December 2006
1
Bulletin No 147/2006
INTRODUCTION
Four persons have been fatally injured by lightning strikes during the past two years within the Group. The
purpose of this bulletin is to provide guidance on protection against the risks of lightning. It covers:
a. An understanding of the risks of lightning, including how lightning develops, the characteristics
of lightning, warning signs of danger and victims of lightning strikes.
b. Lightning safety, including lightning safety policy, safety plan, decision tree, advance warning,
notification, and evacuation.
c. Further guidelines on personal lightning safety, an overview of lightning detection equipment
and good lightning shelters are appended.
The intent is that operations may use the included to distil appropriate site specific Lightning Safety Plans.
Issued by the Anglo Technical Division
The information contained in this document is not prescriptive. It is indicative of good practice and is intended as information for site specific interpretation and application by the
responsible parties within the Anglo American plc Group. The material contained herein is based on information believed to be reliable, however, no representation or warranty,
express or implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its subsidiaries or associated companies for
any loss or damage of whatsoever nature arising out of the use of, adherence to or the lack thereof to any part of this information.
ATD, VOHE
Tel:
+27 11 638 3045
th
Administrative Contact:
5 Floor, 45 Main Street
Fax:
+27 11 638 2610
Marshalltown, Johannesburg
e-mail: [email protected]
CONTENT
1
INTRODUCTION ................................................................................................................................ 1
2
UNDERSTANDING LIGHTNING ....................................................................................................... 3
2.1
How Lightning Works................................................................................................... 3
2.2
The Warning Signs ...................................................................................................... 3
2.3
How Lightning Develops Between The Cloud And The Ground.................................. 3
2.4
Thunder ....................................................................................................................... 4
2.5
Negative Lightning And Positive Lightning .................................................................. 4
2.6
Facts About Lightning.................................................................................................. 4
2.7
Lightning Can Strike “Out of the Blue”......................................................................... 4
2.8
Lightning Strikes Anywhere ......................................................................................... 5
2.9
A Near-Miss Can Be Deadly........................................................................................ 5
2.10
The Effects Of Lightning .............................................................................................. 6
2.10.1 Signs/Symptoms.......................................................................................................... 6
2.10.2 Care............................................................................................................................. 6
3
LIGHTNING SAFETY ......................................................................................................................... 6
3.1
Policy and procedures ................................................................................................. 6
3.2
Decision Tree .............................................................................................................. 7
3.3
Advance Warning of the Hazard.................................................................................. 7
3.3.1
The 30/30 rule ............................................................................................................. 7
3.3.2
Weather network information....................................................................................... 7
3.3.3
Lightning detectors ...................................................................................................... 8
3.4
Notification Of Affected Persons.................................................................................. 8
3.5
Evacuation To Safe Shelters ....................................................................................... 8
4
REFERENCES................................................................................................................................... 9
Appendix 1: PERSONAL LIGHTNING SAFETY ..................................................................................... 10
Step 1: Planning ...................................................................................................................... 10
Step 2: Establish the danger ................................................................................................... 10
Step 3: Inside the shelter......................................................................................................... 10
If Outdoors:.............................................................................................................................. 11
An imminent strike................................................................................................................... 11
Lightning strike victims: ........................................................................................................... 11
Appendix 2: AN OVERVIEW OF LIGHTNING DETECTION EQUIPMENT............................................. 12
1. Examples of some of the systems available on the market.............................................. 13
2. Features of lightning detectors. ........................................................................................ 14
Appendix 3: Good Lightning Shelters For Outdoor Workers ................................................................... 15
1. Summary .......................................................................................................................... 15
2. Behavior of lightning on struck objects ............................................................................. 15
3. Safe and not safe structures ............................................................................................ 15
4. Shelters Unprotected from Lightning ................................................................................ 15
5. Protected Shelters............................................................................................................ 16
6. Shelter placement on properties ...................................................................................... 16
7. Conclusion........................................................................................................................ 17
Examples of shelters for Lightning Protection ........................................................... 17
Page 2 of 17
2
UNDERSTANDING LIGHTNING
Lightning is a random, chaotic and dangerous fact of nature and it is an underrated
weather hazard
2.1
How Lightning Works
Lightning is a form of electrical discharge between clouds
or between a cloud and the ground. The discharge may
take place between two parts of the same cloud, between
two clouds, or between a cloud and the ground. Lightning
may appear as a jagged streak, a flash in the sky, or in the
rarer form of a brilliant ball.
