crowding out essential oxygen. Oxygen deficiency is a serious hazard resulting in many fatalities every year. 16.30.

Acetylene is normally dissolved in acetone while in storage and is thus much more stable than in its free gaseous state. In addition, the acetylene cylinder is typically filled with a porous solid material which suspends the acetone/acetylene solution and protects it from shock pressure.

16.31.

1. Extremely high pressure is contained within an oxygen cylinder (approximately 2000 psi). Respect for this pressure demands that the valves be protected with caps when the cylinder is not connected for use and that the cylinders themselves not be misused. 2. Fire hazards are exacerbated by oxygen-rich atmospheres especially when the oxygen is under pressure. Greasy gloves ignite explosively when oxygen cylinder valves are opened and checked manually by the welder.

16.32.

MAPP gas and natural gas can sometimes be used as alternative fuels for acetylene. The disadvantage is that these fuels do not burn at temperatures as hot as does acetylene.

16.33.

Welding hazards are easily subject to exaggeration on one hand or understatement on the other. Many very dangerous gases are released in the process of welding materials that are both widely varying and under temperature extremes. These very dangerous gases, such as phosgene (chemical warfare gas) can be terrifying to consider in a work environment. The key to controlling paranoia about welding hazards is to recognize that the quantities and concentrations of these dangerous gases is quite low. Air contaminants can be controlled by exhaust ventilation or by personal protective equipment or both. With proper protection from hazards welders can live long lives despite the deadly gases that are produced by their work. Epidemiological studies have shown that welders will not necessarily die young. On the other hand, welding hazards are often overly minimized because their acute effects might be mild, or at least tolerable. Welding gives rise to serious hazards that are insidious in their attack. Minute exposures may result in minimal acute effects, and welders may simply ignore the hazards as a result. The insidious nature of the health hazards is that many of the contaminants slowly take their toll over the years, resulting in serious illness or even death long after exposure. Therefore, the wise Safety and Health Manager will take welding hazards seriously and not minimize their importance even though nausea, dizziness, or other acute symptoms may not be present.

16.34.

Phosgene

16.35.

―Monday morning sickness‖ is a suspicious condition, raising speculation that a worker may be malingering or attempting to extend a weekend for personal activities. If the worker is a welder, however, there is a genuine, medical reason for the worker to become sick on Mondays more than on other days. Exposure to zinc fume and some other metal fumes gives rise to ―metal fume fever.‖ Daily exposure to metal fume results in a sort of immunity, but this immunity can be lost in just a few days away from exposure. Thus, on a weekend a welder can lose immunity to metal fume fever and become sick upon returning to work and exposure to metal fume on Monday.

16.36.

The principal hazard from exposure to welding flux during welding operations is in elemental fluorine or fluorine compounds becoming airborne and contaminating the breathing atmosphere. As with many other welding air contaminants, the hazardous exposure effect is chronic, not acute. Therefore, the hazard may go unnoticed until the long term damage is done. Long-term exposure can cause abnormalities in the victim’s bones.

RESEARCH EXERCISES 16.37.

Nitrogen and oxygen are very complex in the ways the atoms form bonds to make compounds. Four different compounds make up the classification NOx. They are: N2O Nitrous oxide, commonly called ―laughing gas‖ and formerly used as dental anesthetic. N2O is associated with the mildest hazards among the compounds of the NOx family. It is listed as ―slightly dangerous‖ by Sax (see reference below) and has both health and safety hazard implications. NO

Nitric oxide.

NO2

Nitrogen dioxide.

N2O5

Nitrogen pentoxide.

Except for N2O, the hazards of NOX are quite serious and even insidious in their nature. The term ―insidious‖ is used because of the mechanism of their attack on the body. NOx is only slightly soluble in water, so the acid they produce (nitric and nitrous acid) does not irritate the mucous membranes as much as they would if the solubilities were greater. This would seem to be good, but unfortunately, the warning property of the irritation is reduced in effect and the exposure goes unnoticed. Without serious irritation, exposure continues and acids form deep within the respiratory system, sometimes with disastrous effects. An excellent source for reviewing these effects are the various editions of the classic reference by Sax. The version used by this author is: Sax, N. Irving. Dangerous Properties of Industrial Materials, 5th edition, New York: Van Nostrand Reinhold Company, 1979. All four of the oxides of nitrogen are both health and safety hazards, to varying degrees. The safety hazards are explosion, fire, and violent reactions with common materials. The health hazards are highly toxic gases formed during decomposition from heating and reaction with common materials, even water. 16.38.

