CIH Exam Essential Practice Questions
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CIH EXAM ESSENTIAL PRACTICE, 2020
Farcas, Hammond & Cena
CIH EXAM ESSENTIAL PRACTICE SIMPLY AND THOROUGHLY EXPLAINED By Dr. Daniel Farcas, CIH, CSP, CHMM Damien Hammond, MS, CIH, CSP Dr. Lorenzo Cena, MS, PhD
2020
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Copy righ Copyri ghtt Dani Daniel el F Farcas, arcas, 2 202 020 0 www.DanielFarcas.com www.DanielFarcas.com
ISBN: 97986461858 9798646185878 78
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All s o av A avai aill abl ab l e:
CSP EXAM CSP EXAM Equ Equatio ations ns simply sim ply explained a and nd with wit h exampl example es
CIH EXAM CIH EXAM E Equ quatio ations ns simply sim ply explained a and nd with wit h exampl example es
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Dr. Daniel Farcas Farcas has more than 20 years of experience in conducting scientific research and leading production teams in a variety of fields, including public health, infection control, nanotechnology, microbiology, silica, and asbestos. He is author or co-author of numerous scientific manuscripts in peer-reviewed journals. His research interest are erionite, an emerging naturallyoccurring carcinogen that, through continued and frequent exposure can lead to mesothelioma and firefighters' exposure to Methicillinresistant Staphylococcus aureus (MRSA) through turnout gear or personal protective equipment (PPE) vectors. Dr. Daniel Farcas is a Certified Industrial Hygienist (CIH) CP #11723, a Certified Safety Professional (CSP) #36048, and a Certified Hazardous Materials Manager (CHMM) #24712.
Mr. Damien Hammond Hammond SR SR,, President of Windjammer Environmental, has over 20 years of experience in providing industrial hygiene, environmental, and occupational health and safety services. His educational accomplishments include a Bachelor of Science in Biology from the University of the District of Columbia and a Master of Science in Environmental Sciences and Public Policy from George Mason University. He has served as the President of the American Industrial Hygiene Association (Potomac Section), a professional organization with roughly one thousand members in the Washington DC metropolitan area. As President of AIHA (Potomac), Mr. Hammond was responsible for developing practices, which helped promote increased member participation within the organization. Since becoming a Board-Certified Industrial Hygienist and Cer tified tified Safety Professional, Mr. Hammond has grown Windjammer’s technical capabilities and expanded its national presence with operations in five states. Windjammer’s commitment to excellence serving clients such as the US Department of State, The US Coast Guard, DuPont Personal Protection, and many others have earned the distinction of being selected as one of the Emerging Businesses of 2017 by the US Small Business Administration.
Dr. Lorenzo Cena is Cena is an aerosol scientist and industrial hygienist with expertise in occupational and environmental health. He has extensive experience in the control and assessment of occupational hazards associated with exposures to aerosols and nanoparticles. Before joining the faculty of West Chester University, Dr. Cena has worked for five years for the Center for Disease Control and Prevention (CDC) in the National Institute for Occupational Safety and Health (NIOSH). He has published several articles on workplace exposures, particle characterization, toxicology, exposure assessment, and analytical methods, and has presented his work at national and 4
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international conferences. Dr. Cena is also the co-inventor of a personal sampler for nanoparticles.
“The CIH Exam - Essential Practice by Farcas, Hammond, and Cena is, as the name implies, an essential set of questions in Industrial Hygiene. It is well laid out in 16 sections. The questions are well introduced with a short narrative before the introduction of the pertinent equations and solution to the over 500 example problems. The book serves not only as a formidable preparation for the CIH exam but a good review of basic principles, a reference for many of the day-to-day technical issues confronting the practicing industrial hygienist and a guide for raising awareness of potential problems for which alert action is required. The authors bring a breadth of experience and insight into the issues handled in the text. They bring context to the basic principles to be highlighted by the examples of the questions and their solutions. CIH Exam - Essent Essent ial Practi ce should be a must-have text for everyone in the field.” field. ”
Michael McCawley, Ph.D., West Virginia University.