Lightning is caused by the attraction between positive and
negative charges in the atmosphere, resulting in the
buildup and discharge of electrical energy. During a storm,
raindrops can acquire extra electrons, which are
negatively charged. These surplus electrons seek out a
positive charge from the ground. As they flow from the
clouds, they knock other electrons free, creating a conductive path. This path follows a zigzag shape
that jumps between randomly distributed clumps of charged particles in the air. When the two charges
connect, current surges through that jagged path, creating the lightning bolt.
Ice in a cloud seems to be a key element in the development of lightning. Storms that fail to produce
quantities of ice may also fail to produce lightning. In a storm, the ice particles vary in size from small ice
crystals to larger hailstones, but in the rising and sinking motions within the storm there are a lot of
collisions between the particles. This causes a separation of electrical charges. Positively charged ice
crystals rise to the top of the thunderstorm, and negatively charged ice particles and hailstones drop to
the middle and lower parts of the storm. Enormous charge differences (electrical differential) develops.
2.2
The Warning Signs
High winds, rainfall, and a darkening cloud cover are the warning
signs for possible cloud-to-ground lightning strikes. While many
lightning casualties happen at the beginning of an approaching
storm, more than 50 percent of lightning deaths occur after the
thunderstorm has passed. The lightning threat diminishes after
the last sound of thunder, but may persist for more than 30
minutes. When thunderstorms are in the area, but not overhead,
the lightning threat can exist when skies are clear.
2.3
Stepped leader moves
progressively from cloud
to ground and can follow
one or several paths
How Lightning Develops Between The Cloud And
The Ground
A moving thunderstorm gathers another pool of positively
charged particles along the ground that travel with the storm. As
the differences in charges continue to increase, positively
charged particles rise up taller objects such as trees, houses, and
telephone poles. Have you ever been under a storm and had your
hair stand up? Yes, the particles also can move up a person! This
is one of nature's warning signs that say you are in the wrong
place, and you may be a lightning target!
The negatively charged area in the storm will send out a charge toward the ground called a stepped
leader. It is invisible to the human eye, and moves in steps in less than a second toward the ground.
When it gets close to the ground, it is attracted by all these positively charged objects, and a channel
develops. The electrical transfer in this channel is seen as lightning. There may be several return
strokes of electricity within the established channel that you will see as flickering lightning.
Page 3 of 17
2.4 Thunder
The lightning channel heats rapidly and the explosive
expansion of heated air causes sound waves heard as
thunder. Since light travels faster than sound in the
atmosphere, the sound will be heard after the lightning flash. If
lightning is seen and heard at the same time, that lightning is
close by!
2.5 Negative Lightning And Positive Lightning
Not all lightning forms in the negatively charged area low in
the thunderstorm cloud. Some lightning originates in the cirrus
anvil at the top of the thunderstorm. This area carries a large
positive charge. Lightning from this area is called positive
lightning. This type is particularly dangerous for several
reasons. It frequently strikes away from the rain core, either
ahead or behind the thunderstorm. It can strike far from the storm, in areas that most people do not
consider to be a lightning risk area. The other problem with positive lightning is it typically has a longer
duration, so fires are more easily ignited. Positive lightning usually carries a high peak electrical current,
which increases the lightning risk to an individual.
2.6 Facts About Lightning
• One ground lightning strike can generate an electric charge of 100 million to 1 billion volts.
• Lightning can carry a current of between 25,000 to 250,000 amps (by comparison, a typical
household outlet is 10 amps of current and the heart can be stopped by 0.01amps).
• The temperature of a typical lighning bolt is 30,000oC - hotter than the surface of the sun.
• Lightning strikes create powerful radio waves.
• Some 40% of lightning is forked with two or more ground attachment points.
• Most lightning strikes occur either at the beginning or end of a storm.
• Storms can grow from the small towering cumulus stage to a lightning producer in less than 30
minutes.
• Storms commonly travels at a speed of 40 km/hr or
more.
2.7 Lightning Can Strike “Out of the Blue”
Lightning can strike many kilometers from the parent
thunderstorm, well outside the rain area and even beyond
the visible thundercloud. Lightning can also strike from
debris clouds several tens of minutes after the parent
thunderstorm has decayed. Lightning strikes are arbitrary
and random and it has been recorded traveling from cloud
sources 60 km distant to cause injuries and
deaths. Lightning usually strikes at distances
between 4 and 10 km, but it commonly strikes at
distances of up to 15 km.
Anvil Cloud
Thunder always accompanies lightning: “sound and
light.” Hearing thunder indicates that that lightning was
within hearing range - 10 to 15km normally.
Thus, lightning safety requires a large standoff
distance from thunderstorms and a long standoff
time after apparent thunderstorm decay.