An Internet search using such keywords as ―disaster,‖ ―fire,‖ and ―welding‖ will be the start of a search into dozens of interesting sites. One outstanding example that students may be familiar with from media reports is the Indianapolis fire that burned 10 floats in May, 1997, before the Indianapolis 500 Festival Parade. Many students may remember that disastrous fire that destroyed 10 floats and caused $1 million damage to the company (ExpoDesign) that builds the floats. What many may not remember is that the fire was caused by a welder’s torch. Many other disastrous welding fires can be found in media reports.

16.39.

This research question could evolve into a term paper project for a student. On the Internet try either of the following sites for starters: http://www.amweld.org http://www.aws.org Example types of information available include: book titles, visual aids, welding products buyers’ guides, manufacturer names, journal subscription information, information on welding inspection, scholarship opportunities, certification information, conference and convention calendars, membership information, welding schools information, career advertisements, welding standards information, government affairs, answers to technical questions, and local chapter information.

STANDARDS RESEARCH QUESTIONS

16.40.

The reader should go to the OSHA website on the internet and activate the link to ―standards‖ under ―Laws and Regulations.‖ Then select the link to Part 1910. A text search capability is then displayed, and an excellent search term for this exercise is the term ―noncombustible barrier.‖ This search term will zero in on the general industry standard 1910.253 and the corresponding construction industry standard 1926.350. Select the general industry standard, 1910.253. Upon display of the full text of the standard, use edit to perform a search within the text of the standard, again using the search term ―noncombustible barrier.‖ The search will jump immediately to the standard in question, 1910.253(b)(4)(iii). The NCM database can then be searched for this particular provision of the general industry welding standard to determine the frequency of citation of this provision. For the Fiscal Year this provision of the standard was cited 621 times.

16.41.

From searching the OSHA website within the OSHA Part 1910 General Industry standards, it can be determined that the principal standard for gas welding is 29CFR1910.253 and the principal standard for arc welding is 29CFR1910.254. The NCM database can be used to gather summary data on the citation of all of the provisions of each of these standards. For frequency of citation the comparison is as follows: 1910.253

1400 citations in the Fiscal Year

1910.254

254 citations in the Fiscal Year

It is apparent that OSHA finds many more citations of the gas welding standard than it does for the arc welding standard.

CHAPTER 17

SOLUTIONS TO END-OF-CHAPTER EXERCISES

17.1.

Fire and electrocution

17.2.

approximately 500 to 1,000

17.3.

Although 220-volt and 440-volt circuits have a higher potential for delivering a fatal amperage than does a 110-volt circuit, the 110-volt circuit can deliver a fatal amperage. The common use of 110-volt circuits has led to a complacency with 110-volt circuits which causes the hazards of 110-volt circuits to be greater than that of the higher voltage circuits.

17.4.

At 70 milliamperes or greater (Figure 17.1)

17.5.

Grounding is the return section in a complete electrical circuit. Equipment must be grounded to protect a worker in case of a "short" to the equipment casing.

17.6.

The "hot" wire provides contact between the power source and the load using electricity. The "neutral" wire is the normal completion of the circuit providing a path for the current to ground. The "ground" wire is a safety device which is the ground wire in case of a short from the hot wire to the casing (or other conductive part of the load being used). This low resistance circuit will "blow" a fuse or "trip" a breaker to open the circuit.

17.7.

GFCI is abbreviation for "ground fault circuit interruptor" which is a safety switch to open a circuit that has a partial short to ground that is insufficient to "trip" a circuit breaker. The short is revealed by detecting a tiny current imbalance between the flows of the hot and neutral wires. The GFCI is commonly used on construction sites.

17.8.

Double insulation is an extra layer of insulation on electric hand tools. It gives the operator of the tool an extra measure of protection in case of a short to the equipment case. If the equipment has an effective, ULL laboratory approved system of double insulation and is so marked, a third wire grounding conductor is not required.

17.9.

(1) Danger to technicians unsuspecting of reversal of color coding on the designated leads. (2) A short to ground between the switch and the load could cause the equipment to run indefinitely, regardless of the position of the switch. (3) Bulb sockets cause the threads on a light bulb to become "hot".

17.10.

An electric "arc" is the completion of an electrical circuit just prior to contact between two conductors. A "spark" is an electric "arc" occurring as an instantaneous discharge of a statically charged object.

17.11.

Class I, II, and III locations describe the type of hazardous material present: Class I--gases and vapors; Class II--ignitable dusts; Class III--ignitable fibers or flyings.

17.12.

"Group" is a classification of the material type within the class. "Division" refers to the extent of the hazard, i.e., whether the hazardous atmosphere in that location is expected to occur during normal operations or to occur occasionally, such as upon occurrence of a spill.

17.13.