The authors would like to thank the following reviewers for their insightful comments and efforts towards towards improving this book: Michael McCa McCawley wley,, Ph.D., West Virginia University. Khachatur Sarkisian, Sarkisian , M.S., National Institute for Occupational Safety and Health
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Content Sound…………………………………………………..7 Sound…………………………………………………..7 Vibrations...…...……………………………………33 ………………33 Ergonomics……………………………………….…35 …………………………….…35 Thermal Stressors……………………………….…40 ……………………….…40 Toxicology……………..………………….…………47 Toxicology……………..………………….…………47 Personal Protective Equipment………………….83 Equipment………………….83 Biostatistics……..……………………………..…..90 ……………..…..90 Epidemiology……………………………………......98 Epidemiology……………………………………......98 Radiation………….……………………………..….100 Hazardous Materials Management…………..… Management…………..…112 112 Sampling……………………………………..…….113 ………..…….113 Immediately Dangerous Situations...................120 Biosafety...………………………………………….124 Biosafety...………………………………………….124 Ventilation……………………………………..…...133 Ventilation……………………………………..…...133 Community Exposure…………………….………144 Exposure…………………….………144 Working Environment…………………………….150 Environment…………………………….150
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Sound 1. What is sou sound? nd? Sound is vibration (physical disturbance at the molecular level) that is perceived by the human ear and redirected first mechanically and then biochemically to the brain. Sound propagates as an audible wave of pressure through a transmission medium such as a gas, liquid, or solid. Sound cannot be transmitted in a vacuum. 2. How does sound sou nd propagate? pro pagate? Sound propagates as fluctuations above and below atmospheric pressure (compressions and rarefactions), and sound’s sound’s wave energy eventually dissipates by converting to heat. Therefore, sound does not travel as far as light. Sound energy can be transferred to an object as vibration. Thus, T hus, a sound of high intensity and the right resonant frequency can shatter a glass. 3. What is noi se? se? Noise is unwanted sound that does not carry information and is the most frequent complaint of workers today. The industrial hygienists’ task is to quantify the the exposure by magnitude and duration and provide the appropriate administrative, administrative, engineering, or personal protective equipment (PPE) controls. 4. What is the speed of sound? sou nd? Sound waves are vibrations, so the wave amplitude or loudness of sound and frequency can change (like in the Doppler effect), but the speed through the medium remains constant or can also vary with changes into temperature. speed which The the sound propagates is proportional the medium’s The elasticity andatdensity. speed of sound is higher for dense materials. Sounds propagate in air at 332 m/s, in water at 1,433 m/s, in wood at 3,962 m/s and steel at 5,960 m/s. 5. How many types of sound wave waves s exist? exist? There are two types of sound waves: A. Transverse or ripples sound waves which move horizontally, the molecules move vertically (e.g., sound in water), and the energy transfer is sideways.
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B. Longitudinal or compression sound waves which move vertically, the molecules move horizontally (e.g., sound in air), and the energy of transfer is in parallel.
6.
Wha Whatt does the ave average rage sound pre pressure ssure fluc tuation in the
atmospheric environment to?(compressions) to? Because sounds are waves with peaks above the atmosphericequal pressure equal in number and opposite in amplitude to the peaks below atmospheric pressure (rarefactions), the average pressure fluctuation in atmosphere equals 0 (zero).
7. How is sound quantified? quantified? The perception of sound is a human process. Sound is visualized as a wave. The frequency alignment of sounds is known as a spectrum. The sound frequency range is divided into sets of frequencies called octave bands. The human ear perceives pure tone frequency as pitch. Language is a fast modulation of pure tone frequencies. The amplitude measures the loudness.