6-10 km
15 km
15 km
If you can hear thunder, you are within striking distance
Page 4 of 17
2.8 Lightning Strikes Anywhere
Lightning does not "decide" where it will strike until the
stepped leader descending from the cloud is about 30m
from the ground or object that is struck. Thus, short
objects in an open area can be struck by lightning even
if a tall object is nearby. If lightning strikes a nearby
object, shock can result either by direct contact or by a
side flash.
2.9 A Near-Miss Can Be Deadly
There are five mechanisms of lightning related injury and
death:
1. direct strike,
2. touch voltage,
3. side flash (or surface arc),
4. unconnected upward discharge, and
5. step voltage.
50,000
volts
m
If lightning strikes the ground, the high voltage gradients
cause currents to flow in concentrated channels on the
surface or within the soil, and can injure people nearby.
The associated step voltages and surface arcs,
respectively, can be deadly more than 40m from the
lightning strike point. In addition, there can be upward
discharges tens of meters in length from tall objects
(including people) that are located within tens of meters
from the strike point.
0 volts
30
About half of cloud-to-ground flashes form two or more
terminations when striking the earth. Lightning is known
to strike tall objects considerably below their tops. Many
lightning discharges are likely to produce electrical arcs
developing radially along the ground surface from the
strike point. In the context of lightning safety, a
conservative and prudent approach always is suggested.
STRIKE POINT
30,000 Amps
0.5m
Step Voltage
Current can flow through the body if the legs are
apart (step voltage)
.
Cows killed by step voltage
Page 5 of 17
2.10 The Effects Of Lightning
A lightning strike sends a strong electrical charge either through the body or over its surface. If it
hits you or something close to you, lightening can cause serious injury. You may get burned if
you have any metal on your body (a belt buckle, a zipper, or coins, for example). After a mild
lightning injury, you will usually feel better within hours or days. A severe injury, however, can
cause lasting damage to the brain, nerves, eyes, or ears, and may even be fatal.
2.10.1 Signs/Symptoms
In some cases, persons may be hit by lightening and not even know it. A mild strike may cause
pain, headache, confusion, tingling, numbness, or weakness, sometimes accompanied by
difficulties with vision, hearing, and memory. In a severe strike, the blast of electricity may tear
the clothing or shoes from your body. Burns may not be visible at first, but may appear hours
later. There may be broken bones, and if the heart is severely injured, it may stop.
2.10.2 Care
The victim does not carry any electrical charge. A severe lightning injury is an EMERGENCY.
The victim may need CPR if the heartbeat or breathing has stopped. Hospitalisation is needed
for tests and treatment. Even if the injury is mild, a doctor should be consulted. Some of the
symptoms may only manifest some time after the incident such as increasing pain, blurred
vision, trouble hearing, worsening headaches, numbness or tingling in the arms or legs,
increasing weakness and other symptoms.
3
3.1
LIGHTNING SAFETY
Policy and procedures
Thunder storms develop mostly on spring or summer days but can occur year round. There is a large
variation between regions in respect of the development of thunder storms and the frequency of
lightning strikes and they are sometimes difficult to predict.
The threats of lightning should be risk assessed and formal lightning safety procedures that are
appropriate for the region should be established.
Operations should prepare a Lightning Safety Plan and inform and train all personnel of its contents. In
principle, lightning safety is "anticipating a high-risk situation and moving to a low-risk location”.
All personnel who may potentially be exposed to the risks of lightning should be trained on lightning
safety and they should understand the company policy and safety procedures on the mitigation of risks
associated with inclement weather.
Essential components of any type of lightning safety system include:
1) A written lightning safety policy, together with a lightning safety plan;
2) Education about lightning and the organisation’s lightning safety plan;
3) Designation of a primary safety person (named designated weather watchers - persons who actively look for the signs
of threatening weather and notifies the chain of command if severe weather becomes dangerous);
4) Have a means of monitoring local weather warnings and forecasts;
5) Determination of when to suspend activities;
6) Established a chain of command that identifies who is to make the call to remove individuals from the field;
7) Designation of safe/not safe shelters for each venue;
8) Notification to persons at risk;
9) Planning for routing and evacuating people;
10) Determination of when to resume activities;
11) Carrying out of regular Lightning Action Plan drills;
12) Reviewing and modifying the Lightning Action Plan as needed.
All individuals have the right to leave a site in order to seek shelter if the person feels in danger
of impending lightning activity, without fear of repercussion or penalty.