A circuit tester is used to determine if a suspected circuit is energized. A continuity tester is used on de-energized circuits to determine if the circuit is complete. It can also be used to check if an object is properly grounded by checking the object's continuity with another object which is already known to be grounded.

17.14.

(1) (2) (3) (4) (5)

Improper grounding of portable tools and appliances Exposed live parts of electrical circuits Improper use of flexible cords Improperly marked disconnects Worn, frayed, or inadequate connection of plugs to cords

17.15.

Starting with the ―given‖ that the bulbs each consume 5 watts of power, whether the Christmas tree lights are connected in series or in parallel is irrelevant because the answer to the problem is the same either way. Most Christmas tree lights are connected in parallel, but for illustration, both solutions are demonstrated here. It is recognized that the RESISTANCES of the bulbs are vastly different, depending upon whether you assume that the bulbs are connected in series or in parallel. Method I: Assume a parallel circuit In a parallel circuit, each resistance sees the full voltage. If W = V x I and I = V/R, then W = V2/R or R = V2/W for each branch R = (110)2/5 = 2420 ohms 1/RT = 1/R1 + 1/R2 + 1/R3 ... etc. 1/RT = 8/2420 RT = 302.5 ohms I = V/R = 110/302.5 = 0.364 amps Method II: Assume a series circuit In a series circuit, the voltage drop is divided among the components in relation to their resistance. In this case, all are equal. 110V/8 = 13.75 volts per bulb R = V2/W = (13.75)2/5 = 37.81 ohms RT = R1 + R2 + R3... etc. RT = (37.81)8 = 302.5 ohms I = V/R = 110/302.5 = 0.364 amps Method III: Assume it doesn't matter. I = W/V = (5 x 8)/110 = 40/110 = 0.364 amps The current in the hot wire and the neutral wire are equal.

17.16.

Yes, according to Figure 17.1, 363.6 milliamperes is usually fatal.

17.17.

The worker will probably be shocked since his/her body will likely provide the ground to complete the circuit. If the worker is "moist" enough or otherwise provides good contact and the current passes through his/her chest, the mishap will probably be fatal.

17.18.

Since there usually is little or no voltage potential between the neutral wire and ground, there would be no shock. However, a considerable load (resistance) downstream from the neutral could cause a voltage to ground to occur on the neutral, possibly sufficient to be fatal.

17.19.

The ground wire, unlike the neutral, is normally not a current conductor and should always be at zero voltage to ground and thus would not be hazardous.

17.20.

Improper grounding; rough treatment of light and cord (pulling the cord, the cord being pinched by a closing hood on a car, dropping the light when the bulb burns a worker's fingers, etc.), wet hands and clothing when handling light; standing on ground (sometimes wet with dew) barefoot; leaning bare-chested over fender of car, making good contact between metal and chest.

17.21.

The ordinary circuit breaker checks for overloaded circuits (circuits carrying larger than the amperage limit set for the circuit). Typical amperage limits in household circuits are 15, 20, and 30 amperes, depending upon the rating of the circuit (a ―20 amp circuit‖ for example). The GFCI checks for imbalances between the amperage carried by the hot conductor and the amperage carried by the neutral. Any imbalance between these two implies that there is a leakage to ground somewhere in the circuit. Typical limits for which a GFCI will trip is around 0.5 amp.

17.22.

The grounding conductor (―ground‖) is at nearly same voltage potential as the neutral conductor, even in a correctly wired circuit, because both are grounded back at the meter. Therefore, a simple circuit tester is unable to detect any difference in potential between the ground and the neutral, whether they are correctly wired or incorrectly ―jumped‖ together right at the receptacle.

17.23.

Precautions should have been taken to ensure no electrical wires were beyond the wall, and if this was unavoidable, they should have been deenergized. The drill should not have been used without a proper ground wire. The worker could have been wearing insulated gloves.

17.24.

The broken ground plug removed the chance of a short circuit which would have tripped the breaker.

17.25.

There are basically two good features of electrical grounding as it is conventionally used. The first is that it is a convenient means to complete a circuit, by connecting the hot conductor to the load and the neutral to ground. The second good feature about grounding is that if the normally non-current-carrying metal parts (or other conductive parts of a machine or device) are continuously grounded, a person who contacts the equipment does not become a primary path of current flow to ground. The bad feature of the use of grounding to complete a circuit, is that connection to ground is so convenient that a person’s body can become a part of the circuit. If the person’s body is wellgrounded and the equipment is not, the person’s body can become the neutral path of the circuit back to ground.

17.26.

The grounded conductor refers to the neutral, current-carrying conductor that normally completes the circuit by connection with the load, which is in turn connected to the hot conductor. The grounding conductor refers to the safety ground that is connected to the normally non-current-carrying conductive parts of the equipment. If an accidental short occurs, the safety ground will carry the current to ground, causing the circuit breaker to trip the circuit.

