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SAFETY IS THE PREVAILING DIRECTIVE (IEEE 1100-2005,3.1.5)
Dedication To Dad and Mom and Lynda and Lindsey. For your Guidance, Influence, Inspiration and Memories. Rich K., August 2006
But to him who's scientific There is nothing more te"ijic In the falling ofthe flight ofthunderbolts; Yes, in spite ofall my meekness IfI have a little weakness It's a passion for a flight ofthunderbolts. -
GILBERT AND SULLIVAN, The Mikado
I "Lightning Protection for Engineers" was revised and updated in May 2007 I
INTRODUCTION by Josephine Covino, PhD Chairperson, Lightning Protection Review Committee Department ofDefense Explosives Safety Board http://www.hqda.army.mil/ddesb/esb.html Washington DC In 1926 lightning visited the Naval Ammunition Depot at Lake Denmark NJ. The incident virtually destroyed the Depot and caused heavy damage to nearby Picatinny Arsenal and surrounding communities. Twenty one people were killed and fifty one others injured. Damage to the Navy area alone was $46 million in 1926 dollars. The problem of lightning safety is not unique to the USA. In June 1998 lightning destroyed a large Russian Army munitions depot in the Ural mountains, near the village of Losiniy 30 kIn northeast of Yekaterinburg. At least 14 army personnel including the base commander were killed and 1300 villagers were evacuated from the area. Sources report that 240 tons ofstores were destroyed. In 2002 at a railyard in Beira, Mozambique lightning insulted a military explosives depot with considerable damage and injuries. As an outgrowth of the Lake Denmark event, in 1928 Congress established the Department of Defense Explosives Safety Board (DDESB). 'Since then we have collected 55 verifIable lightning-caused accidents in our database. The lightning safety compliance regulation DDESB 6055.9 is mandatory for military explosives installations. While DDESB takes the lightning issue seriously, for the most part this is not the case with the commercial and industrial workplace. In Denver in 1996, a refrigerated warehouse was struck by lightning and the loss was $55 million. Recent substantiated data from the National Lightning Safety Institute places annual USA lightning costs and losses at about $4-5 billion per year. The general public too does not fully appreciate lightning's hazards. Boaters, golfers, school children and people from most other walks oflife too often are victims of lightning. Education and attention to detail are the keys to lightning safety. Lightning Protection For Engineers makes a valuable contribution to the literature for such groups as specifying architects and engineers, those Authorities Having Jurisdiction, educators, libraries and interested local, state, and federal officials. We all need to improve our understanding of lightning safety issues.
•• •• •• •• •• •• •• •• •• •• •• •• t t
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A FEW WORDS ABOUT THE USE OF THIS BOOK. Lightning protection in an absolute sense is impossible because of the arbitrary, capricious, and stochastic nature of lightning strikes. Some twenty five million of them striking in the USA annually each have unique characteristics. The protection approach is highly site-specific, with many designs unique to individual facilities and structures. Mitigation of lightning insults is attempted through the deployment of a combination of exterior and interior defenses. The purpose of this Workbook is to describe and illustrate those defensive systems as they are applied in various situations. When employed in combination, the following sub-systems represent a layered defensive strategy, commonly called a Lightning Protection System (LPS). Air Terminals - an exterior defense. Lightning usually terminates on grounded objects sticking up in the air. Franklin rods are air terminals. Overhead steel cables and metal masts are air terminals. Steel towers are air terminals. Trees are air terminals. In the absence of taller objects, fences and blades of grass are air terminals. Old Ben's design developed in 1752 carried lightning from rods in the air via conductors to rods in the ground. This rod-configuration on buildings was and is based upon the Path of Least Resistance laws of physics. Nowadays, some vendors are promoting unconventional air terminal designs (ESE/DAS/CTS) seeking to gain advantage over competitors. Caveat Emptor. Of course, should lightning strike across the street from a protected facility center and couple into sensitive electronics via underground wiring, then no air terminals design of any classification has performed its role in protection. Grounding -an exterior defense. Low impedance and resistance grounding provides an efficient destination for the Lightning Beast. If site soils are composed of sand or rock they are resistive, not conductive. If surrounding soils are clays or dirt, they may be conductive. "Good Grounds" are achieved with properly configured volumetric efficiencies. We recommend buried bare 4/0 copper wire - the so called ring electrode or ring ground. Cadwelding© security fences, tower legs, and other adjacent metallics to the buried ring will augment the earth electrode sub-system. NEC 250 describes other grounding designs such as rods, plates, water pipes (beware plastic pipes underground), metal frame of bUildings, and concrete-encased electrodes. Choose your grounding design based upon localized conditions and the amount of available real estate at your location. NEC 250.56 suggests a target earth resistivity number of 25 ohms. Lower is better. Bonding - an interior defense. Without proper bonding, all other elements of the LPS are useless. Bonding of all facility incoming metallic penetrations - cables, conduits, pipes and wires - assures all of them are at equal potential. There are many interior "grounds" in modern buildings, such as computer grounds, AC power grounds,
lightning grounds, single point grounds, and multi-point grounds. All must be bonded so as to achieve the same potential. When lightning strikes, all grounded equipment must rise and fall equipotentially. This will eliminate the differential voltages in separate sensitive signal and data systems. Bonding serves to connect all conductors to the same "Mother Earth." Not convinced bonding is important? Check out NEC 250.90 through 250.106 for more details. Surge Suppression - an interior defense. Surge suppression devices (SPDs) all function either by absorbing the transient as heat or crowbaring the transient to ground (or some combination thereof). SPDs should be installed at main panel entries, critical branch or secondary panels, and plug-in outlets where low voltage transformers convert AC power to DC current and voltage. SPDs also ~hould be installed at signal and data line facility entry points and at electronic equipment. Telephone punch blocks should be Spo-protected. Beware the junk SPDs which proliferate the marketplace. Beware counterfeit or false UL and IEEE labeling. Beware of the "it sounds to good to be true" marketing hype employed by vendors. Insist on Certified Test Results to substantiate performance claims by manufacturers. Consider SPDs which have capabilities to remotely signal their operational performance. SPDs rank right behind Bonding in the hierarchy of important steps to mitigate the lightning hazard. Codes and Standards. There are excellent codes and standards, helpful codes and standards and superficial codes and standards. No one such document by itself provides comprehensive guidance for the lightning protection engineer. Familiarity with, many recognized codes and standards is vital for competency in lightning problem-solving.
NlSI Note about Sources: Some of this Workbook is original material and some is reproduced from other sources. Thanks to organizations such as Bellcore, IEEE, Erico, Dehn, MTL, IEC, NFPA, Polyphaser, lPC, MCG, Phoenix Contact, CITEl, APC, Telebyte, IEC, API, ICAE, NOAA, Vaisala, NASA, NCHRP, STC, Motorola, FAA, DOD, DOE, FAA, USGA, IClP, ILDC, ERA and others. Thanks also to individual friends worldwide in academia, business, government, industry, and the private sector.
•• •• •• •• •• •• •• •• •• •• •• •• •• •• •• •• •• • t
•• •• •• I
TABLE OF CONTENTS
1. Lightning Physics, Lightning Behavior And Lightning Safety Overview
1-22
2. Risk Assessment
23-40
3. The Grounding and Bonding Imperative
41-76
4. Exterior Lightning Protection for Structures
77-94
5. Interior Lightning Protection for the Electrical System of a Complex Facility
95-114
6. Communications Facilities, Exterior Lightning Protection
115-128
7. Communications Facilities, Interior Lightning Protection
129-150
8. Lightning Protection for High Risk Installations Containing Sensitive Electronics, Explosives, Munitions or Volatile Fuels
151-170
9. International View of Unconventional Air Terminals such as "ESE" and "DAS/CTS"
171-194
10. Lightning Safety for Outdoor Activities
195-214
11. References, Resources, Codes & Index
215-249
1
INTENSIVE WORKSHOP, LIGHTNING PROTECTION FOR ENGINEERS
Chapter One
LIGHTNING PHYSICS, LIGHTNING BEHAVIOR AND LIGHTNING SAFETY OVERVIEW
Early Creeks beli~ed that lightning W3S the weapon of 'Zeus.
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4 4 Chapter One Overview Lightning is arbitrary~ capricious~ rando~ stochastic and unpredictable. Science does not fully understand its phenomenology. However, investigations from today~ s researchers is considerable. While lightning creates major upsets and significant dollar losses to the economy~ safety from its effects is rarely employed proactively. Absolute protection is impossible but deployment of a holistic~ systematic approach can mitigate the hazards. gene~
many errors and misunderstandings dominate lightning protection efforts. "Lightning never strikes twice" is not correct. "Lightning rods provide safety for people" is not correct. New information slowly is altering the 19th Centmy Conventional Wisdom. In
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THUNDERSTORM CONVECTION PROCESS PRODUCES LIGHTNING Simplified Version: The Sun evaporates surface moisture, transforming it into clouds/gas/water vapor. Hot air causes clouds to rise over time. At about -15 C degrees, gas is transformed into solids/ice/hygrometeoriteslgraupuls. High winds (160 kmlhr) tumble the solids, with the collision process/.friction creating static electricity.