Page 6 of 17
3.2
Decision Tree
."Lightning Safety Plans” should be site-specific, but they all share a common outline:
Policy and Lightning Safety Plan
3.3
Advance Warning
Evacuation
•Personal decision
•Weather forecasts
•Lightning detectors
•Chain of command
•Notification
•Safe shelters
Resume Activities
•Chain of command
Advance Warning of the Hazard
3.3.1 The 30/30 rule
During thunderstorms, no place outside is safe, but the risk can be minimised by assessing the
lightning threat and taking the appropriate actions. Attention should be given to early signs of
thunderstorms: high winds, dark clouds, rain, distant thunder or lightning. At this point, no new
task should be started that cannot be quickly stopped.
The 30second/30minute rule offers the best general lightning safety guidance where more
sophisticated technology for identifying the danger is not available.
It takes the sound of a thunderclap about three seconds to travel one kilometer while the lightning
flash is seen instantaneously. Therefore, for every three seconds between the flash of the
lightning and the bang of thunder, lightning is one kilometer away. A thirty second Flash-to-Bang
count means lightning is 10 kilometers away.
If the “Flash-to-Bang” count is 30 seconds or less, the thunder storm is close enough (10 km) to
be dangerous – seek shelter.
However, the 30/30 rule is often difficult to apply since it may be difficult (confusing) to associate a
specific flash with the roar. The distance that thunder could be heard is about 10 to 15 km. If one
cannot see the flash, or have difficulty to apply the 30/30 rule, just hearing the thunder is a good
backup.
The following phrases are useful reminders:
When Lightning Roars, Go Indoors!
If you can see it (lightning), flee it
If you can hear it (thunder), clear it.
Wait for at least 30 minutes until the last thunder is heard before leaving the shelter.
Use an “all clear” signal that is different from the “warning” signal.
3.3.2 Weather network information
Forecasts by TV weather channels, radio broadcasts and other networks may be useful sources
for predicting potential developments in the local weather for advance planning of activities.
All persons should be encouraged to become “weather wise” and to consider the risks of lightning
in the planning of their own activities. However, this should be the duty of the designated “weather
watchers”.
Page 7 of 17
3.3.3 Lightning detectors
Especially during the summertime, lightning activity can begin suddenly in areas of rain even if no
lightning or thunder has yet occurred.
Lightning detectors can give advance notice to shut down dangerous operations or to suspend
activities before the arrival of thunder storms. They also may signal "all clear" conditions after the
lightning threat has passed or if a storm might be passing at a safe distance.
Lightning detectors vary in complexity and cost, from large and expensive, dedicated equipment
packages to relatively inexpensive hand held units and they could detect lightning from about 60
kilometers to hundreds of kilometers. The technology applied (mostly the detection of
radio/electromagnetic waves emitted by lightning) and the intended use covers a wide range and
there are suitable systems available for a large variety of applications. Finding a detector and/or
signaling device that would suit site-specific requirements, easiest to use, and which offers the
most cost effective solution is a matter of risk assessment and surfing the internet, enquiring from
the market, etc.
However, beware of a false sense of confidence from detectors - none of them will detect all of the
lightning all of the time. None of them will provide "first bolt out of the blue" information or forecast
in advance the positions of lightning strikes on earth – they merely provide an unbiased indication
of the potential threat in line with the designed capabilities of the detector which generally exceeds
human perception.
An overview of lightning detection technology is given in Appendix 2.
3.4
Notification Of Affected Persons
Storms can grow from the small towering cumulus stage to a lightning producer in less than half an
hour. A chain of command should be established that identifies who is to make the call to remove
individuals from the field.
Designated weather watchers should be named - persons who actively looks for the signs of threatening
weather and notifies the chain of command if severe weather becomes dangerous.
If it will take a while to reach shelter (more than a few minutes) other arrangements should be made to
reach the safe place before lightning is an immediate threat.
In other instances, e.g. where potentially dangerous operations such as working with explosives is
involved, there may be duty-to-warn issues – in these circumstances the use of lightning detection
systems may be essential.
3.5
Evacuation To Safe Shelters
Having established the hazard, the other defenses for mitigating the hazard should be considered:
• Where is a safe refuge?
• How long will it take to get there?
• How long should persons stay there?
While nothing offers absolute safety from lightning, some actions can greatly reduce the risks. If a storm
is approaching, avoid being in, or near, high places, open fields, isolated trees, unprotected gazebos,
rain shelters, communications towers, flagpoles, light poles, metal fences, convertibles (back of a LDV
covered with canvas), and water.
A designated safe shelter for each venue should be identified during the planning stage and by use of
appropriate signage.
Some places are safer than others. Large enclosed structures are safer than smaller, or open,
structures. Avoiding lightning injury inside a building depends on whether the structure incorporates
lightning protection and its size. When inside during a thunderstorm, avoid using the telephone, taking a
shower, washing hands, doing dishes, or having contact with conductive surfaces, including metal
doors, window frames, wiring and plumbing. Generally, enclosed metal vehicles, with the windows rolled
up, provide good shelter from lightning.