17.27.

(a) The resistance of the pantleg material would likely prevent shock. If skin contact did occur, the proximity of the neutral contacts would likely prevent the passage of current through the worker's torso. Electrocution would be highly unlikely. (b)

I = V/R = 440v/10,000 = .044 amps = 44 mA

Electrical shock is likely, but electrocution is highly unlikely because of the high resistance in the circuit and the fact that the path of the current is not through the worker's torso. (c) This is a dangerous situation. A 220-volt circuit wired "hot" invites a serious shock and electrocution hazard. However in the situation described, the low resistance screwdriver shaft would likely conduct a large current and trip a breaker. The worker would also be protected by the nonconducting (wood) handle for the screwdriver. (d) This is a very dangerous situation. The worker is likely to be well-grounded via the concrete floor, especially if damp, as garages often are. The circuit is energized. The worker is foolish to believe that avoiding contact with both hot and neutral at the same time will protect him. Contact with the hot wire alone would permit a path to ground to pass through his body to the floor. Electrocution is a real possibility here.

17.28.

This is a very dangerous situation. Note carefully that although the worker is right-handed, he is holding the work in his left hand. His bare right arm is braced against a water pipe and therefore acts as an excellent connection to ground. Calculation of ground path current: I = V/R = 120v/600 = .2 amp = 200 mA The probable path is from the worker's left hand through his torso (including heart and lungs) and to ground via the right arm braced against the water pipe. The breaker will not likely be tripped. The ground path carries a current of a mere 200 mA, whereas at least 15 amp would likely be required to trip the breaker. Electrocution is a real possibility considering the factors already stated.

17.29

Fibrillation is rapid and weak pulsations of the heart due to exposure to electric shock, especially alternating current in the 50 to 60 Hz range. Once fibrillation begins it is difficult to arrest without defibrillation equipment and death is the virtually certain and almost immediate result.

17.30

The voltage is alternating, not direct. the likelihood of fibrillation.

17.31

Peak voltage

17.32

17.33

=

240v x 1.414

=

339.4 volts

Effective voltage =

80v x 0.707

=

56.6 volts

Effective voltage =

170v x 0.707

=

120 volts

Alternating current increases

=

Effective voltage x 1.414

=

Peak voltage x 0.707

=

Peak voltage x 0.707

=

60 watts/120 volts = 0.5 amp

W = VI and I = W/V Effective current Peak current flow =

Effective current x 1.414

=

.5 amp x 1.414

=

0.707 amp

17.34

A low resistance path to ground in the third wire or grounding wire of the circuit will cause an immediate current overflow in the event of a short to the equipment case or other grounded part of the equipment. This current overflow will cause the circuit breaker to trip quickly, breaking the flow of all current, including the fractional part of the circuit that might be flowing through the low-resistance grounding path; it does not protect the person being shocked by drawing the current to the ―path of least resistance.‖ The person will continue to receive current flow in accordance with Ohm’s law, until the breaker removes the voltage.

17.35

If the circuit has reversed polarity, the switch will be on the neutral, not the hot wire. Any short to ground between the load and the switch will simply complete the circuit regardless of whether the switch is on or off (closed or open). Therefore the equipment will continue to operate whether or not the switch is on or off. The short to ground through the equipment case will not trip the breaker in this case because it is the neutral that is making contact with the equipment case, not the hot. A short between the neutral and the equipment case will usually go unnoticed and the equipment will continue to operate. Contract between two parts of the hot circuit that bypasses the switch will also permit the equipment to continue to operate without regard to the status of the switch.

17.36

―Open ground‖ refers to the safety ground not being connected to a reliable source of ground. Since the safety ground does not carry current unless there is a short to the equipment case or other noncurrent-carrying parts of the equipment, no one will ever notice the fault ―open ground‖ in ordinary operation. Sloppy electrical wiring that leaves safety grounds open will not normally be noticed by anyone, unless an accident occurs.

17.37

Yes, Division 1 approved equipment is also acceptable for Division 2 locations, provided that the Class designation is compatible. Because Division 1 equipment is ―explosion-proof,‖ it is more expensive than ―vapor-tight‖ Division 2 equipment. Therefore, economics demand that Division 2 equipment will be preferred in such situations. However, it is not acceptable to use Class I approved equipment in Class II locations. The ―Class‖ designation refers to the type of exposure, not the degree of hazard. Class I is flammable liquids and gases, whereas Class II is ignitable dusts, as in grain dust, for example. The hazard mechanisms are different. Grain dust may settle in heavy layers and cause heat buildup within the equipment that may start a smoldering fire. Class I locations are not subject to the same hazards of heat buildup. Therefore, equipment that might be entirely satisfactory for exposure to Class I atmospheres could cause a fire when exposed to Class II atmospheres.