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8. Wha Whatt is tinni tus? tus? Tinnitus Tinnitus (ringing, whistling, or hissing in the ears) takes place in sensory auditory cells in the cochlea of the inner ear when they are damaged. Although tinnitus is heard in the ears, its source is really in the network of brain cells. Note: If an insect crawls in the ear canal of a worker pour mineral oil, olive oil or baby oil into the ear, this will suffocate and quiet the insect until a medical doctor will remove it. 9. What is the sou sound nd imp impeda edance? nce? Sound is amplified before reaching the middle ear and inner ear. This process is called impedance matching, and the incoming vibration from the comparatively large pinna (ear auricle) is focused on the small tympanic membrane and much smaller oval window. 10. At what frequency does nois e dama 10. damage ge occur s gra gradually dually a and nd painlessly without the worker being aware of it? Audiometric tests are the first sign of hearing loss. loss . Because the outer ear resonance is in the range of 4,000 Hz, the sensorineural hearing loss appears in this region. The employer should keep the audiometric test records for the length of the affected worker ’s ’s employment. employment. Note: The speed of sound in air is 1,125 ft/s, so at 4 kHz we have: λ = c/f = 1,125/4,000 0.28 feet, and 0.28 feet x 12 in/ft = 3.36 inches (about the average ear length resonant frequency). Where c is the speed of the wave, λ is the wavelength, and f is frequency.
≌
Note:: Observe the 4000 Hz “notch” or “dip.” Note “dip.” 9
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The three 11. What are the thr ee main anatomic al secti 11. sections ons of the ea ear? r? The anatomical sections are: (A) the outer ou ter ea ear r which which consists of the pinna and the ear canal, directing sound to the eardrum; (B) the middle ear which contains the eardrum, the three ossicles (small bones that transmit the eardrum’s vibrations to the inner ear, and the eustachian tube that drains fluids to the throat and helps in stabilizing ear pressure; and (C) the inner ear which contains the cochlea that converts vibration into electrical impulses transmitted to the brain by the auditory nerve. The vestibular system is also contained in the middle ear and is responsible for the organs of motion, spatial orientation, and balance. 12. What are the thr 12. three ee bon es con conduc ductin tin g soun d in the mid dle year? year? The middle ear contains the Eustachian tube and sound-conducting bones (or ossicles): malleus, incus, and stapes (MIS) or hammer, anvil, and stirrup (HAS). The stapes sends impulses to the cochlea through the oval window.
13. What is the functi 13. fun cti on of the Eustachian Eustachi an tub e? e? The The Eustachian tube or pharyngotympanic tube connects the middle ear cavity with the nasopharynx region (mouth). The Eustachian tube’s tube’s function function is to equalize the pressure in the middle ear to the atmospheric pressure and opens during swallowing and yawning.
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Note: The pharyngotympanic tube performs other functions like it aerates the middle ear system and clears mucus from the middle ear into the nasopharynx. When the Eustachian tube is blocked, we experience the sensations of popping, clicking, or ear fullness. 14. What is the cochlea’s function? The function? The cochlea, or organ of Corti, has hair-like cells that detect sound. The location of hair-like cells corresponds to the sounds' frequency we hear. When these tiny hair-like cells vibrate, they also transmit electrical impulses to the brain through the nerves. Inside the cochlea, the mechanical energy (sound waves) is converted to electrical energy (biochemical nerve pulses).
15. What is Sound Intensit 15. Intensity y Level? Level? Intensity Level (Li) or Acoustic Intensity is the power (W) carried by sound waves per unit area (m 2) in a direction perpendicular to that area and is measured as Watts per square meter (W/m2). Sound travels from the source in all directions, so we should imagine sound as an expanding sphere.
at the source W Soundnd Intens Sou Intensityity I Power Area Sphere 4πr
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There is also a reference sound intensity I o = 10-12 w/m2 that is the auditory threshold (the lowest sound level that can be heard). Example: A siren has a sound power of 4 watts. Will this siren be heard 1 Example: A kilometer (1000 meters) away? Consider π = 3.14 and Io = 10-12 W/m2.
I 4πrP 4π4π1000m 4 W 12,560,4W000m ≅3.2∗10− W/m 1000m
The siren will be heard since it is above the threshold of Io = 10-12 W/m2. We can further use
L 10log 10log 3.2∗10− L 10∗log 10− ≌ 55 dB
to calculate the sound pressure in
decibels based on intensity.
Note: Observe that the sound intensity is inversely proportional to the square of the distance. Sound Pressure Level 16. What is S 16. Soun ound d Pre Pressu ssu re Level (S (SPL PL or Lp)? Lp)? Sound (SPL or Lp) is the effective sound pressure relative to a reference value (ambient atmospheric pressure) typically 20 µPa ( . SPL is usually measured in decibels (dB) on the A-scale (dBA).