An overview of safe and less safe shelters is given in Appendix 3.
More than 50 percent of lightning deaths occur after the storm has passed. This is because most people
do not realise that the lightning threat may persist for more than 30 minutes after the storm has moved on.
Page 8 of 17
4
REFERENCES
Following are some usefull internet sites regarding lightning safety:
http://www.lightningsafety.com/
http://www.stormwise.com/
http://www.viasala.com/
http://www.weathershop.com/boltek/
Page 9 of 17
APPENDIX 1: PERSONAL LIGHTNING SAFETY
The vast majority of lightning casualties can be easily, quickly, and cheaply avoided if the proper rules
are followed. People need to increase their awareness of lightning hazards, their knowledge of lightning
safety and the Company Safety Plan.
Step 1: Planning
Plan around the weather to avoid lightning hazards. Pay attention to the daily forecasts so that
one knows what to expect during the day. Also pay attention to early signs of thunderstorms. At
this point, do not start any new task that cannot be quickly stopped.
Lightning Warning Signs
In addition to the obvious warning of an ominously darkening sky, there are certain conditions that
can alert persons to a lightning danger before the strikes threaten. You are in a 'danger zone' and
need to seek immediate shelter if you experience any of the following:
• Raindrops or hail: Rain of any intensity (but more so with heavy rain) may signal the presence
of a thunderstorm cloud directly overhead, even if it has not yet produced any lightning or
thunder. Large, 'fat' raindrops are ominous, telltale signs of a towering cloud that has the
potential to produce a lightning strike at any second.
• Audible thunder or visible flashes: If you can see lightning or hear thunder at all, you are
within range of the next strike.
• Large, towering clouds: Cumulonimbus (thunder) clouds can develop rapidly overhead, even
among pleasant-looking skies; sometimes leaving no 'dark sky' appearance that often
otherwise precedes a thunderstorm. A growing cumulonimbus cloud's upper edges will usually
look hard and rounded, like cauliflower, as it protrudes skyward.
• Static on an AM radio: Distinctive crackling and popping sounds on an AM radio indicate that
lightning is occurring in your area.
• Lightning Detector Alarms: Several handheld lightning detectors are on the market that
sounds an alarm when lightning occurs within a set distance. These battery-operated detectors
are commonly used by personnel at golf courses, pools, parks and beaches. If your job or past
time involves large amounts of time outdoors, a portable lightning detector could be a good
investment.
Step 2: Establish the danger
Count the number of seconds from when the lightning flash is seen until the thunder is heard. If
that count is 30 seconds or less, you are in immediate danger. Stop what you’re doing and seek
safety in a substantial building and alert others in line with the Safety Plan.
Do not wait for the rain. Many people take shelter from the rain, but most people struck by
lightning were not in the rain. Where practicable go quickly inside a completely enclosed building,
not a carport, open garage or covered patio. If no enclosed building is convenient, get inside a
hard-topped all-metal vehicle. A vehicle with a solid metal roof and metal sides is a reasonable
second choice. Convertibles, cars with fiberglass or plastic shells, and open framed vehicles do
not count as lightning shelters.
MYTH:
Cars are safe because the rubber tyres insulate them from the ground.
TRUTH:
Cars are safe because of their metal shell.
Step 3: Inside the shelter
Inside the building, stay off corded phones, computers and other electrical equipment that put you
in direct contact with electricity or plumbing. Buy ground fault protectors for key equipment. Inside
a car, as with a building, avoid contact with conducting paths going outside, e.g. close the
windows, lean away from the door, put your hands on your lap, do not touch the steering wheel,
ignition, gear shifter, or radio.
Clouds don't have to be directly overhead for lightning to strike; it can arc out from the
thunderstorm for a distance of up to 15 km. Even when the sky looks blue and clear, be cautious.
If you hear thunder, remain in a safe shelter. Therefore, extreme caution should be practiced even
after a thunderstorm has passed.
Page 10 of 17
If Outdoors:
A lightning strike can seriously alter your life as you know it. In other words, go with your
best bet: Play it safe and do not be caught outdoors when lightning is around.
If caught outdoors, the focus on protecting yourself from lightning should not be on what type of
objects you are wearing, standing by, or carrying, but rather on avoiding the locations where
lightning can strike - which, essentially, is anywhere outdoors or in unprotected structures.