17.38.

One way to prevent this fatality was suggested in the problem statement. Also periodic inspection of electrical tools and cords is a way that the faulty condition could have been noticed and repaired before the fatal accident. The ground wire usually helps to protect the worker, but sometimes it contributes to the hazard. If the wire used to hold the chuck key to the cord had also contacted the ground wire as well as the hot wire, it would have shorted out the circuit, possibly preventing the fatality. However, in this case, ironically the ground wire contributed to the fatality. The worker was holding the electric drill in one hand and contacted the energized chuck key with the other hand. The wellgrounded case of the tool provided the path to ground which enabled the current to pass through the worker's body--hence the fatality.

17.39.

Class I, Division 1; Group is probably C, perhaps D. The class is I because of the presence of flammable vapors. Division 1 is appropriate for normal manufacturing operations in which regular exposures to hazardous concentrations would exist. Group would not be A because the ignitable agent is not acetylene. Group B is also not likely because chlorobenzene is not a gas. Group C and D both apply to flammable chemical liquids of which chlorobenzene is an example.

17.40.

This case study was intended to provide a variation on the previous case study (Case Study 17.39). The new process equipment is apparently intended to permit a re-classification of the hazardous location from Division 1 to Division 2 and would enhance safety and vastly impact the requirement for special wiring, saving considerable equipment cost. However, the problem stated that "such occurrences arise frequently out of a need to regularly clean the in-feed mechanism." Unfortunately, this frequent need to open the closed system, which permits chlorobenzene exposures, negates the advantage and would justify retaining the Division 1 rating.

RESEARCH EXERCISES 17.41.

The National Fire Protection Association (NFPA) publishes the National Electrical Code. In addition the website for NFPA (http://www.nfpa.org) has many other fire safety publications and pamphlets, not only in English, but in other languages as well (click on NFPA International). Safety publications include such topics as fire safety in the home, fire safety tips, fire protective clothing, and fire prevention and protection educational materials for children.

17.42.

The National Safety Council publication Accident Facts has tabulated annual estimates for the number of electrocutions. The figure has been continuing a downward trend in recent years. The total for 1995 (shown in the 1997 edition) was 347 and for 1996 (shown in the 1998 edition) was 279. NSC’s Injury Facts, 2002 Edition, (previously ―Accident Facts‖) reports a total of 437 deaths from exposure to electric current in 1999. This most recent edition of Injury Facts did not show a breakdown between electrocutions on- versus off-the-job.

17.43.

The NCM database can be used to check citation frequencies. Following are example citation frequencies for the top ten most frequently cited electrical standards:

Rank 1 2 3 4 5 6 7 8 9 10

Std cited 305(b)(1) 305(b)(2) 304(f)(4) 305(g)(1)(iii) 303(g)(2)(i) 305(g)(2)(iii) 303(f) 303(g)(1)(ii) 304(a)(2) 303(g)(1)(i)

Description Elect boxes: unused openings or unprotected conductors entering boxes Open electrical boxes without covers Grounding path broken or not continuous Misuse of flexible elec cords (subst for fixed wiring or run thru holes in wall) Exposed live parts Electric cord plugs: missing or inadequate pull protection (strain relief) Inadequate marking of electrical disconnects Access space around electrical equipment blocked (i.e., by other eqpmt) Reversed polarity Inadequate clearance for access around electrical equipment (for maint)

Citations 2159 1729 1430 1429 1378 1346 1158 757 455 363

The above list can be seen to approximately match the list of ―frequent violations‖ discussed in Chapter 17 of the text. The rank shifts somewhat from year to year, but the same, familiar problems continue over the years to generate the most OSHA citations. There is some variation in the way various OSHA inspectors choose to write a citation. The pattern of citation sometimes follows current OSHA inspector practices. For instance, the familiar standard covering ―exposed live parts‖ has been used by some OSHA inspectors to cite open electrical boxes as well. 17.44.

The objective of this exercise is to give students practice in using the OSHA website and the NCM database. The answer can obviously take on many forms.

CHAPTER 18

SOLUTIONS TO END-OF-CHAPTER EXERCISES

18.1.

5 foot-candles. May be dropped to 3 foot-candles for concrete placement excavation and waste areas, accessways, active storage areas, loading platforms, and refueling and maintenance areas.

18.2.

Lasers may be used as tools for checking steel girder alignment and deflection in bridges and buildings.

18.3.