20∗10−Pa
Example: How many pascals (Pa) are required to produce a sound pressure Example: How level of 100 dBA?
P 100 dBdBA 20 ∗ log 20∗10−Pa 10020dB log 20∗10P − Pa
10 20∗10P − Pa
(next step antilog, and since 100/20 = 5)
P = 105* 20 * 10-6 Pa = 2 Pa 12
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Note: The decibel scale is used because it is quite convenient, and it ranges from 0 to 140 dB. If we express sound in Pascals (Pa), we should have to deal with numbers as small as 0.00002 Pa to as big as 200 Pa, as shown in the table below. below. Sound Pressure Pascals (Pa) (Pa) 200 63.2 20 6.3 2 0.63 0.2 0.063 0.02
Sound Pressure Decibels (dB) 140 130 120 110 100 90 80 70 60
0.0063 0.002 0.00063 0.0002 0.000063 0.00002
50 40 30 20 10 0
Note: The sound intensity level (L i) is similar to the sound pressure level (SPL or Lp). The only difference is that the sound intensity level is a vector, having both amplitude and direction. 17. What is S Sou ound nd Power Level (L w )? )? Sound Power Level (Lw) is measured as the total acoustic power emitted by a source in all directions (does not change with the environment) to a reference value that typically is 10-12 W. Example: Estimate Example: Estimate the sound power level of a siren that emits 30 watts.
30 W L 10∗log 10− W ≌ 135 dB extremel extremely loudud and painfufull if nearby
18.
The rule of thumb for thumb for combining decibel measurements from separate
noise sources that are near each other is: 13
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dB difference 0 – 1 2 – 4
Add to the higher 3 2
5 – 9 10 or higher
1 add zero
Example: Two noise sources of 90 dBA each operate together in the Example: same room. What is the noise level in the room? The dB difference between the two sources is 90dB - 90dB = 0, so we must add 3 dB to the highest source (in this case, any one of them). 90 dBA + 3 dBA = 93 dBA Note: We obtain the same result if we use the ABIH equation formula:
N L 10log 10log= 10 L 10 log 10 10 10log 10 10 10∗log2 10∗ log2 ∗log ∗log10 10∗ 10∗0.39 0.39 93 dBdBA
BeBecacaususe:e: log logxx ∗ y log logxx log logyy
dBA A can 19. An employee who works in a station with a noise level of 93 dB perform the work for how many hours according to OSHA’s OSHA ’s PEL PEL of 90 dBA and ACGIH’s ACGIH’s TLV TLV 85 dBA?
TO . ≌ CG .≌ T
5.28hours
1.27 hours
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Note: OSHA’s OSHA’s PEL PEL has the highest TWA threshold, and the ACGIH has the lowest exchange rate. Remember that dosimeters have three settings: Settings Settings
TWA TW A Threshol d
Exchange Rate Rate
OSHA PEL
90 dBA
5
OSHA HC (Hearing Conservation) Conservation) * *
85 dBA
5
ACGIH
85 dBA
3
* OSHA requires a hearing conservation (HC) program to be put into effect starting at 85 dBA for an 8-hour exposure. Also, the employees must be notified about their exposure to noise and entered the hearing conservation (HC) program. 20. What is the soun d pressure requir ed to gene 20. generate rate a level (S (SPL PL or Lp) of 12 127 7 dB? The reference sound pressure level Po = 20 µPa = 20 * 10-6
SPL P20log 127 dB 20 ∗ log 20∗10−Pa 12720dB log 20∗10P − Pa P . 10 20∗10− Pa
Pa. Using the ABIH equation sheet formula:
(next step antilog, and 127/20 = 6.35)
P = 106.35 * 20 * 10-6 Pa = 45 Pa
21. What is the threshol d of pain 21. pain at 10 1000 00 Hz in dBA if we kno w the 2 pressure level level is L p = 200 N/m ? Remember, a pascal equals a newton per square meter and Po = 20 µPa.
140 ddBABA SPL or L 20 loglog (PP) 20 loglog (0.02000002) 20log10 140
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22. What is the inc 22. increase rease in sound pressu pressure re level ((SP SPL L or L p) when doubl ing t he sound pressure (P (P))?