You are in equal danger of a lightning injury outdoors regardless of whether or not you are
standing near, carrying, or wearing any metal objects. Lightning is a force that is not influenced by
small objects on the ground, so distancing yourself from small metal objects will not make
you safe from lightning.- it remain a matter of chance whether lightning will strike near you or
not. Metal objects like umbrellas, golf clubs, bicycles and fences will attract a lightning channel
only if the strike is already a few feet away - in which case you would still experience an injury
from being that close to begin with.
It is commonly understood, for instance, that one should stay away from trees if outside during a
storm. There is some merit to that statement, but the truth is that there is still in danger from
lightning if you are outdoors at all. If you are caught outside, stay away from tall, isolated objects
like solitary trees, flagpoles, or posts. Remember that, contrary to the myth, lightning does not
always strike the tallest or largest object - it can strike anywhere. Also stay away from shorelines,
railroad tracks, and metal fences which could bring current from a 'far-away' lightning strike to you.
Although still not as safe as being indoors, dense woods provide a little protection due to the large
number of trees that decrease the chances of lightning strike to a tree next to you. However in
this, and any other case, do not stand close to any of the trees.
Jewelry, spiked shoes, watches or hair berets will do nothing to influence a lightning strike's
ground termination. However, if you are hit directly, lightning will usually flow through any metal
objects on your person, superheating (even vaporising) them and causing burns.
An imminent strike
A close or direct lightning strike will sometimes give you a short warning a few seconds before the
event, usually in the form of:
• A soft or loud buzzing, clicking, hissing or cracking sound.
• A tingling sensation
• Hairs on the arm or head standing on end
• Nearby metal objects emitting a soft, blue-white glow called ‘St Elmo’s Fire’.
These signs indicate a direct strike may occur within seconds. In most cases, you will not have
time to react. However, if you are unable to reach shelter and you experience any of these signs,
or if you otherwise feel that you are in immediate danger, assume the following position quickly:
Move your feet close together, crouch down, and grab your ankles. Tuck your head down as far as
you can. Do not lie flat on the ground. If there is a group of people they should spread out and not
bundle together.
Remember, this is a desperate last resort; you are much safer if you follow the previous steps and
avoided this high-risk situation. Crouching merely reduces the risk of step voltage and arcs.
Lightning strike victims:
Victims of lightning strikes are not always initially in a fatal situation. Typically a lightning strike will
cause cardiac and/or respiratory arrest that can be corrected by proper resuscitation (CPR). Many
lightning-related deaths occur when the victim does not receive the proper medical attention. If
you witness a lightning strike incident;
1. Survey the scene for safety.
2. Activate the local Emergency Response System.
3. Note that lightning victims do not “carry a charge” and are safe to touch.
4. If necessary, move the victim with care to a safer location.
5. Evaluate airway, breathing, and circulation, and begin CPR if necessary.
6. Evaluate and treat for hypothermia, shock, fractures, and/or burns.
Page 11 of 17
APPENDIX 2: AN OVERVIEW OF LIGHTNING DETECTION EQUIPMENT
Lightning hazards can be mitigated by advanced planning. One part of the lightning safety program
should include an early detection and warning alarm package. Lightning detectors vary in complexity
and cost from expensive, large dedicated equipment packages to relatively inexpensive handheld
models.
Available technologies of the present day lightning detectors include:
1. Radio Frequency (RF) Detectors. These measure energy discharges from lightning. They can
determine the approximate distance and direction of the threat.
2. Inferometers. These are multi-station devices, much more costly than RF detectors and they
measure lightning strike data more precisely. Usually they require a skilled operator.
3. Network Systems. National lightning detection networks are available in some countries where
lightning strikes are reported to a central station. Local storm data is available and past strike
information could be used for risk assessment purposes.
4. Electric Field Mills. These pre-lightning equipments measure the potential gradient (voltage)
changes of the earth's electric field and report changes as thresholds build to lightning
breakdown values.
5. Optical Monitors. These can provide earlier warning as they also detect cloud-to-cloud lightning
that typically precedes cloud-to-ground lightning.
6. Hybrid Designs. These monitors use a combination of the other single-technology designs. Two
or more sources of information (for example, cloud-to- cloud, cloud-to-ground, optical
recognition, EFMs) may be better than just one.
Lightning Detection Options – Accuracy vs Cost vs Complexity
Source of Information
Accuracy
Cost
Complexity Level
Hearing thunder
Danger is near
None
Simple
TV weather channel
General information
None
Simple
Small handheld
General information
From $70
Simple
Handheld detectors
50-60% accurate
$200 to $700
Simple to Somewhat
Boltek portable system
70-80% accurate
Up to $1,500
Somewhat
WXLine base unit system
90-95% accurate
Up to $7,000
Somewhat
Beware of a false sense of confidence from detectors; none of them will detect all of the lightning all of
the time. None of them will provide "first strike/bolt out of the blue" information or forecast in advance
the positions of lightning strikes on earth.