Tensile strength = 4000 lbs. (1) The shock load of a fall may be several times the weight of the individual. (2) A safety factor is included in the tensile strength specification.

18.4.

A safety belt lanyard is that part of a fall protection system which attaches to the safety belt on one end and the lifeline or structure on the other. Nominal breaking strength = 5400 pounds

18.5.

A triple rolling hitch is a knot used to attach a lanyard to a lifeline.

18.6.

Hydraulic tools operate with higher pressure than pneumatic tools which causes a higher degree of hazard. Hydraulic pressure is supplied by a liquid which can have an electrical conductivity or fire hazard associated with the chosen liquid. Hydraulic tools are quieter than pneumatic tools.

18.7.

The rear of crane. The rear of the rear of the

18.8.

Helicopter hooks present an additional hazard of the hook possibly not disconnecting at the proper time. A backup mechanical disconnect is used to alleviate this hazard.

18.9.

ROPS (Rollover Protective Structures) is an OSHA-specified means of protection for the operator of a vehicle in case of a rollover of that vehicle.

18.10.

(1) Operator visibility (2) Pedestrian awareness

18.11.

A trench is an excavation in which: (1) the depth is greater than the width, (2) the width is no greater than 15 feet.

18.12.

A trench jack placed too high can be damaged as shown in Figure 18.16.

18.13.

Rebar is a rod of steel used to reinforce poured concrete structures. It can be a hazard when the end of the rebar protrudes past the last level of concrete while waiting for another layer of concrete. The protrusion can be a trip hazard, or a worker could be impaled upon it in a fall.

18.14.

When the fall distance exceeds 25 feet.

18.15.

A 1/2 inch wire rope approximately 42 inches high kept taut.

18.16.

The building to be demolished may have previous structural damage. There could be a hazard of an uncontrolled collapse of some part of the building.

18.17.

Yes, a fire that has started in an area other than the explosives compartment could be extinguished, saving a disastrous explosion.

18.18.

(from Figure 18.10) Clearance

many cranes has a swing radius that exceeds the base of the poor visibility of the crane operator plus the extended crane present a hazard of crushing personnel between the crane and some other object.

= = = = 

10 ft + (0.4 in)(550 - 50)/12 10 ft + (0.4)(500)/12 10 ft + 200/12 10 ft + 16.6 26.6 ft.

18.19.

(from Figure 18.10) Clearance = 16 ft.

18.20.

(from Figure 18.10)

Clearance = same calculation as for Problem 18.18 Clearance  26.6 ft 18.21.

(from Figure 18.10) Clearance = 4 ft.

18.22.

No; the platform is 27 feet from the ground, so the worker's safety belt would normally be at his or her waist, approximately at 30 feet (27 + 3). If the worker fell off the platform the maximum fall distance would be 30 ft - [40 ft - 12 ft] = 2 ft Such a fall distance is well within the 6 foot limit specified in standards for lanyards.

18.23.

Fall distance should be limited to 6 feet. However, the first step in this problem is to determine the lowest point at which the platform can be placed and it still remain feasible for the worker to stand on the platform while attached to the 20 foot safety line. The attachment point on the safety line would hang at an elevation of 15 feet (35 – 20 = 15). Considering various worker heights, assume that a worker’s body in a standing position would naturally reach at least another 3 feet below the point at which the lanyard is attached to the worker’s safety harness. Therefore, the working platform could be attached as low as 12 feet from the ground (15 – 3 = 12). Any lower level for the platform would leave the shorter workers hanging from their lanyards, because their feet would not reach down to the working platform level. To limit the fall distance to 6 feet, the highest level at which the platform could be placed would be 18 feet (12 + 6 = 18). Lowest level: 12 feet Highest level: 18 feet

18.24.

Mushroomed heads on chisels may release tiny metal fragments when the chisel head is struck. These metal fragments are a hazard to the eyes and other body parts.

18.25

1. 2. 3.

18.26

There are 12 power levels. The 12 levels are divided into two groups of 6 each, the group being designated by the color of the case as follows; Brass: lighter (less powerful) group Nickel: heavier (more powerful) group

Life jackets or buoyant work vests. Ring buoys every 200 feet. A lifesaving skiff whenever workers work over or near water and a danger of drowning exists.

Within the two groups there are six levels each, the levels being designated by the color of the load. The load color code sequence is as follows from lightest to heaviest: Gray, Brown, Green, Yellow, Red, Purple 18.27

Every shift

18.28

Via gravity chutes to ground level. If the height is greater than 20 feet the gravity chutes are required to be enclosed.