200 L 20 loogg (0.00002) 20log10 140 140 ddBABA L 20 loglog (0.04000002) 20log 2∗10 20∗ log2 ∗log 10 20∗ 0.37 146 146 ddBABA
Answer: Doubling the sound pressure (P) increases the sound pressure level (SPL or Lp) by 6 dB. Also, doubling sound power results results in a 3 dB increase. 23. What is the decrease in sound pressu re level ((SP 23. SPL L or L p ) when doubling the distance?
SPL SPL 20 log 1 SPL XdB20log XdB20log((2) X20log0.5 X20∗ 0.3 XdB6
Using the ABIH equation sheet formula:
Answer: Doubling the distance decreases decreases the sound pressure level (SPL or Lp) by 6 dB. 24. What is the frequency of a 5024. 50-blade blade fan, whi ch rotates a att 1 100 000 0 RPM?
f NRM
Using the ABIH equation sheet formula:
f 50∗1000 60 833.33 Hz
Note: Fans with forward-curved blades are quieter.
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What is the phy sic al pressu re created by a an n 89 89-dB -dB sou sound nd wave wave? ? Using the ABIH equation sheet formula:
SPL or L 20 lologg
− 84.945log( 25log 0 ∗ l(og 20∗10 P )PaPa P 20∗10−Pa
We do the antilog next, 10. 20∗10P −Pa
P = (20 * 10-6 Pa) * (104.45) = 0.56 Pa
26. Wha 26. Whatt is the soluti on to the follo wing noise exposure probl em? em? A A dosimeter set to OSHA’s standard shows a noise exposure equivalent of 95 % dose exposure. What is the value in dB of this exposure?
TWA16.61log 1log % 90dBA TWA 16.61log 90 dBA 16.61 log0.95 9090dBdBAA ≌ 89.63 dBdBA
Using the ABIH equation sheet formula:
27. A A worker is exposed during an 8-hour shift to 100 dBA, what wou ld b e the OSH OSHA A no noise ise dos e % %? ?
− %D TWA 16.61 log 100 90 dBA > Dose% 10 . + . + 10. 399.98% . + 10− %D 10−
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Note: The reverse calculation is easier. Let us say one of the choices is 400%.
TWA 16.61 log 400 100 90 100 dBA
Use the reverse calculation during the CIH exam. It is faster! 28. What is the transmission loss for a wall with a sound transmission coefficient of 0.00005 at 1000 Hz?
10log20,000 ≌ 43 dB TL10log. TL10log =
This means sounds above 43 dB will pass through the wall. 29. What is the percent noise dose exposure of a worker exposed to 85 dB for 3.5 hours, 90 dB for 1.5 hours, 95 dB for 2 hours, 100 dB for 1 hour? The OSHA allowable time of exposure to 85 dB is 16 hours, for 90 dB is 8 hours, for 95 dB is 4 hours, and for 100 dB is 2 hours.
%D100∗ . . %D100∗
= 140.6% (overexposure)
30. What is the frequency of a sound wave in the air (speed 244 m/s) if its wavelength is 0.5 meters?
f λλ c 2440.5 secsmec 488 488 HHzz
31. An octave has a lo lower wer frequenc frequency y of 71 710 0 Hz and an uppe upperr frequency o off 1420 kHz. What is the center frequency?
f f f f f f √ 710 ∗ 1420 ≌ 1000 HHzz
32. What is the upper cutoff frequency if the lower cutoff frequency of a third-octave band is 708 Hz?
f f √ 2 f √ 2 ∗ 708 ≌ 892 Hz 18
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33. What is the directivity index for a sound system mounted on a wall (½ spherical radiation) and for a sound system installed in the corner of a room (⅛ spherical radiation)? radiation)? Using the ABIH equation sheet formula: DI = 10 log Q DI = 10*log(2) DI = 10*log(8)
≅ ≅
3 dB
9 dB
34. An octave band band analyzer measures 80 dB at 1000 Hz. Wha Whatt would be the equivalent at the dBA, dBB, and dBC levels?