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TYPICAL WAVEFORM OF LIGHTNING
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TQ: TIme for attaining peak,current (rest value)
T1: Time for a«ainiDg 10% peak C\llTmt T2: Time for attaining 30% peak current
T3: TIme for attaining 90% peak current
rB: Time to drop to 50% of peak current (after readdng peak value)
Current
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"COLD' LIGHTNING IS A LIGHTNING FLASH WHOSE MAIN RETURN STROKE IS OF INTENSE CURRENT BUT OF SHORT DURATION. "HOT' LIGHTNING INVOLVES LESSER CURRENTS BUT LONGER DURATION. HOT LIGHTNING IS MORE 'APT TO START FIRES. COLD LIGHTNING GENERALLY HAS MECHANICAL AND/OR EXPLOSIVE EFFECTS.
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LIGHTNING LOGNORMAL DISTRIBUTION
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1% STROKES EXCEED 200,000 A 10% STROKES EXCEED 80,000 A
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50% STROKES EXCEED 28,000 A . .90 % STROKES EXCEED 8,000 A ' 99 % STROKES EXCEED 3000 A
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7
9
SEQUENCE OF STEPS IN TYPICAL CLOUD TO GROUND LIGHTNING FLASH (from Uman, The Lightning Discharge)
P Cloud Charge Distribution
Preliminary Breakdown
Stepped Leader
1.00 ms
1.10 ms
1.15 ms
1.20 ms
20.10ms
20.15 ms
~ 20.20ms
~~~~~~ t= 0
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60.00ms
National Lightning safely Institute 891 N. Hoover Ave louisville CO 80027
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62.00ms
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BEHAVIOR OF LIGHTNING - PART ONE As downward Leaders approach earth they may induce electrical and magnetic signatures upon grounded objects. Grounded objects may respond in stages: 1) accelerated electron behavior; 2) corona emissions; 3) launch of upward Streamers. When Leaders and Streamers connect, a preferential path to ground is established. Below are conditions for the Final Jump.
Downward Leader
v=
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x x
x Y = 0
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Upward Streamer
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x x x x x x x x
Upward
x
Streamer
x
x
x x x x
10
BEHAVIOR OF LIGHTNING - PART TWO Leaders close to the ground enter a "Cone of Discrimination" where they may choose to strike one or more ground targets. Striking Distance is a function of Peak Current (below). Horvath (1969, 1971) concluded that ground corona current increases in response to elevated electric fields. A "glow-to-arc" transition from point discharge (corona) to upward Streamer stage can occur at about 10 to 50 mAo Peak Current is the determining agency.
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C\J1lJ\ElIT, 1 5 kA). Assuming a five-year DE average of 75% (considered by GAl to be a reasonable estimate) gives a corrected facility flash-density range of < 0.33 to < 0.67. The median value of 0.5 flashes/km 2/yr was used for our probability calculations. Two points regarding this value of ground-flash density should be kept In mind. It Is based upon only five years (1990-95) of actual NLDN data-the network was quite new at the time this study was carried out. Analysis of data collected since that time probably would indicate a different value, although It seems doubtful that it would differ by very much. Significantly different values of ground-flash density are found in other parts of the country. However, even locations relatively dose to the area studied could have notably different values because of variations In topography. That Is one of the benefits of NLDN data, the ability to Identify differences between wide-area flash-density estimates, and site-speclflc values.
Return-Stroke Peak-Current Amplitude Over a number of decades, researchers have measured and recorded a variety of lightning parameters, with much of the data resulting from strikes to tall, instrumented steel towers. Along with current rate of rise and total charge transfer, peak return-stroke current Is considered to be one of lightning's most significant threat parameters. For the generally accepted frequency distribution of peak currents for negative lightning, the first-percentile value, 200 leA (I.e., 990/0 of all lightning Is of lower amplitude), Is generally considered to constitute a severe negative stroke. Although the NLDN detection efficiency Is less than 100%, GAl reports that it Is low-peak-current (i.e., < 5 leA) events that are missed, Thus, had all flashes been detected, the distribution of peak-current amplitudes would be expected to show a somewhat lower average value.
Facility Lightning Attractive Area
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27
Since the twelve 32-meter-tall perimeter light poles for our study appeared to be likely lightning strike points-at least for large-amplitude flashes-they were used In calculating the facility's lightning-attractive area. For the sake of simplicity, structure height was not included in our equation. It is reasonable to expect that some low-amplitude strokes will bypass the poles and attach to the structure.
As previously discussed, attractive area must take into account the peak amplitude of return-stroke current. Thus, an attractive area must be calculated for each current amplitude. The following method for dealing with the distribution of return-stroke currents Is attributed to the late J. Stahmann of Boeing/Kennedy Space center (Ref. 3). Stahmann assigned return-stroke peak currents from a large body of available data to declles-i.e., 10% of the total number of flashes being considered were placed Into each of ten bins. The mean peak current per decile was then calculated.
Facility Strike Probability Stahmann's mean peak-current per decile values were used to find the per-decile attractive area. The effect of the tall light poles on attractive area CAe) can be seen In Table 1. Although the surface area encompassed by the poles is 45*103 m 2, the lightning-attractive area is 77*103 m 2 for a 6-kA stroke and 171*103 m 2 for a 112-kA stroke. The product of attractive area times ground-flash density prOVided per-decile probability, the sum of which gave a cumulative probability. The reciprocal of cumulative probability is the mean return period (average strike frequency). Our study determined that some point of the facility will be struck by lightning-of some amplitude-approximately once every 17 years.
Table 1. Cumulative Probability of Strike to Fadllty
Jpk
D.
r
AA
(leA)
(m)
(m)
(m 2)
1
6
33
33
76,764
3.8E-03
2
13
S3
48
93,489
4.7E-03
Decile
Po
..
.18
..65
56
101,496
s.1E-03
4
23
76
62
108,624
5.4E-03
5
28
88
68
115,399
s.8E-03
6
35
101
74
122,391
6.1E-03 :
7
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45
118
81
130,658
R
(yr/fI)
#
3.
Pc
6.5E-03
28
S
57
138
89
140,196 7.0E-03
9
77
168
99
153,061
112
215
113
171,380 8.6E-03
I 7.6E-03
f
f 10
6E·02
17
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t Area enclosed by light poles: I = 312 m, w h == height of poles above ground level Ipk
r
=144 m (I x w = 44,928)
= 32
= average peak return-stroke current per decile
Os == lightning striking distance
=10 x Ipko. 65
Fg = ground flash density
-m
«
-leA
~
-m
=radius of light pole's attractive area = (2 x Os x h - h2)o.5
M == attractive area/decile = (I
t t
-m
+ 2r) x (w + 2r) - 10 x [(4 • ")/4] x r2
=0.5 {using GAl flash density analvsls}
=cumulative probability =I
t
PO
R == mea,n return period (i.e., average strike frequency)
= 1/PC
- 'years/flash
Conclusion Reasonable strike probability estimates can be made using site-spedflc, ground-flash density values that are based upon actual lightning data. Strike estimates are Interesting, and although their results provide an Indication of lightning strike return frequency, they should not be considered as absolutes. Perhaps their most useful funetlon Is to permit determination of the relative effects of changes made to a facility. Examples of such changes are: increased lightning-attractive area-either by extending the fadlity's surface dimensions and/or height (adding a vent stack or tower); plating an Identical fadllty In a location having a significantly different ground-flash density.
References 1. Golde, R.H., "Proteetlon of Structures Against Lightning," Proceedings of the Institute of Electrical Engineers, Vol. 115, No. 10, pp. 1523-1529, 1968. 2. Golde, R.H., "The Ughtning Conductor," In Golde, Lightning, Vol. 2, p. 560, Academic Press, london, 1977 (the striking distance equation attributed to E.R. love). 3. Stahmann, J.R., "Launch Pad Lightning Protection Enhancement by Induced Streamers," Boeing Aerospace Operations, Kennedy Space Center, Rorlda, september 1968.
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PO == strike probabiJity/dedle == AA x (0.1 x Fg) x 10-6 PC
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29
ANALYSIS OF NEED FOR PROTECTION With permission ftom Singapore Standards and Productivity Board Reproduced from Singapore Standmd CP33: 1996 Lightning Protection
2.1
GENERAL
Before proceeding with the detailed design of a lightning protection system, the following essential steps should be taken :
2.2
(a)
It should be decided whether or not the structure needs protection and, if it does what the special requirements are (see Clause 2.2 and Section 3).
(b)
A close liaison should be ensured between the architect, the builder, the lightning protection system engineer and the appropriate authorities.
(c)
The procedures for testing, commissioning and future maintenance should be agreed.
NEED FOR PROTECTION
2.2.1 General. Structures with inherent explosive risks, e.g. explosives factories, stores and dumps and fuel tanks usuaJly need the highest possible class of lightning protection system and recommendations for protecting such structures are given In Section 5.