18.29

Flammable liquids

18.30

The hose flies about dangerously, propelled by the rapidly escaping air under pressure. Federal standards require in-line automatic shut-off valves that close whenever a line break causes a sudden depressurization in the line. The problem is that under heavy usage with large airflows, the shut-off valves may close during normal operation causing a nuisance.

18.31

The obvious way to two-block a crane is to hoist the load block too high to the point at which it contacts the boom tip. Less obvious are the ways that the geometry can be changed by moving the boon while the hoist is held fixed. When the boom is lowered, the load block will slowly creep closer to the boom point even with the hoist fixed. This is due to the positioning of the hoist drum behind the pivot point of the boom. Another way to two-block the crane is to extend a telescoping boon while the hoist is held fixed.

18.32.

The two principal hazards associated with the choice of hydraulic

fluids are fire and electrical shock through contact with high-voltage utility lines. For general hydraulic tool applications, the fire resistance characteristic of the hydraulic fluid takes priority. However, when working in construction and alteration of electric utility transmission and distribution systems, the hazard of electrical conductivity takes precedence over the fire hazard. Therefore, the hydraulic fluids used for insulated sections of derrick trucks, aerial lifts, and hydraulic tools that are used on or around energized lines and equipment for power transmission and distribution are required to be of the insulating type. 18.33.

Powder-actuated tools are similar in appearance to hand-guns and function in a similar way, except that for powder-actuated tools the projectile is separate from the cartridge. A powder-actuated tool, if used incorrectly, is fully capable of killing a person, the same as a handgun will. Powder-actuated tools may be even more dangerous, because the cartridge power must be carefully selected to be sufficiently powerful to drive the projectile, but not so powerful as to drive it completely through the wall or other surface so that it dangerously emerges from the back side, possibly killing an unsuspecting coworker. There are twelve different power levels for the cartridge (coded by color), so a decision as to which power level is to be used for a given application must be made carefully.

18.34

Due to the sensitivity of the GFCI device it can sometimes trip due to small, perhaps harmless, leaks to ground in a typical construction site outdoors. This is called "nuisance tripping" .

18.35

A cornice hook is used to secure suspension ropes for scaffolds by forming an attachment at the edge of a rook if there is a vertical barrier at the edge. Tiebacks tied to a secure point are required as a secondary means of support.

18.36

People think of concrete blocks as very rigid and durable. However, a tiny scaffold foot directs a highly concentrated load on the concrete block and can break through the concrete block, causing a critical shift aloft. Unfortunately, the timing is usually bad because the scaffold loading is usually the greatest when personnel are on the scaffold.

18.37

Stairways often consist of a steel structure with concrete poured into the treads during construction. Often the steel stairway structure is used as a stairway before the concrete treads have been poured. The unfilled pan-type treads represent a tripping hazard to personnel who use the stairs before the pans are filled. Standards require that the empty tread cavities be filled in with lumber or other material to form a temporary tread while the stairway frame is being used during construction.

18.35

The crane likely two-blocked. While the boom was lowered, the hoist was held fixed and the load block and headache ball slowly creeped up to the boom point. See diagram. The accident could have been prevented by motoring out the hoist while lowering the boom or automatically by an anti-two-block device.

Position 1.

Therefore,

Boom nearly erect.

c2 >

c1

Position 2.

Boom lowered.

a1 = a2 (fixed by crane geometry) b1 = b2 (fixed boom length) θ <  which causes the two-block.

18.39

Number of fatalities due to falls: 23 Additional falls after installing safety nets: 10 Number of fatalities due to falls after installing the safety nets: 0

18.40.

During its own construction

18.41.

―Two-blocking‖ occurs when the load hook or hook block is drawn up too close to the boom point of a crane or to the upper block in a reeving arrangement. When the lower block and the upper block (or crane boom point) make contact, any further winching of the hoist rope imparts a severe tensile stress to the wire rope. Two-blocking often results in breaking the wire rope and the fall of the load and load block. Many fatalities have resulted from two-blocking. ANSI requires ―two-blocking damage prevention features‖ on mobile hydraulic cranes if the crane is of the telescoping boom type with less than 60 feet of extended boom.

18.42.

Prior to use on each shift.

18.43.

A certain resiliency or elasticity in artificial fiber ropes lessens the shock load when arresting a fall.

18.44.

Cracking, chipping, and splintering of material from contact with tools or fasteners. The flying debris can cause eye injury.

18.45.

No splices are permitted in flexible electrical cords on construction sites unless they are properly molded or vulcanized.

18.46.

The ―headache ball‖ is a ball-shaped weight used to keep a necessary tension on a crane’s running rope (wire rope) when the crane hook is not loaded. The headache ball is smaller and lighter than a ―wrecking ball,‖ which is used for a different purpose.

18.47.