Answer: It is 80 dB for all three weighting scales because there is no difference in weighting at 1000 Hz, as you can see from the graphic above. Sound pressure levels (SPL or Lp) measured for the A, B, and C weighting scales produce for frequencies higher than 1000 Hz analogous measurements because their differences differences are insignifican insignificant. t. 35. A noise source wa was s measured using the A, B, and C-we C-weighting ighting sca scales, les, and we obtained obtained the following results: dBA = 68, dBB = 81, dBC = 90. What is the frequency range of these measurements? m easurements? 19
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Answer: The frequency range is between 10 and 900 Hz because, at these frequencies, the noise curves for scale A measurements will be the lowest, scale B measurements will be in the middle, and scale C measurements will be the highest. Note: Changing the sound frequency also changes its loudness relative to the human ear because the human ear is more sensitive to higher sound frequencies. 36.. 36
How many class classes es of noise are there? there? There are three general
classes of noise: A. The continuous noise noise is also known as broadband noise at a constant level and spectrum (like a transformer's hum) reaching the maximum at intervals of 1 second or less. The continuous noise is measured using a sound level meter set to the slow response in dBA. B. The impact noise or noise or sharp burst noise has peaks which are hard to determine (like the sounds of hammering at a forge) and occurs less frequently than once per second. Impact noise is measured using a sound level meter set to the fast response in dBA.
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C. The intermitte intermittent nt noise noise is is a mix of relatively quiet and noisy periods. The intermittent noise is measured using a sound level meter set to the slow response in dBA or intermittent response if available. 37. What causes damage to the inn er ea 37. ear? r? Continuous Continuous noise exposure usually causes damage to the inner ear while impact noise, like a sudden explosive blast (firearms), can cause damage to the middle ear. Blows to the head or fast barometric pressure changes can also cause damage to the middle ear. Note: Plasma welding reaches one of the greatest levels of noise in the occupational environment. The plasma arc welder is exposed to noise in the range of 110 to 120 dBA. 38. When sho 38. should uld we calib rate the soun d level meters? meters? Sound level meters must be calibrated before use (to ensure reliable data) and after each use (to confirm they stayed within calibration). The annual calibration of the meter is performed by verifying against a National Institute of Standards and Technology (NIST) traceable standard. Calibration checks the sound level meter ’’s frequencies s frequencies response, the weighting networks, fast and slow meter response, and the octave bands if available. Make sure you document the sound level meter traceability (unbroken chain of comparisons) that guarantees the results of measurements. m easurements. 39. What is the hearing range for hum 39. humans? ans? An An average hearing range for a human is from 20 Hz to 20,000 Hz (or 20 kHz). Sounds are considered infrasonic if their frequency is less than 20 Hz (elephants can hear infrasonic), and ultrasonic above 20kHz (rats can hear ultrasonic). Example: If the sound in air is 1100 ft/second, and the wavelengths are calculated using the relationship:
λ
(where c = speed of sound, λ =
wavelength, f = frequency). What are the wavelengths in feet that we can hear?
c 1100 ft/s λ f f 20 wavelengths/s 55 feet/wav feet/wavelelength ngth λ k cf f 20,0001100 wavelft/sengths/s0. ngths/s 0.055 feet/wavelength
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40. What are oto tox 40. toxic ic sub stanc stances? es? Ototoxic Ototoxic substances are substances that are toxic to the cochlea or auditory nerve (the 8th nerve) and/or vestibular system. Several drugs have ototoxicity as a side effect. Ototoxic drugs include antibiotics, loop diuretics, and some nonsteroidal antiinflammatory drugs. These side effects can be temporary or irreversible. Known occupational ototoxic substances are: A. B. C. D. E. F.