For all other structures, the standard of protection recommended in the remainder of this Code is applicable and the only question remaining is whether protection is necessary or not. In many cases, the need for protection may be self--evident. for example: (a)
Where large numbers of people congregate;
(b)
Where essential public services are concerned;
. (c)
·Where the area Is one In which lightning Is prevalent;
(d)
.Wh~ there are very tall or isolated·Structures;·
(e)
Where there are structures of historic or cultural importance;
(f)
Where there are structures containing explosive or flammable
~ntents.
However, there are many cases for which it is not so easy to make a decision. In these areas, reference should be made to 2.2.2 to 2.2.8 where the various factors affecting the risk of being struck and the consequential effects of a strike are discussed. However, some factors cannot be asseSSed ·and ·these may override all other considerations. For example, a desire that there should be no avoidable risk to life or that the occupants of a bUilding should always feet safe may decide the question in favour of protection, even though it would normally be accepted that there was no need. No gUidance can be given in such matters but an assessment can. _ be made taking account of the-exposure risk· (that is. the· risk of the structure being· struck) and the following factors: (a)
Use to which the structure is put;
(b)
Nature of its construction;
31
CP33: 1996
2.2.3 Risks Associated With Everyday Uving. To help in viewing the risk from lightning in the context of the risks associated with everyday IMng, .Table 2.1 gives some figures based on 5S 6651 : 1992. The risk of death or injury due to accidents is a condition of lMng and many human activities imply a judgement that the benefits outweigh the related risks. Table 2.1 is intended simply to give an appreciation of the scale of risk associated with different activities. Generally, risks greater than 10.3 (1 in 1000) per year are considered unacceptable. With risks of 10'" (1 in 10000) per year, it will be normal for public money to be spent to try to eliminate the causes or mitigate the effects. Risks less than 10.5 (1 in 100 000) are generally considered acceptable, although public money may still be spent on educational campaign designed to reduce those risks Which are regarded as avoidable. 2.2.4 Suggested Acceptable Risk. On the basis of Subclause 2.2.3, the acceptable risk figure has been taken as 10-5 per year,.l.e. 1 In 100 000 per year.
.
"
Table 2.1. Comparative probability of death for an individual per exposure (order of magnitude only)
Activity
Risk 1 in 400
year of
(2.5 x 10-3)
Smoking (10 cigarettes per day)
1 in 2000
(5 x 10"')
All accidents
1 in 8000
(1.3 x 10' 4)
Traffic accidents
1 in 20 000
(5 x 10~
Leukaemia from natural causes
1 In 30000
(3.3 x 1005)
Work in industry, drowning
1 in 100 000
(1 x 10'
Poisoning
1 in 500 000
(2 x 10~
Natural disasters
1 in 1 000 000
(1 x 10-,
Rock climbing for 90 s..,- d~ng 50 mites by road*
1 in 2 000 000
7 )
(5 X 10.
Being struck by lightning
* These risks are conventionally expressed In this form rather than In terms of exposure for a year. NOTE. The source 01 this table Is as 6651 : 1992
2.2.5 Overall Assessment Of Risk. Having established the value of P, the probable number of strikes to the structure per year (see Subclause 2.2.2), the next step is to apply the weighting factors'. as given in Tables 2.2 to 2.6. This Is done by multiplying P by the appropriate factors to determine " whether the result, the overan risk factor, exceeds the acceptable risk of Po = 10-5 per year. 2.2.6 Weighting Factors. In Tables 2.2 to 2.6, the weighting factor values are given under the headings A to E"and denote a relative degree of importance or risk in each case. Tables 2.2 to 2.6 are mostly self-explanatory.
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30
CP33: 1996
(c)
Value of its contents or consequential effects;
(d)
The location of the structure;
(e)
The height of the structure (in the case of the composite structures, the overall height).
2.2.2 Estimation Of Exposure Risk. The probable number of srikes to the structure per year is the product of the 'lightning flash density' and the 'effective collection area' of the structure. The lightning flash density, Ng is the number of flashes to ground per km2 per year. Values of Ng vary from place to place. in Singapore the best estimate for the average annual density can be taken to be 12.6 flashes to ground per km2 per year. The effective collection area of a structure is the area of the plan of the structure extended in all directions to take account of its height. The edge of the effective collection area is displaced from the edge of the structure by an amount equal to the height of the structure at that point. Hence. for a simple rectangular bullding of length L, width Wand height H On m), the collection area has length (L + 2 H) m and width (W + 2H)m with four rounded corners formed by quarter circles of radius H (in m). This gives a collection area, Ac frn m', of: .
Ac == LW + 2LH + 2WH + .~ The probable number of strikes to the structure per year, P, is as follows:
It should first be decided whether this risk P is acceptable or whether some measure of protection is thought necessary. This is shown in Figure 2.1.
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CP33: 1996
Table 2.4 gives the weighting factor for contents or consequential effects. The effect of the value of the contents of a structure Is clear, the term 'consequential effects' Is Intended to cover not only material risks to goods and property but also such aspects as the disruption of essential services of all kinds, particularly In hospitals. The risk to life Is generally very small but, If a bUilding is struck, fire or panic can naturally result. All possible steps should therefore be taken to reduce these effects, especially among children, the old and the sick. For multiple use buRdlngs, the value of weighting factor A applicable to the most severe use should be used.
Table 2.2. Weighting factor A (use of structure)
Use to which str.ucture Is put
Value of factor A
Houses and other buirdlngs of comparable size
0.3
Houses and other buildings of comparable size with outside aerial
0.7
Factories, workshops and laboratories
1.0
Office blocks, hotels. blocks of flats and other residential buildings other than those InclUded below
1.2
Places of assembly, e.g., churches, halls, theatres, museums. eXhibitions, department stores, post offices, stations. airports, and stadium structures
1.3
Schools, hospitals, children's and other homes
1.7
Table 2.3 Weighting factor B (type of co~stru~ion)
Type of construction
Value of factor B
Reinforced concrete or steel frame with metallic roof
0.4
Membrane structure with metallic frames
0.8
Reinforced concrete or steel frame with non-metallic roof
1.0
Timber or masonry with non-metallic roof
1.4
Timber or masonry with metallic roof
1.7
Any building with a thatched roof
2.0
NOTE. A structure of exposed metal which is electrically continuous down to ground level is excluded from the table as it requires no lightning proteCtion, beyond adequate earthing arrangements.
33
CP33: 1996
Table 2.4 Weighting factor C (contents or consequential effects)
Contents or consequential effects
Value of factor C
Ordinary domestic or office buildings, factories and workshops not containing valuable or specially susceptible contents
0.3
Industrial and agricultural bundings with specially susceptible* contents
0.8
Power stations, gas Installations, telephone exchange, radio stations
1.0
Key Industrial plants, ancient monuments and historic buildings, museums, art galleries or other buildings with specially valuable contents
1.3
Schools, hospitals. children's and other homes, places of assembly
1.7
* This means specially valuable plant or materials vulnerable to fire or the result of fire.
Table 2.5 Weighting factor 0 (degree of isolation)
Degree of isolation
Value of factor 0
Structure located in a large area of structures or trees of the same or greater height, e.g. in a large town or forest
0.4
Structure located in an area with few other structures or trees of similar height
1.0
Structures completely isolated or exceeding at least twice the height of surrounding structures or trees
2.0
Table 2.6 Weighting factor E (type of terrain)
Type
of terrain
. Value of factor E
Aat land at any level
0.3 .
On hillside
1.0
On hilltop
1.3
..
2.2.7 Interpretation Of Overall Risk Factor. The risk factor method given in this Code Is Intended to give guidance on what can, in some cases. be a difficult problem. If the result obtained is considerably less ·than· 10-5 (1 in 100 000) then, in the absence of. other overriding considerations. protection does not appear necessary; if the result is greater than 10.5, say for example 10'" (1 in 10000), then sound reasons would be needed to support a decision not to give protection. When it is thought that the consequential effects will be small and that the effect of a lightning strike will most probably be merely slight damage to the fabric of the structure. it may be economic not to Incur the cost of protection but·to accept the risk. Even though this decision is .made, it is suggested that the calculatIon is stm worthwhile as givIng some idea of the magnitUde of the risk being taken'"
CP33: 1996
Structures are so varied that any method of assessment may lead to anomalies and those who have to decide on protection have to exercise judgement. For example, a steel framed buDding may be found to have a low risk factor but, as the addition of an air tennlnation and earthing system will give greatly improved protection, the cost of providing this may be consIdered worthwhile.
A low risk factor may result for chimneys made of brick or concrete. However, where chimneys are free-standing or where they project for more than 4.5 m above the adjoining structure, they will require protection regardless of the factor. Such chimneys are, therefore, not covered by the method . of assessment. Similarly, structures containing explosives or flammable substances are sUbject to additional consideration (see Section 5). Results of calculations for different structures are given in Table 2.7 and a specific case is worked through in Subclause 2.2.8. NOTE.
Table 2.7 should be read in conjunction with Figure 2.2.
2.2.8 Sample Calculation Of Overall Risk Factor. A hospital is 10 m high and covers an area of 70 m x 12 m. The hospital' is located on flat land and isolated from other structures. The construction is of brick and concrete with a non·metallic roof.