The Radio Frequency (electromagnetic) detectors are used most widely. These detector receiver
algorithms operate at different frequencies and wavelengths. The operating range of the different
models could fall within an overall range between 10kHz and 120 MHz, depending on the application.
Detectors can display early warning of lightning conditions to hazardous operations. Some detectors
can start/stop standby power generators. A signaling or alarm notification method is essential to alert
field personnel of developing dangerous circumstances. Two-way radios, remote activation siren
packages, strobe lights, and other methods are available.
Finding a detector and/or signaling device that would suit site-specific requirements, easiest to use, and
which offers the most cost effective solution is a matter of risk assessment and surfing the internet,
enquiring from the market, etc.
Page 12 of 17
1. Examples of some of the systems available on the market.
Hand held StrikeAlert ≈ $70
Hand held ScyScan ≈ $ 250
Hand held Bolteck Thunderbolt ≈ $650
Fixed installation Lightning Alert ≈ $200
Portable Boltek LD 250 system with mapping
software ≈ $1,000+
Fixed installation Wxline hybrid system with
software ≈ $7,000+
Example of Boltek software
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2. Features of lightning detectors.
When selecting lightning detection systems, the application and reliability (of detecting lightning,
durability, batteries, usability) are the most important considerations.
Other features of lightning detectors that could be considered, depending on site specific needs,
include:
• TEXT SCREEN DISPLAY vs LED
• USER SELECTABLE MENU OPTIONS
• LIGHTNING DETECTION RANGE INDICATOR
• THUNDERSTORM CELL TRACKING
• STORM IS LOCAL DISPLAY
• TIME TO CLEAR DISPLAY
• USER SELECTABLE BACKGROUND NOISE ROUTINES
• USER SELECTABLE ALARM DISTANCE
• SEVERE STORM WARNING
• SECOND ALARM RANGE OPTION
• SQUALL LINE WARNING
• HIGH/NORMAL STORM DETECTION SENSITIVITY
• MULTIPLE STORM CELL WARNING
• IDENTIFY CLOSEST STORM CELL
• WARNING MODES
• STORM DISTANCE DISPLAY
• EXTERNAL SPEAKER JACK
• STORM APPROACHING DISPLAY
• STORM APPROACH SPEED DISPLAY
• ESTIMATED TIME OF ARRIVAL DISPLAY
• POWER SUPPLY OPTIONS
• WATER RESISTANT
• SOFTWARE AND UPGRADES
• LOCAL SUPPLIER AND TECHNICAL SUPPORT
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APPENDIX 3: GOOD LIGHTNING SHELTERS FOR OUTDOOR WORKERS
1. Summary
Sudden thunderstorms may bring urgency for outdoor workers to cease work and quickly relocate to
refuge. Ordinary wood buildings provided for worker comfort, lunch breaks or safety from rain or sun are
not safe from lightning. “Safe” and “not safe” structures and their placement on typical properties are
discussed, together with some examples of suitable shelters.
2. Behavior of lightning on struck objects
High-frequency current flowing on a metal conductor generates an electromagnetic field. One effect of
this is to confine electrical flow towards the outside of it. This is called “skin effect.” The thickness of the
layer of restricted penetration is called “skin depth.” Skin depth is proportional to the square root of the
inverse of the frequency. The higher the lightning frequency, the smaller the depth.
People react much differently to lightning than do metal objects. The human body, being some 65% salt
and water, is a good conductor. Direct lightning strikes can follow either through internal or external
pathways or both. Indirect lightning damage mechanisms include:
1)
flashover from an intended conductor (for example, a gazebo or tree) to an unintended conductor
(such as a person seeking refuge from rain or hail);
2)
step and touch voltages where a person’s hands or feet intercept electrical differentials, which then
seek to equalise via the body; and
3)
interrupting the normal electrical heart beats leading to arrhythmia.
3. Safe and not safe structures
Small open shelters are common on athletic fields, golf courses, parks, roadside picnic areas,
schoolyards, and elsewhere. Many of these shelters are built to protect against rain or sun, not lightning.
What can be done to minimise risk/maximise safety for people inside them under direct and indirect
lightning strike conditions? Although there is no such thing as a lightning-proof small outdoor shelter, a
properly designed and installed lightning protection system may make a difference. Sometimes the
difference is between life and death.
A basic lightning protection system (LPS) against direct strikes to an ordinary structure includes:
1) air terminals,
2) down conductors, and
3) ground terminals.