Carbon monoxid monoxide e (CO) Manganese (Mn) Toluene (C6H5-CH3) Styrene (C6H5CH=CH2) Xylene (C6H4(CH3)2) Lead (Pb)
41. Why is the A-weight ed scale used in sou 41. sound nd level mea measur sur eme ements nts ? The A-weighted scale, abbreviated dB(A) or dBA, is used in sound level measurements because it is related to the response of the human ear and is correlating to the injurious effects of the noise exposure to the worker’s ear. worker’s ear. 42. What frequenci es an Octave Band Analyze 42. Analyzerr has? has? Octave Band Analyzers commonly have the following geometric-mean frequencies: frequencies: 31.5, 63, 125, 250, 500, 1000, 2000, 4000, 8000, and 16000 Hz. 43. What are the th e center frequencies? The frequencies? The frequency bands on an octave band analyzer are conveyed as center frequencies. An Octave Band Analyzer filter set has the following geometric-mean frequencies: 31.5, 63, 125, 250, 500, 1000, 2000, 4000, 8000, and 16000 Hz. Center Ce nter frequenci es, Hz 31.5 63 125 250 500 1000 2000 4000 8000
Lim it of bands bands,, Hz 22-45 45-89 89-177 177-353 353-707 707-1414 1414-2828 2828-5657 5657-11314
1600
11314-22627 22
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44. What are the center frequenci es mos t clo sely cor 44. correlated related wit with h The sound center frequencies of the octave bands that are human s pee peech? ch? The most closely correlated with human speech and hearing are 500 500,, 1000 1000,, 2000, 2000, and 4000 Hz. 4000 Hz.
45. Which industries are not covered by the OSHA’s Hearing Industries that are not covered by the OSHA’s Conservation Conserva tion Amendme Amendment? nt? Industries Hearing Conservation Amendment (HCA) are agriculture, gas well drilling, and construction. 46.. 46
Three ways to absorb noise in industry: How is noi se absor absorbed? bed? Three
A. Porous-fibers insulation that vibrates and changes sound energy into heat (especially suitable for high frequencies, asbestos was used to absorb noise due to its fibers). B. Diaphragmatic membrane (a very thin piece of material like the tympanic membrane) that when is hit by sound waves causing vibration, absorbs the sound waves (especially useful for low frequencies). C. Resonant-air pockets material that also convert energy to heat when it vibrates. 23
CIH EXAM ESSENTIAL PRACTICE, 2020
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47. Which waves are very dir ection al? 47. al? High-frequency High-frequency waves are very directional, like a beam of light, but low-frequency waves become more omnidirectional, meaning that they radiate sound in all directions equally. 48. Wha 48. Whatt is the sound a absorp bsorp tion coe coeffici ffici ent? ent? A sound absorption coefficient of 0.6 for example means that 40% of the sound energy will be reflected, and 60% will be absorbed. If a barrier has a sound absorption coefficient of 0.99 means that 99% of the sound energy will be absorbed, and 1% reflected. Concrete reflects 99% of the noise. 49. Wha 49. Whatt is the hierarchy hierarchy of sound contro ls? The substitution of noisy equipment with quiet ones should always be the most effective control option. Engineering controls should be used before administrative controls, and personal protective equipment (PPE) should be the last resort. In a noisy workplace, try to reduce the reverberating sound by installing carpets and curtains on the ceiling and walls. This can minimize the amount of sound energy reflected through the room. 50. Do helmets pro 50. provid vid e hea hearing ring pro tection? tection? Helmets Helmets can provide sound attenuation and may be used as personal protective equipment (PPE) for bone-conducted (conduction (conduction of sound to the inner ear) sounds. 51. How much prot ection do ea 51. earplug rplug s provi de? de? Earplugs Earplugs are tested by the manufacturer and receive a Noise Reduction Rating (NRR). Since our body and bones also conduct noise waves, it is not possible for earplugs to completely block sound. To estimate the exposure with earplugs, a simple rule of thumbs can be used: Exposure = Lp-(NRR-7)/2. For environmental exposures above earplugs are no longer sufficient, and earmuffs should be105 worndB, in addition to alone the earplugs. 52. What is the actual exposu re of a wor 52. worker ker usi ng e earplug arplug s wit h NN NNR R of 26 in an environment with a machine producing a sound pressure level of 92 dB? Exposure = 92dB-(26-7)/2 = 82.5 dB dB 53. What is a Rinne test? Audiologists perform a hearing Rinne test by 53. placing a 512 Hz vibrating tuning fork on the mastoid (which conduct noise to the internal ear bypassing the middle ear, this bone is directly behind the ear) and afterfork theispatient the from audiologist know canal that he or the shepatient can hear it, the vibrating placedlet 1 cm the auditory and must 24
CIH EXAM ESSENTIAL PRACTICE, 2020
Farcas, Hammond & Cena
indicate if they can still hear it. This test quickly screens for the presence of conductive hearing loss.