To determine whether or not lightning protection is needed. the overall risk factor is calculated. as follows: (a)
Number of flashes per km2 per year. The value for Ng is 12.6 flashes per km2 per year.
(b)
Collection area. Using the first equation in 2.2.2 the collection area, ~ in m2, is given by: Ae = (70 x 12) + 2(70 x 10) + 2(12 x 10)
A.c
(c)
+ (~x 100)
= 840 + 1400 + 240 + 314
Probability of being struck. Using the second equation in 2.2.2 the probable number of strikes per year, P. is given by:
P
= Ae x N9 x 100G
P = 2794 m 2 x 12.6 x 100G P (d)
= 3.5 x 10.2 approximately
Applying the weighting factors. The following weighting factors apply: factor A factor B factor C factor 0 factor E
= 1.7 = 1.0 = 1.7 = 2.0 = 0.3
The overall multiplying factor
=A x B x C x Dx E =
1.7
Therefore, the overall risk factor = 1.7 x 3.5 x 10.2 = 5.9510'2. The conclusion is, therefore. that protection is necessary.
35
CP33: 1996
2.3
NEED FOR PERSONAL PROTECTION
A hazard to persons exists dUring a thunderstorm. Each year. a number of persons are struck by lightning part.iculariy when outdoors in an open space such as an exposed location on a golf course, or when out on the water. Other receive electric shocks attributable to lightning when Indoors. In built-up areas protection is frequently provided by nearby buftdlngs, trees. power lines or street lighting poles. Persons within a substantial structure are normally protected from direct strikes. but may be exposed to a hazard from conductive materials entering the structure (e.g. power. telephone, or TV antenna wires) or from conductive objects within the structure which may attain different potentials. Measures for the protection of persons within buildings or structures are set out in Section 7. Ughtning strikes direct to a person or close by may cause death or serious injury. A person touching or close to an object struck by lightning may be affected by a side flash. or receive a shock due to step, touch or transferred potentials, as described in Appendix A. When moderate to loud thunder is heard, persons out of doors shOUld avoid exposed locations and should seek shelter or protection in accordance with the gUidance for personal safety provided in Appendix G, particutariy if thunder follows within 15 s of a lightning flash (corresponding to a distance of less than 5 km). 2.4
NEED FOR PROTECTION OF PERSONS AND EQUIPMENT WITHIN BUILDINGS
As explained in Clause 2.3, persons and equipment within buildings can be at risk from lightning currents and associated voltages which may be conducted Into the b\Jildlng as a consequence of a lightning strike to the building or associated services. Some equipment (e.g. electronic equipment, including computers) is especially susceptible to damage from overvoltages transferred from external connections caused by lightning and such damage may occur even when the lightning strike is remote from the building. e.g. from a surge conducted into the building via the power and telecommunication cables. Measures may therefore need to be taken to protect persons and equipment within buildings and Section Seven provides further. advice on this SUbJect. Tt:t~~~sures recommended in· Section . Seven can be implemented even when a lightning protection system for the building structure has not beerl. provided. . The decision as to Whether to provide protection specifically directed to equipment will depend on the value placed on that equipment and on the cost and inconvenience which might resuit from the equipment being out of service for an extended period. The risk factor determined from Clause 2.2 will provide guidance on the likelihood of a building being subject to a lightning strike with consequent risk of damage occurring to equipment within the bUilding. However. since damage to equipment can result from lightning strikes to adjacent properties or to power or signal lines some distance away. the Index value may not be a sufficient indicator of the risk. The incidence of damage occurring to similar equipment within bundings in the vicinity may provide . . a better guide to the need to protect.
'lI!1II1!
36
"
"•" •.-.
CP33: 1996
Reference (a I
{bl
General arrangement
Collection area and method of calculation
R15
1S
, ... ----..,..~ l I \ ---!I I :
I-
i~
~, I
..(
'--t-~'C. r'",._--t-.' 14 ....JQ...;
8
f,
R9 yoV ,
6
I ~9
e
j~6
I "'-1_-
. i.lJ
R6
r------' F W----lRb 60
r-
R6
,
-'
I
4
" ~ (
A e .. 7 X 8 + 216 X 71 + IIS 2 + + 10 tapprox.l (or areas in black A c .. 405 m'
~~~6
1b~~
(el
"-R1C.
ti"'o--~
R6--.
j"
....
A c .. n 14 2 + 2(14 x 30) A e .. 1456 m 2
" - - - - c;:--"[
(~~ 114
~
.,-t
~:: 21 ...... _--~~ 21 40 '21" I....I.. _1_ .., '--R21 I
10
j
- -
",
b
.....•.
A c • 15 X 40 + 2121 X 401 + +2(21 X 151 + ,,21 2 A c • 4296 m1
,
I- - -, .
.
W
I
..,--- -r..---. .. 2' ~-J [-'~,--tl~
R21---,.
21
t
ldl
I
fIlA
r15~-- ----t SO 15 K- R15
i--~ f " Ie)
~i-
L._ I
fIlA
·14 X 50 -t 2115 x 50) + +2(15X 14)+1115' A c " 3327 m 2 A~
1S 14 1S
""l
: Ll r- 6
SO
:
,
~.
6..J
6
6
:
25
I
2S
.. ,
A c • 25 X 60 + 25 X 30 + 6 X 60 + + 6 X 50 + 6 X 25 + 6 x 25 + + 6 X 30 + 6 X 24 + 5/411 6' A c " 3675 m2
1
,./
1--:to -j :tn 6
If)
(~
R'3~ r',
..t 3
-~t3.
+ 2(9} +
A~=9+2(9)
Ac
= 73.3
m2
:.i
All dimensions are in metres. NOTE. This fi9ure should be used in conjunction wilk lab Ie V
Figure 2.2 Details of structures and collection areas
-"
..
113
2
Table 2.7 Examples of calculations for evaluating the need for protection
1
2
Ref. in Figure 2.2
Description of structure
4
3
6
7
8
9
10
Weighting factors
RIsk of being struok, P
;
Collection area, Ate
(a)
5
Rash density, Ng
Acx Ng
X
B Type of construction (Table 2.3)
C
0
E
Use of structure (Table 2.2)
Contents or consequential effects (Table 2.4)
Degree of Isolation (Table 2.5)
Type of country (Table 2.6)
A
P= 10-8
11
12
13
Overall multiplying factor (prodUcts of columns 6 to 10)
Overall risk factor (product of columns 5 to 11)
Recommendation
3327
12.6
41.9 x 10'"
1.2
1.0
0.3
0.4
0.3
0.043
1.8 x 10-3
Protection recommended
An office building, built with reInforced concrete and Is havIng nonmetallic roof
4296
12.6
54.1 x 10-3
1.2
1.0
0.3
0.4
0.3
0.043
2.3 x 10-3
ProtectIon recommended
A school, built with reinforced concrete and brick and Is having non~ metallic roof
1456
1.0
1.7
0.4
0.3
0.35
6.4 x 10-3
Protection recommended
An apartment. built with reinforced concrete and brick and Is having nonmetallic roof
(b)
(c)
. 12.6
18.3x 10'"
1.7
Table 2.7 Examples of calculatIons for evaluating the need for protectIon
1
2
Ref. in Figure 2.2
Description of structure
4
3
5
6
7
8 Weighting factors
Risk of beIng struck, P
Collection area, "c
Aash density,
p=
Ng
Ae x Ng X 10.8
A two storey detached bungalow, built with reinforced concrete and brick and is having non· metallic roof
405
12.6
5.1 x 10.3
(e)
A factory, built with reInforced concrete and steel framed encased and is having metallic roof
3675
12.6
46.3 x 10'3
1.2
0.4
0.3
(f)
A security guard post of 3mx3mx 3m, built with reinforced concrete and brick and Is having metallic roof
73.3 ,
12.6
9.24 x 10'4
0.3
0.4
0.3
(d)
10
9
B
e
11
12
13
Overall multiplying factor (products of columns 6 to 10)
Overall risk factor (product of columns 5 to 11)
Recommendation
A Use of structure (Table 2.2)
Type of construction (Table 2.3)
C Contents or consequential effects {Table 2.4}
0 Degree of Isolation (Table 2.5)
Type of country (Table 2.6)
0.3
1.7
0.3
0.4
-0.3
0.02
1.02 x 10'4
Protection recommended
0.4
0.3
0.017
7.9)( 10.3
Protection recommended
0.4
0.3
0.00432
4 x 10.8
Protection not required
.
NOTE. The risk of being struck, P (column 5), is multiplied by the product of the weighting factors (columns 6 to 10) to yield an overall risk factor (column 12). This should be s compared with the acceptable risk (10' ) for guidance on whether or not to protect. Risks less than 10.5 do not generally require protection; risk greater than 10.4 require protection; for risks between 10'5 and 10-4 protection is recommended (see Subclause 2.2.3 to 2.2.8)
Uke/ihood
Task:
I
Risk Analysis for Lightning Safe.ty - Example: Mining Activities
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National Lightning Safety Institute
Analysis by: Approved by:
";';
-. ..s
Date: Date:
Job Steps
Potential Hazards
A - Certain B - Likely C - Possible D - Unlikely E - Rare
Level of Risk
H M L L L
l.':
C>
"0 0
.