These three elements of the LPS must form a continuous conductive path (actually at least two paths)
for lightning current, with all connections between the elements typically being accomplished by bolting
or welding. The function of the LPS is to intercept lightning and safely direct its current to ground and to
intercept electric arcs developing along or under the ground surface toward the shelter from lightning
strikes.
Various standards on LPS are available for reference, e.g. the European Standard BS EN 62305, the
Institute of Electrical Electronics Engineers IEEE std 80, etc.
4. Shelters Unprotected from Lightning
In the absence of the three-element lightning protection system described above, the structure should
be considered unprotected from lightning. Small shelters with or without lightning protection should be
avoided where possible during thunderstorms.
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5. Protected Shelters
A small shelter equipped with a properly designed and installed LPS may provide reasonable protection
from direct lightning. It is essential, however, that a person inside the shelter does not touch any
element of the LPS and tries to position himself or herself at approximately the same distance from all
down conductors. Electrical signs, pop machines, water faucets, irrigation controllers, etc. can increase
personal hazards inside the shelter should lightning strike nearby. A small shelter, even one protected
as described here, should be viewed as the last resort option. Refuges with much higher safety levels
such as large buildings and fully enclosed metal vehicles should be sought instead when time permits.
A small recreation shelter with peaked roof should have an overhead shield wire system or Franklin rod
system. Again, there are reference standards available for the installation of adequate LPS for these
type of structures.
Knowing the above described behaviour of lightning upon, say, an automobile, it is apparent that a fully
enclosed metal vehicle is also a safe shelter. Other all-metal mobile equipment such as airplanes,
buses, vans, and construction equipment with enclosed mostly-metal cabs are also safe. These are
examples of an everyday “Faraday Cage” where the charge and current is confined to the outside metal
layers.
It should be emphasised, however, that the “outer metal shield” should not be compromised. This
means that:
1)
2)
3)
Windows need to be rolled up.
Person must not make any interior contact with external objects, such as radio dials, metal door
handles, two-way radio microphones, etc.
Person should avoid all other objects that penetrate from inside to outside.
Unsafe vehicles include those made of fiberglass and other plastics, plus small riding machinery or
vehicles without enclosed canopies, such as motorcycles, farm tractors without fully enclose cabin, golf
cars, and the load trays of LDVs that are open or covered with canvas or with a fiberglass canopy.
Metal buildings are safe places. So, too, are large permanent structures made of masonry and of wood.
Again, the caveat is not to become a part of the pathway conducting lightning. This means avoiding all
electrical circuits, switches, powered equipment, metal doors and windows, hand rails, and so on. Small
post-supported structures, such as bus stops or picnic shelters, are not safe and cannot be made safe
for people.
Metal shipping containers, for example, can be easily modified to become cheap, effective, portable,
and rapidly deployable shelters – note other safety and health requirements are also applicable.
6. Shelter placement on properties
Each site location is unique and different and shelters should be located where the probability of
lightning strikes might be lower. That is, in relatively low areas, preferably surrounded by a large number
of trees of approximately the same height. They should not be located on hilltops, near metallic fences,
power poles, tall trees, or near water.
However, they should also be within reach from the working areas. It is generally proposed that 3 to 4
minutes, even under rapid evacuation, should be adequate for reaching safety if supported by
appropriate warning systems.
Following are some examples of decisions to be made when seeking shelter:
1) Is there a pickup truck nearby that one can get to faster than an alternative shelter?
2) If there is a choice between a metal shelter and a plastic/wooden shelter at equivalent distances,
choose the metal shelter.
3) If the only nearby structure is locked, seek an overhanging roof, where possible.
4) If one is caught with no shelter of any type nearby, crouch to the lowest possible position, avoiding all
nearby metal objects.
An incident report should be filed in the event of 3 and 4 above if it occurred during real or simulated conditions
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7. Conclusion
To attain 100% lightning safety is not possible. But pre-planned defenses can assure a best attempt to
achieve high levels of safety. Hear thunder? When to stop activities? Hear more thunder? Get ready to
evacuate to safe shelter. What is a safe place? How long to stay inside the shelter? These and other
questions must be answered well in advance of the thunderstorm evacuation emergency.
Examples of shelters for Lightning Protection
(source: http://www.lightningsafety.com/nlsi_pls/outdoor_worker_shelters.html)
Good
Poor
Features of poor shelters
•Metal roof (air terminal)
•Wooden structure (no down conductor)
•Poor earthing
•Conducting rails
•Metal roof (air terminal)
•Wooden structure (no down conductor)
•Poor earthing
•Canvas provide no protection
•Cab of LDV provide better protection
•Metal roof (air terminal)
•Wooden structure (no down conductor)
•Poor earthing
•Metal roof (air terminal)
•Open sides – no protection
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