54. What is a Te 54. Tempo mporary rary Threshold Shift? Temporary Threshold Shift (TTS) is a temporary shift in the auditory threshold due to high noise in the workplace and occurs in the first hours of exposure. TTS takes place through structural changes in the organ of Corti after the hair cells become fatigued. TTS is reversible up iftothe 16hair hours, Threshold Shift (PTS) cellsafter die. that, it may become Permanent 55. What are the upp 55. upper er and low lower er cut off offs s for 20 2000 00 Hz frequency ? It is easy to multiply the center frequency with 1.414 for upper cutoff and multiply the center frequency with 0.707 for the lower cutoff. 2000 Hz*1.414 = 2828 Hz (upper cutoff) 2000 Hz*0.707 = 1414 Hz (lower ( lower cutoff) Note: The same result we get if we used the ABIH equation sheet formula:
f f f f f f √ 2828 ∗ 1404 1999.69 ≌ 2000 Hz
56. What is Sound P 56. Pressur ressur e Level ((SP SPL L or Lp) 20 feet fro from m a speaker on a podi um in a reverberant room i f at 5 feet from th e sou source rce the SP SPL L is 100 100 dBA? dBA? Answer: Still 100 dBA because the field is reverberant, and the sound pressure level remains constant with distance from the speaker due to reflected sound waves. In a free field, the answer will be 88 dB because you lose 6 dB every time the distance doubles. 25
CIH EXAM ESSENTIAL PRACTICE, 2020
Farcas, Hammond & Cena
SPL SPL 20log 20log SPL 100 dB 20 ∗ log (205 ftft) ≌ 88
Using ABIH equation sheet formula for free field:
57. Wha 57. Whatt is the directivi ty index for a sound system mounted on a wall (½ spherical radiation) and for a sound system installed in the corner of a room (⅛ spherical radiation)? radiation)? The directivity index is the most common method for quantifying the directionality of noise coming from a source. Source Sourc e Ge Geometr ometry y
Directiv ity Facto Factorr (Q (Q))
Directiv ity it y Index (D. (D.I) I)
Sphere
1
10 log (1) = 0
½ Sphere
2
10 log (2) = 3
¼ Sphere
4
10 log (4) = 6
Sphere
8
10 log (8) = 9
⅛
DI = 10*log(2) = 3 dB DI = 10*log(8) = 9 dB 58. De 58. Determin termin e the total sound pressu pressure re levels on the A-scale resulting from the foll owing rea readings dings : 80 dB, 8 85 5 dB, a and nd 90 dB.
N Using the ABIH equation sheet formula: L 10log 10log((∑= 10 ) N L 10log 10log= (10 10 10) 91.5 dB 59.. 59
What are the main noi noise se categori categories es used in ind ust rial hyg iene?
The name of the colors come from visible light when a similar spectral distribution is applied: 26
CIH EXAM ESSENTIAL PRACTICE, 2020
Farcas, Hammond & Cena
A. White noise combines noise combines sounds of all different frequencies and has in each octave band twice the frequency bandwidth as the preceding octave, and so increases 3 dB per octave in power and can mask other sounds. B. carries an equal energy per octave, this means 3 dB drop Pink noi se se carries per octave but still maintains the same amount of energy per octave. Pink noise is used to treat hyperacusis (increased sensitivity to normal environmental sounds) or to mask tinnitus. C. Red noise (synonym noise (synonym for Brownian noise) has a power density which decreases by 6 dB per octave with increasing frequency. Note: Sound waves, like any other wave, transport energy. The amount of energy in a wave is proportional to the square of the amplitude of the wave (we need to square, otherwise the average will be zero, like in question 6).
60. Ca 60. Calcu lcu late the equivalent time-we time-weigh igh ted avera average ge for a noi se dos e of 99%. Using the ABIH equation sheet formula:
27
%D 100
T WA16.61log 90dBA TWA16.61log
CIH EXAM ESSENTIAL PRACTICE, 2020
Farcas, Hammond & Cena
CIH EXAM ESSENTIAL PRACTICE SIMPLY AND THOROUGHLY EXPLAINED Is available on o n AMAZO AMAZON: N: https://www.amazon.com/dp/B0892HRS4H
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