...
0
"(;j>
~,
::?Z
::?Z,
N
M
"l:t
H H M L L
R H H M M
:.E c.
15
S
a.
ln); . . .. . . . . . .. ... . . Impulse current (limp):, defined 'by 'a curr~nt value (Ipeak), 'a 'charge' (Q) and a specific'energy (W/R).
National Lightning safety Institute 891 N. Hoover Ave .Louisville CO 80027
'
107
THREE STAGE SPD COMBINES GOOD PROPERTIES OF DIFFERENT PROTECTION DEVICES TO MANAGE AN INPUT TRANSIENT OPTIMALLY.
>---e--t
VOLTIOE
DROP
ELEMENT2
L\V1= R.i LIGHlNI
or AV1 = l.diJdt
TRANS
VOL11GEI CURRENT SOURCE STIOE2
MOVDSlI~
PR O'1"B:TED INPUT
SWE1
mlUlNCHE
DIODE (SAD)
-Problem: A lightning surge strikes a signal input in electronic equipment. This surge can be represented by a voltage/current source with the open-circuit voltage/short-circuit current characteristics of the combination wave of page 43. The surge energy is diverted to ground as folloWS: 0) Current will not flow until the input voltage reaches the SAD's clamping voltage. The open circuit 1,2150 f.lS voltage curve applies. 1) The SAD fires in about 1 ns and clamps the voltage at about 18V thus protecting the exposed input effectively. Short circuit 8120 Os current curve applies approximately. Since the SAD can dissipate only 1500 Watts (80 Amps). the rising current must be redirected to a second stage. 2) As a second stage a MOV is usually chosen to keep the clamping characteristic, preventing short circuit of the signal source at low energy transients. The current or the rate of rise of the current, which now is entirely circulating through the SAD. creates a voltage AV1 across the Voltage drop element 1. When the total voltage AV1+VSAD reaches the MOVs clamping voltage (about 27V) the current flows through the MOV, protecting thus the SAD. 3) The still rising surge current develops a voltage drop AV2 across element 2. When AV2+VMOV reaches the gas tube firing voltage the gas tube turns on and directs most of the extremely high lightning energy to earth ground. A 90V gas tube will fire at its rated voltage in about 1 s. But its firing voltage depends on the rate of rise of the 'applied voltage. During the very fast lightning transient it will fire at about 650V. Solution: The three-stage SPD combines the time response, clamping characteristics and energy handling capabilities of different devices ensuring effective input protection and avoiding protection device failure. Courtesy Profs. C. Brio:to tprd M.. Simon, Univ. de 111 Republica, Montevideo Uruguay
108
C C C C
«
SURGE REFERENCE EQUALIZER (SRE)
« «
SREs eliminate the threat of potential differences where data and AC power lines are remotely grounded. Power and data lines are connected to the SRE. The SRE is installed at the point of use of the equipment. SREs are available at most electronics stores.
« « « 4 C C C
C
100
Fuse TIp
•(
Power Sup pression
(
L TELEPHONE LINE
Gas
tube
.
N
G
Ring 100
Surge reference equalizer
Service. . panel
...
/
Branch circuit
Metal water pi pe
Telephone protectors
109
SURGE PROTECTION CHECKLIST 1.0 The following factors justify the suitability of SPDs: 1.1
Surge damage has been suffered or is suspected.
1.2 Surge damage has been suffered by other nearby facilities or organizations.
1.3 A Risk Analysis indicates significant probabilities. 1.4 The consequences of surge damage are serious, despite a low probability. 1.5
Surge protection is specified by an insurance company -or parent organization.
1.6 Experience with surge protection elsewhere has validated their application. 2.0 What should SPDs protect? 2.1
Main Entry Panel
2.2
Selected Branch Panels according to criticality.
2.3
Telephone Lines and Telephone Switch.
2.4 Cables for Telemetry, Instrumentation, and Control 2.5
Antenna Cables
2.6
Security and Fire Alarm Systems
2.7
Outdoor Lighting.
110
4 4 4 4 4
4
4 4
4 4
RECOMMENDED SPD SPECIFICATIONS
« NLSI applies the below criteria in assessing merits of protection devices:
surge
1. UL 1449 Listed under TVSS for load side installation AND UL
1449 Listed for Surge Arrestor for line side installation. 2. Replaceable MOV modules. No spark gaps with impulse breakdown voltages. No use of potting' compounds to encapsulate MOVs. 3. Environmentally-neutral materials with no off-gassing. 4. All mode protection L-N, L-G, N-G, L-L. 5. Internally-fused disconnects on each phase for means of circuit protection from failed components. 6. SPD passes tests per IEEE Std C6234 sub 7.5 and 7.5.4 for loss of neutral protection. 7. Cable connection between bus and SPD minimum # 8 AWG. 8. Enclosure all steel with UL-approved fasteners. 9. No power consumption. No follow-on current. 10. Response time less than one nanosecond. Self-restoring response.. 11. Bipolar operation. Clamping operation is the same· for external or internal transients. ' 12. Continuous self-monitoring with indicator lamps for each mode , and remote alarm relays in each phase. Audible' alarm .with push~ to-test and push-to-silence abilities. 13. Independent, certified test results furnished. 14. Manufacturer compliance with ISO 9000 QC procedures. 15. Meets all requirements of FAA. Accepted by FAA for high threat environments..
« « « « « 4
« « « « « « « « 4 4 4 -4·
4 4 4 4 4 '4 ~ ~.
National Ughtning safety Institute 891 N. Hoover Ave LoulsvUleCO 80627
~
4 4
4 4 4
111
RECOMMENDED SPD INSTALLATION PRACTICES 1. SPDS should be installed as close as possible to their respective panels. Inches instead of feet is the Rule. Lead length is critical for the SPD to operate efficiently. For example, a #6 AWG cable length of five feet causes a voltage drop of 275V. Where possible, mount the SPD directly against the panel to be protected. 2. Avoid tight bends. Follow the NFPA-780 eight inch Rule to minimize inductance. 3. Leads should be twisted to reduce magnetic coupling. Refer to FAA-OI9d, Table V, page 35 for details. 4. SPD remote monitoring alarms should be placed in a fullyoperational area, not in a closet or in an infrequently-visited equipment room. 5. SPDs should be inspected regularly. During the lightning season look them over daily. Smell smoke? Many SPDs work via failure. A burned SPD module should be replaced promptly.
National Lightning safety Institute 891 N, Hoover Avo louisville CO 80021
112
SPD EVALUATION FORM The following tables can be used to compare different TVSS products or to document the different lVSS device specifications for the correct application. Note: the numbers provided are example specifications, typical for TVSS devices intended for a staged application.
Specifications/features desired Sample
Hardwired TVSS Model 1 Model 2 Model 3
Sample
240V 300V
120V 150V
Protection modes
5
3
UL
approved
x
-x-
Let through voltage
750 V
330 V -
Warranty
5 Yr.
1 Yr.
Pricing
$250
$65
Application voltage MCOV Peak surge current Filter freq. range Energy rating Response time
Operational indicators Diagnostic indicators Overcurrent protection Alarms
Manufacturer name
Communications TVSS Sample Model 1 Model 2 Model 3 Application voltage MCQV.
240V 300V
P.eak surge current' Filter freq. range Energy rating Response time Protection modes
5
UL
approved
x
Let through voltage
750 V
O'perational indicators Diagnostic indic,ators Overcurrent protection Alarms Warranty
1 Yr.
Pricing
$250
" Manufacturer name
Receptacle TVSS Model 1 Model 2
Model 3
113
USEFUL SPD FOLLOW-UP REFERENCES
1. IEEE Std 1100-2005 Powering and Grounding Electronic Equipment, Institute of Electrical and Electronic Engineers, NY NY 2005
2.. Internet Web Sites: 2.1. www.polyphaser.com 2.2 www.phoenixcontact.com 2.3 www.mtlsurgetechnologies.com 3. EMCfor Systems and Installations, Tim Williams and
Keith Armstrong, Newnes·Publishers, London 2000 4. Noise Reduction Techniques in Electronic Systems, HenryW. Ott, John Wiley, NY NY 1988. 5. Protection ofElectronic Circuits from Overvoltage, Ronald B. Standler, John Wiley, NY NY 1989. 6. Recommended Practice for Protecting Residential Structures and Appliances Against Surges, EPRI PEAC Corporation, EPRI~ 1999
National Lightning safety Institute 891 N. Hoover Ave Louisville CO 80027
Ode to the Missing Surge Protector Author Unknown, Supplied by National Lightning Safety Institute www.Iightningsafety.com
If a transient hits a pocket on a socket on a port And the bus is interrupted at a very last resort And the access ofthe memory makes your floppy disc abort Then the shocked packet pocket has an error to report. Ifyour cursor finds a menu item followed by a dash And the double-clicking icon puts your window in the trash And your data is corrupted 'cause the index doesn't hash Then your situations' hopeless and your system's gonna crash. Ifthe label on the cable on the table at your house Says the network is connected to the button on your mouse But your packets want to tunnel to another protocol That's repeatedly rejected by the pririter down the hall And your screen is all distorted by the side effects of gauss So your icons in the window are as fickle as a grouse Then you may as well reboot and go out with a bang 'euz sure as I'm a poet, the sucker's gonna hang.