Hammerhead tower cranes have the advantage of the convenient placement of a cantilevered counterweight on the end of the jib opposite the work.

18.48.

Helicopter crane hooks must not only be reliable in holding the load without releasing it at the wrong time; they must ALSO release the load reliably at the right time. For safety, a mechanical override is required that can be used in an emergency to release the load in case the electrical release fails. (Incidentally, this is an example of the Fail-Safe Principle of Redundancy discussed in Chapter 3.)

18.49.

Material hoists and personnel hoists are different in design and safety factor. It is a violation of standards to use a material hoist for personnel; however, it is OK to use a personnel hoist to lift material provided that rated capacities are not exceeded.

18.50.

―Articulating‖ means capable of bending in the middle, whereas ―hydraulically extensible‖ means ―telescoping.‖ Vehicle-mounted boom platforms can be of either design.

18.51.

An example engineering control would be equipping the vehicle with an automatic backup alarm for warning pedestrian workers. An example administrative or work practice control would be posting an observer to warn pedestrian workers to get out of the way whenever the vehicle moves in reverse.

18.52.

―Angle of repose‖ refers to the slope of a pile of excavated earth or other material. If the angle becomes too steep, the pile will begin to slide away, depending upon the material in the pile and its condition. Angle of repose is a critical safety consideration because, if the pile begins to slip back into an excavation, it can endanger workers inside the trench or other excavation.

18.53.

1. hydrostatic pressure of wet concrete just after pouring. 2. vibrating equipment applied immediately after pouring (the most dangerous time) adds to the stress on the concrete forms.

18.54.

Earlier editions of the text listed the following as the top five causes of construction fatalities: Falls Electrocutions Vehicle rollovers Personnel runover by vehicle Excavation cave-ins Current editions do not list these causes because of the paucity of current data on the causes of construction fatalities. It is probably unfair to ask students to find conclusive answers to this question, but it is a good question for student research.

RESEARCH EXERCISES 18.55.

The National Safety Council publication Injury Facts reveals that farm hazards are very similar to construction hazards, listing such examples as transportation accidents, falls, and especially machinery hazards. Tractor fatalities from rollovers has been targeted as a very frequent cause of fatalities. The National Safety Council publication Accident Facts, the predecessor publication to Injury Facts, reported that in 1995, overturns accounted for 55% of all on-the-farm fatalities reported to the National Safety Council, with an annual rate of 5.5 deaths per 100,000 tractors. For all tractor deaths combined the estimated number of tractor deaths nationwide for the year was shown as 431 in the 1997 edition of Accident Facts. Formerly the largest source of farm fatalities, there were only 100 fatal tractor accidents in all of 2001, as reported by the National Safety Council in the 2002 Edition of Injury Facts. When all farm fatalities are counted (not just those that occur while actually on the farm), transportation ranks as the number one exposure to fatalities. The number of transportation fatalities reported for the ―agriculture, forestry, and fishing‖ industry was reported as 3744 for the period 1992-2000 (ref. Injury Facts, 2002 Ed). Averaged over the nine year period, the yearly average total would be approximately 416.

18.56.

The following is quoted from OSHA Directives - STD 3-15.3 - 29 CFR 1926.705, Requirements for Lift-Slab Construction Operations -Inspection Procedures and Guidelines: G. Background. The standard for Lift-Slab Construction Operations, 29 CFR 1926.705, was promulgated on October 18, 1990, at Federal Register, Volume 55, No. 202, pages 42306 to 42330; and all portions of the standard are effective on December 17, 1990. 1. A tragic occurrence on April 23, 1987, at Bridgeport, Connecticut, resulted in the death of 28 workers and injuries to many others. The workers were in the act of erecting a building using the lift-slab method of construction. The collapse resulted in the highest death toll from a construction-related activity in the United States since the 51 deaths in 1978 attributed to the cooling tower collapse at Willow Island, West Virginia.

18.57.

The case study states that the worker’s lifeline was attached to an attachment line that was in turn attached to the beam on which the worker was standing. Since the lanyard was attached to the worker’s body harness, the attachment at that point was considerably higher than the beam on which the worker was standing, perhaps an estimated four feet higher than the soles of his shoes. Therefore, the worker fell this estimated four feet PLUS the six-foot length of the lanyard PLUS the five-foot effective length of the looped, 10 foot attachment line. This adds up to 4+6+5 = 15 feet. At the 15-foot point in the fall, then, the lanyard would become taut, and the worker’s body would swing below the attachment point of the lanyard. This accident points to the fact that in ANY FALL the fall distance depends not only upon the length of the lanyard but also on where the worker is standing when the fall begins. In this accident it also depended upon the additional fall distance created by the 10-foot, looped attachment line.