National Lightning Safety Institute 891 N. Hoover Ave
louisville CO 80027 .
115
INTENSIVE WORKSHOP, LIGHTNING PROTECTION FOR ENGINEERS
Chapter Six
COMMUNICATIONS FACILITIES, EXTERIOR LIGHTNING PROTECTION
116
" •
•• .,.
.
" ,.,. ", ",
Chapter Six Overview
~etY applicati?D, Communications facilities often have a critical life..$ lie broadcasting especi~ly wit? E911, air traffic control and some on some .levels operations. This Chapter and the following Chapter 7 fo~ " for Engmee!s. of detail not contained elsewhere in Lightning ProtectiIJ can be applied However, many of the principles in these two ctmpte.t6 generally to other facilities. . ... . COnsider vari~us t Extenor lightnlng protection of communications SItes muS OiDg and bondmg ~esigns of towers, adjacent equipment buildings and grouJJ ~ce cannot be ISsues at both locations. Regular inspection and maintc ignored without peril. ent Installations Motorola R56 Quality Standards for Fixed Network EquiP'" is a recommended follow-up to information herein.
pll::S
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117
TOWER BONDING - SELF SUPPORTING TOWER
Grounding KM
I - ~ Grounding Kit
..
To Central Office
J ,
..
2 1001 (0.6 me'.r) minimum below graoe To Central Ground Field
116 Bare Copper
ClAOUHDIlOD_
National Lightning Safety Institute 891 N. Hoover Ave louisville CO 80027
."
118
TOWER BONDING - GUYED TOWER
BOND TO SHI8.0
BONO GUYS TOGETHER
AND TO A GROUND ROD
IfSBARE COPPER
TO CO GROUtJO FIB.O
•
•• •• •• ,• •• •• •• •• •• •• •• •• •• •• ~ ~ ~ ~
f f f
4 National lightning
Safety lnatftute 891 N. Hoover Ave louisville CO 80027
• • • _ _ 0.
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. _ - _• • • • '"
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119
TOWER BONDING - BUILDING MOUNTED
' - - - Grounding Kits
DOD DOD
.....- - '2 Copper
....
To Central Office GroUnd Field
National lightning
safety InStitute 891 N. Hoover Ave Loulaville CO 80027
120
GUYED TOWER WITH EQUIPMENT BUILDING, GROUNDING CONFIGURATION
llnnBd AWG #2 solid or -.rancl811.nol>-InSutalllcl _ _ _ copperwue
TInned AWG #2 lOUd or
IUandad. non·inlulaled c:opperwite
~r
8
~--1~
__
ExltmII bUM bar 1II f1l\Iy point ClQIlIMC:Ied 10 lI>Cltmal ground ring UIlng lIMed AWG "2 ,olill or nandad, non-lnlutaled c:opPt' wira.
Grounding Guy Wires at anchors:
MONOPOLE TOWER WITH EQUIPMENT BUILDING, GROUNDING CONFIGURATION
llnnacl AWG ;n IOIld or llranded, non-insulated c:opper wlr1I
building
121
OPTIMUM GROUNDING DESIGN SHOWING PERFORMANCE WITH LIGHTNING ATTACK (Source: Polypbaser Corp.)
Recommended site grounding system about to be hit by lightning.
On a well designed ground system, the strike energy spreads out initially from the building.
Neglecting the coax currents, the strike energy moves outward from the tower base along the radial line.
As It spreads, " loses energy due to the spreading and I·R losses.
+--f--G""""OAOOS
""LIN
ENTR'f
As it reaches and saturates the radial system, It will traverse the building perimeter.
By the time It surrounds the building, the radials have spread out much of the energy.
122
TYPICAL COMMUNICATIONS SITE, EXTERIOR GROUNDING PLAN Pt.ANE MESH Sl7f.lSPACING BE MINIMAL SIZE PHACTICAL
.---_ EOUIPOTENTIAL S~IOULO
·STnUCTUUE
,
.,",
.-'
/f,
~
~
' J~r
K. .
METAL PIPES ENTERING
THE fACILITY-SHOULD GROUNDED AT TilE
, /
I ...... '-
.
B~' ".,. I ,JJ,
FACILITY ENTRY POINT
'~.., ,
,,\
"
\)
~/EA/R"T'tf
/" ,. ...... ,
f,
I"""
Y
I
/"
,
~"
,. ....
El.ECTRODE SUOSYSl EM ' ./" ROUNDING Fon fOlJlPOTENT~ LANE
·--·GHOUN[)ING FOH S TRucn JHf\L
STEEL
National Lightning safety Institute . 891 N. Hoover Ave Louisville CO 80027
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123
EXAMPLE OF EXTERIOR GROUNDING RING (ALSO CALLED COUNTERPOISE)
nNNED AWG 11'2 SOUD OR STRANDED NON-INSULAlED COPPeR
----------
GENERATOR
~X X ..,j... "
'l'
" "
)K I
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X X X X X X X X X X AlR CONOlnONER
~ X X X X X 2oC![mljectingle~:lXj crs ent;;trmtmg from tht, ground or One of these leaders meets one of the branches of the downward,propa. gating JearJt'f and establishes II path between cloud and gmlWtt Figure I shows a slrnpiilied picture nflightniog attachment to tlstnlct'urt: that is protected bjf cwrWf'ntiloua! lightning pf()teclion sy·s. tern cmpJnying air terminals in the limn (lfljghtning rmk "Vve om,' the models iJrvo,!w::{j
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CODE OF PRACTICE FOR
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SASS 03·1985
Code of Practice for
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INSTALLATION OF UGHTNlNG PROTECTION SYSTEMS 1.3 Listed. Labeled, or Approved Components. Where fit· tings, devices, or other components required by this standard are available as listed or labeled, such components shan be used,
NFPA780
Standard for the
Installation of lightning Protection Systems
1.4 Mechanical Execution of Work. Lightning protection systems shall be installed in a neat and workmanlike"manner.
2004 Edition
1.5* Maintenance. Recommended .,.", . nance of the lightning pr""~ the owner at the ,.~
document made
IMPORTANT NOTE: This NFPA is available for use wbjeet wimportant notices and legal disclai#let'$. These notices and disclaimers appear in all publicationl containing this document 1.6~"''' and ~ be found under the heading "Important Noncu and ~~. . O~ claimers Concerning NFPA Documentl. It They can also h# .' O~ 11.'
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r 0 ra h A re.eren, on r pa grap cted from another NFPA indicates mat document, As ...e user, the complete title and edition of the source ulJcuments for mandatory extracts are given in Chapter 2 an? ~ose for nonmandatory extracts. are giv~n in Annex N. Edltonal changes to extracted materIal consIst of revising references to an appropriate division in this document or the inclusion of the document number with the division number when the reference is to the original document. Reques~ for interpretations or revisions ofextracted text shall be senUo the technical committee responsible for the sOUl"ce document. Information 011 referenced publications can be found in Chapter 2 and Annex N.
Chapter 2 Referenced Publications
2.1 General. The documents or portions thereof listed ill this chapter are referenced within this standard and shall be con· 'd d f . . Sl ere part 0 the requIrements of thiS document. 2.2 NFPA Publication. National Fire Protection Association, 1 Batterymarch Park, Quincy, MA 02169·747l. NFPA 70 National Electrical Cork~ 2002 edition, . ' , 2.3 Other Publications. (Reserved)
Chapter 3 Defmitions 3.1 General. The definitions contained in this chapter shall apply to the terms used in this standard. Where terms are not included, common usage of the terms shall apply.
ls.2 NFPA Official Definitions.
Chapter 1 Administration 1.1 Scope. 1.1.1 This document shall cover traditional lightning protection system installation requirement5 for the following: (1) Ordinary structures
(2) (3) (4) (5)
Miscellaneous structures and special occupancies Heavy-duty SlaCks Watercraft Structures containing flammable vapors, flammable gas~s, or liquids that give off flammable vapors
. . . 1.1.2* This document shall not cover lightning protection system ins~lIation requirements for the following: (1) Explosives manufacturing buildings and magazines (2) Ele~tric generating, transmission, and distribution systems . . . 1.1.3 This document shall not cover lightning protection system installation requirements for early streamer emission systems or charge dissipation systems. 1.2 Pwipose. The purpose of this standard shall be to provide for the;safeguarding of persons and property trom hazards arising from exposure to lightning.
2004
Edl~on
3.2.1* Approved. Acceptable to the authority havingjurisdiction. 3.2.2* Authority Having Jurisdiction (AHJ). An organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment. materials, an installation, or a procedure. 3.2.3 Labeled. Equipment or materials to which has been at· tached a label, symbol, or other identifYing mark of an organization that is acceptable to the authority having jurisdiction and concerned with product evaluation, that maintains periodic inspection of production of labeled eqUipment or materials, and by whose labeling the manufacturer indicates compliance with appropriate standards or perfonnance in a specified manner. 3.2.4* Usted. Equipment, materials, or services included in a list published by an organization that is acceptable to the au· thority having jurisdiction and concerned with evaluation of prodUCts or services, that maintains periodic inspection of production oflisted equipment or materials or periodic evaluation of services, and whose listing states that either the equipment, material, or service meets appropriate designated stan· dards or has been tested and found suitable for a specified purpose.
239
NCM®
GUIDELINE 1d Lightning Safety July 1997·
Re~sed
June
The NCM Committee on Competitive Safeguards and Medical Aspects of Sports acknowledges the significant input of Brian L. Bennett, formerly an athletic trainer with the· College of William and Mary Division of Sports Medicine, Ronald L. Holle, a meteorologist, formerly of the National Severe Storms Laboratory (NSSL), and Mary Ann Cooper, MD, Professor of Emergency Medicine of the University of Illinois at Chicago, in . the development of this guideline.
Lightning is the most consistent and significant weather hazard that may affect interc01{egiate athletics. Within the United States, National Oceanographic and Atmospheric Administration (NOAA) estimates that 60-70 fatalities and about 10 times as many injuries occur from lightning strikes every year. While the probability of being struck by lightning is low, the odds are significantly greater when a storm is in the area and proper safety precautions are not followed.
2006~~~~~~~~~~~~~~~~_
1. Designate a person to moni- 4. Know where the closest tor threatening weather and to safer structure or location" is to make the decision to remove a the field or playing area, and know team or individuals from an athlet- how long it takes to get to that ics site or event. Alightning safe- location. Asafer structure or locaty plan should include planned tion is defined as: instructions for participants and a. Any bUilding normally occuspectators, designation of warning pied or frequently used by peoand all clear signals, proper sigple, Le., a building with plumbnage, and designation of safer ing and/or electrical wiring that places for shelter from the lightacts to electrically ground the ning. structure. Avoid using the 2. Monitor local weather reshower or plumbing facilities ports each day before any practice and contact with electrical applior event. Be diligently aware of ances during athunderstorm. potential thunderstorms that may b. Small covered shelters are form during scheduled intercollenot safe from lightning. Duggiate athletics events or practices. outs, rain shelters, golf shelters, Weather information can be found and picnic shelters, even jf they through various means via local are properly grounded for .television news coverage, the structural safety, are usually not Internet, cable and satellite weathproperly grounded from the er programming, or the National effects of lightning and side Weather Service (NWS) homeflashes to people. They are page at http://www.weather.gov. usually very unsafe and may 3. Be informed of National actually increase the risk of Weather Service (NWS) issued lightning injury. Other dangerthunderstorm "watches" or warnous locations include areas ings," as well as the warning signs connected to, or near light of developing thunderstorms in poles, towers and fences that the area, such as high winds or can carry anearby strike to peodarkening skies. A watch" means ple. Also dangerous is any conditions are favorable for severe location that makes the person weather to develop in an area; a the highest point in the area. "warning" means that severe c.ln the absence of a sturdy, weather has been reported in an frequently inhabited building, area and for everyone to take the any vehicle with a hard metal proper precautions. A NOAA roof (neither aconvertible, nor a weather radio is particularly helpgolf cart) with the windows shut ful in providing this information. II
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Education and prevention are the keys to lightning safety. The references associated with this guideline are an excellent educational resource. Prevention should begin long before any intercollegiate athletics event or practice by being proactive and having a lightning safety plan in place. The following steps are recommended by the NCAA and NOAA to mitigate the lightning hazard:
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provides a measure of safety. The hard metal frame and roof, not the rubber tires is what pro~ tects occupants by dissipating lightning current around the vehicle and not through the occupants. It is important not to touch the metal framework of the vehicle. Some athletics events rent school buses as safer shelters to place around open courses or fields.
C. The existence of blue sky and the absence of rain are not guarantees that lightning will not strike. At least 10 percent of lightning occurs when there is no rainfall and when blue sky is often visible somewhere in the sky, especially with summer thunderstorms. Lightning can, and does, strike as far as 10 (or more) miles away from the rain shaft.
5. Lightning awareness should
phones, except in emergency situations. People have been killed while using alandline telephone during a thunderstorm. Cellular or cordless phones are safe alternatives to a landline phone, particularly if the person and the antenna are located within a safer structure or location, and if all other-precautions are followed.
be heightened at the first flash of lightning, clap of thunder, and/or other criteria such as increasing winds or darkening skies, no matter how far away. These types of activities must be treated as a warning or l(wake~up call" to inter~ collegiate athletics personnel. Specific lightning safety guidelines have been developed with the assistance of lightning safety experts: a. As aminimum, lightning safe-
ty experts strongly recommend that by the time the monitor observes 30 seconds between seeing the lightning flash and hearing its associated thunder, all individuals should have left the athletics site and reached a safer structure or location.
b. Please note that thunder may be hard to hear if there is an athletics event going on, particularly in stadia with large crowds. Implement your lightning safety plan accordingly.
d.Avoid using landline tele-
e. To resume athletics activities, lightning safety experts recommend waiting 30 minutes after both the last sound of thunder and last flash of lightning. If lightning is seen without hearing thunder, lightning may be out of range and therefore less likely to be asignificant threat. At night. be aware that lightning can be visible at a much greater distance than dur~ ing the day as clouds are being lit from the inside by lightning. This greater distance may mean that the lightning is no longer a significant threat. At night, use
both the sound of thunder and seeing the lightning channel itself to decide on re-setting the 30~minute "return-to-play" clock before resuming outdoor athletics activities.
f. People who have been struck by lightning do not carry an electrical charge. Therefore, cardiopulmonary resuscitation (CPR) is safe for the responder. If possible, an injured person should be moved to a safer location before starting CPR. Lightning-strike victims who show signs of cardiac or respiratory arrest need prompt emergency help. If you are in a 911 community, call for help. Prompt, aggressive CPR has been highly effective for the survival of victims of lightning strikes. Automatic external defibrillators (AED's) have become a common, safe and effective means of reviving persons in cardiac arrest. An AED should be considered as part of your sideline equipment. However, CPR should never be delayed while searching for an AED. Note: Weather watchers, realtime weather forecasts and commercial weather~warning devices are all tools that can be used to aid in decision-making regarding stoppage of play, evacuation and return to play.
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DESIGN LIGHTNING SAFETY FOR THESE SITUATIONS: 1. Self-supporting 150 ft. cellular radio tower. Equipment building 6X6XI0 is 15 ft. away. Radio equipment in building. Cable tray. Overhead incoming AC power. Gated fence. Perimeter light masts.
2. Guard shack 12X12X12, manned 24 X 7. Peaked roof. Drive through gates. High mast lighting. Radio antennas on building. AC power and telecomm inside. Air conditioning box on roof.
3. Row of six Earth Covered Explosive Storage Magazines each 20X40X15. Roll-up doors. Interior crane. Ventilation Stacks. High mast lighting. Perimeter fence.
4. Wastewater treatment plant. Three adjacent 100 ft. diameter uncovered steel tanks. Incoming AC power and telecom. Pumps, valves, relays, switches. Steel catwalks to all structures. Guyed radio tower 20 ft. high. Fenced.
5. Three story computer center building with flat roof. Many metal boxes on roof for water chilling, HVAC, pumps, fans, motors. 175 employees. Lighted parking lot. Trees. Picnic and recreation area outside. Secondary building 1OXI OXl 0 sharing AC power & telecomm 30 ft. away.
6. Metal shelter used as bus stop 10XIOXlO open on one side. No power. Telephone pole carrying AC power, cable and telephone services adjacent to shelter.
7. Wooden shelter on golf course 1OXl OXI 0 with four posts supporting peaked roof. Interior lights. Pop machine. Water fountain. Picnic table.
8. Industrial cement plant on five acres. Fenced. Some permanent buildings. 125 outdoor and indoor workers, 2 shifts. You are the Safety Manager. Develop a program for lightning safety for people and for electrical/electronic equipment.
Ml'11OtW. UGH1'NNG SAFETY NmIU1'E 8t1 North·fio«w8r 1we.
1OI• • co 80021-2214
242
Anonymous Critique for Workshop 1. The information presented to me was: a. Useful and applies to my work _ b. Not relevant. Needs revision ~~_------c. Too technical_. Incomplete _ _' OK, except for _ d.Other _
2. The best part of the course was: 3. The worst part of the course was: 4. Some information I need which was missing was:
_
5. The top three things I'll remember about the course are:
a.
_
b.
_
c.
,.-;...'
_
6. I rate the instructor as follows on a 1-10 scale: Good Presenter of Information (GPI); Knew Subject (KS); Give any constructive comments,too. a. GPI
=
_
---------------------
KS= Other=
_
7. The meeeting room arrangement, choice of location,' and general logistics were OK _ ; need improvement: _ 8. Cost of the seminar was: a. about right _ b. too high_ c.other
_
9. Workbooks, handout materials and visual aids were: a. Good. . Just Fair _ . OK _ _ b. Improvements Suggested _ __ _ . - - - - - - - - - 10. Others in my organization or in my industry williwill not find the Workshop beneficial. 11. There is a one day class on Inspection, Maintenance and Testing of the LPS. Would other people in your organization be Interested? (See instructor here.) 11. Other comments and opinions:
243
technical bookfrom ... NATIONAL LIGHTNING SAFETY INSTITUTE (NLSI) www.lightningsafety.com
It LIGHTNING PROTECTION FOR ENGINEERS An Illustrated Guide in Accord with Recognized Codes & Standards TABLE OF CONTENTS, Revision 3. August 2006 Part J
Lightning Physics, Lightning Behavior and Lightning Safety Overview
Part 2
Risk Assessment
Part 3
The Grounding and Bonding Imperative
Part 4
Exterior Lightning Protection for Structures
PartS
Interior Lightning Protection for the Electrical System Of a Complex Facility
Part 6
Communications Facilities, Exterior Lightning Protection
Part 7
Communications Facilities, Interior Lightning Protection
Part 8
Lightning Protection for High Risk Installations Containing Sensitive Electronics, Explosives, Munitions, or Volatile Fuels
Part 9
International Views of Unconventional Air Terminal Designs Such As ESE and CTSIDAS
Part 10
Lightning Safety for Outdoor Workers
Part JJ
References, Resources and Codes
COST IS $79.95 + $5.00 S&H anywhere in the USA. International (overseas) express carrier delivery is available. Contact us at Tel. 303-666-8817; Fax 303-666-8786; Email:
[email protected] , or you can mail this Order Form to: NLSI, 891 N. Hoover Ave., Louisville CO 80027-2294
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244
•
• • LIGHTNING PROTECTION FOR ENGINEERS - Page Index 1. Lightning Physics, Behavior and Safety Overview Chapter Overview The Convection Process Typical Waveform "Cold" vs "Hot" Lightning Log Normal Distribution Sequence of Steps in Typical Flash Streamer/Leader Lightning Behavior - Part 1 Lightning Behavior - Part 2 ACR Resistive, Magnetic & Electric Fields The Attachment Process TD/YR Worldwide Map TD/YR USA Map FDNRlSQIKM USA Little-Known Information Per NASA - The Protection Process Per NLSI - How to Get to Lightning Safety Matrix of Protection Sub-Systems Lightning Mitigation Guideline
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
2. Risk Assessment Chapter Overview Determining the Probabilities... Analysis ofNeed for Protection NLSI Version of Risk Assessment
23 24 25-28 29-39 40
3. The Grounding & Bonding Imperative Chapter Overview Definition of Terms Factors Affecting Soil Resistivity
41 42 43-45 46
•~ f f f ~ ~ ~ ~
f ~
245
Types of Earth Electrode Systems Various Grounding Layouts Grounding Buildings with Basements Grounding Buildings without Basements Ground Rod Bonding Grounding Additives and Backfills Bonding Drive & Walk Gates Bonding to Fence Post "Ufer" Ground Detail Separation Distance, Grounds-to-Other Conductors Service Entry Grounding Problem with Poor Bonding Facility Bonding Detail 1 Facility Bonding Detail 2 Bonding Building Steel to Ground Ground Potential Equalization Bonding Separate Ground Rods Bonding Conduits Bonding to Prevent Side Flashing Miscellaneous Bonding Examples (MBE) 1 MBE2 MBE3 MBE4 MBE5 Hierarchy of Bonding Jumpers Bonding Jumper Inductance Bonding Technique Effectiveness Typical Connector Tenninations Bonding Inspection Checklist 4. Exterior Lightning Protection for Structures Chapter Overview Approved Air Tenninal Designs Personal Shelter, Faraday Cage Concept Free-Standing Steel Masts Overhead Wire (OHW) or Catenary Design Franklin Rods 1
47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69
70 71 72 73 74 75 77 78 79 80 81
82 83
246
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~.
Franklin Rods 2 Franklin Rods 3 Function of Overhead Shield Wire (OHW) Design OHW - View 1 Design OHW - View 2 Design OHW - View 3 OHW Support Poles Details Preference for Mast & OHW per Codes Cone of Protection (CP) Model Rolling Sphere (RS) Model Comparison ofCP and RS
84 85 86 87 88 89 90 91 92 93 94
5. Interior Lightning Protection for the Electrical System Of a Complex Facility Chapter Overview Side Flash and Coupling to Building Wiring SPD Locations per IEEE SPDs Typical for Commercial Building SPDs Typical for Process Control Plant Worst Cases of Transient Insults Voltage and Current Waveforms Overview of SPD Functions Transient Limiting of Generic SPD Components Advantages & Disadvantages of SPD Components Desirable SPD Operating Characteristics Three Stage SPD Example Surge Reference Equalizer Surge Protection Checklist Recommended SPD Specifications SPD Installation Practices SPD Evaluation Form SPD Follow-Up References The Missing Surge Protector
95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114
6. Communications Facilities, Exterior Lightning Protection Chapter Overview Tower Bonding - Self Supporting Tower
115 116 117
~4{
Tower Bonding - Guyed Tower Tower Bonding - Building Mounted Tower Grounding Configurations Optimum Grounding Under Lightning Attack Exterior Ground Plan Exterior Ground Ring Coaxial Cable Routing Bonding Coaxial Cable Shield Coaxial Cables Entering Building Grounding Checklist, Exterior
118 119 120 121 122 123 124 125 126 127
7. Communications Facilities, Interior Lightning Protection Chapter Overview Typical Interior Grounding Plan "Halo" Ground Examples of Interior Grounding & Bonding Bonding Raised Floor Bonding Interior Metallic Components Cabinet & Rack Bonding Cable Tray Bonding Details of Cable & Duct Bonding Grounding Checklist, Interior SPD & UPS Layout Typical SPD Applications SPD Checklist SPDs - Satellite Systems SPDs for Computers & CCTV Systems SPDs for LAN Systems Alternative Methods of Shielding Bonding Cable Shields Noise Reduction 1 Noise Reduction 2
129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149
8. Lightning Protection for High Risk Installations such as Electric Power Facilities, Explosives, Munitions & Volatile Fuels Chapter Overview
151 152
248
Decision Tree for Facility Lightning Safety Principles of Topological Shielding Fortress or Zone Protection Concept Preference for Mast or OSW Air Terminal Designs Errors at Critical Facilities, Parts 1 & 2 Errors at Critical Facilities, Parts 3 & 4 Going Beyond The Codes
153 154 155 156 157
158 159162
21 st Century Lightning Safety for Environments Containing Sensitive Electronics, Explosives, And Volatile Substances
163-
168 Attention to Detail 9. International View of Unconventional Air Terminals Such as "ESE" and "CTS/DAS." Chapter Overview Peer-Reviewed Technical Papers (3 Abstracts) Email from Malaysia Email from Turkey USA Court Case Concerning ESE Profs. Uman & Rakov Paper on "CTS/DASIESE" Warning of the ICLP Scientific Committee
169
171 172
173 174
175 176 177188 189-
194 10. Lightning Safety for Outdoor Activities Chapter Overview . Decision Tree for People Lightning Safety Lightning As It Originates From Clouds Pour Mechanisms of Lightning Attachment Touch and Step Potentials Instantaneous Potential Differences .. Lightning Deaths by State (1) Lightning Deaths by State (2) After Effects to Lightning Survivors Sample Policy Statement for Lightning Safety
195 196
197 198
199 200 201 202 203 204 205
Sample Poster for Outdoor Workers Sample Poster for Outdoor Recreation Sample Poster for Swimming Pools Sample Poster for Athletic Fields Sample Lightning Safety Messages Safe Shelters - Faraday Like Cage Overview of Lightning Detection Equipment
11. References, Resources and Codes Chapter Overview Glossary of Lightning Terms Annual USA Lightning Costs & Losses Helpful Lightning URLs
Review of Country Codes and the IEC 62305 Examples of Selected Codes (Cover Pages Only) IEC 62305 (www.iec.ch) AustralialNew Zealand AS/NZ 1768 British BS6651 China GB 50057-94 India IS 2309 Russia RD 34.21.122-87 Singapore CP 33 South Africa SABS 03 USA NFPA-780 USA NCAA Guideline ld Quiz - Design LPSs for Various Situations NLSI 2 Day Class Critique LP ENG Book Order Form Page Index
206 207 208 209 210 211 212213 215 216 217224 225 226227 228 229 230 231 232 233 234 235 236 237 238 239240 241 242 243 244249
SIX STAGES OF A PROJECT
1. ENTHUSIASM 2. DISENCHANTMENT 3. PANIC 4. SEARCH FOR THE GUILTY 5. PUNISHMENT OF THE INNOCENT 6. PROMOTION FOR THOSE NOT INVOLVED
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