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Paper
prepared by Voyageur Outwrd Bound School
Lightning
It is estimated that lightning kills approximately 150-300 people
annually in the United States, more than any other natural disaster,
including floods, earthquakes, blizzards, tornadoes, and hurricanes.
The highest concentration of lightning injuries occur in high mountainous
areas and on large bodies of water with the majority of victims
being people who are outdoors for recreational purposes.
Violent lightning storms can occur very frequently in most of VOBS
course areas. It is one of the most unpredictable, objective hazards
a group may encounter. It is extremely important to educate and
monitor ourselves and our students in the hazards of lightning and
the precautions we must take to minimize risk.
Physics of thunder and lighting
Thunderstorms are the product of violent air updrafts caused when
warm and cold air masses collide. Warm, moist air gets thrown aloft
into the cold heights, building into a thunder head. The air currents
within the thunder head are so gusty that the raindrops are repeatedly
broken into smaller drops. Each time this occurs, the negative hydrogen
electrons are separated from the positive water droplets. The violent
updrafts move the negative charges upward, slowly overcharging the
top of the cloud.
After a while, enormous charge differences accumulate. Air, normally
a good insulator (poor conductor), will break down or ionize in
the face of these differences. Once the air is ionized, it will
discharge the electrical differences quickly. The discharge creates
a great flash of the negative electrons returning to the positive
charges. This movement of electrons makes light and heat. The light
we see as the flash of lightning. The heat we hear as thunder. The
movement of electrons heats the air to tremendously high temperatures.
This heat momentarily expands the air. Milliseconds later, the cooler
surrounding air crashes back into the Atunnel@ created by the hot
flash. This noisy expansion and compression we call thunder.
Hazards
The primary dangers of cloud to earth discharges are direct hit
and ground current. Your aim is to avoid both.
Direct hits
Lightning usually strikes the highest points in an area. Avoid being
the highest object or standing on or near the highest object. On
open water or high plateaus, that object may be your head. On flat
forested land where trees tend to be of similar height, it can hit
any where, but it is more likely to hit high points such as the
tallest tree, a high knoll, or a cliff.
Ground currents:
The current in a lightning bolt does not dissipate at the point
of the direct hit. The charge flows along the easiest paths of electrical
conduction on the earth=s surface such as wet rock, tree root systems,
water-filled cracks or crevices, natural fissures or chimneys, and
wet ropes. High voltage current may also take the shortest path
to the ground, jumping the gap between an overhang and the ground.
This is known as the Aspark gap.@
Physiological aspects of a lightning strike
Electrical currents passing through the body may cause burns, muscle
spasms, heart stoppage or fibrillation, brain malfunction and cessation
of breathing. The extent of injury depends on the amplitude and
duration of the current and the path of flow through the body. When
a person is struck directly, the current is apt to be so large that
the results are fatal, no matter what the path of flow through the
body. Ground currents are weaker hence the particular current path
through the body makes a significant difference. For example, current
passed from hand to hand will travel through the heart, spinal cord
and vital organs, yet the same current from foot to knee of the
same leg is not as potentially damaging.
1. Instruct and monitor students to follow precautions necessary
to avoid direct hits and ground currents associated with lightning.
Students are not to travel independently until they have demonstrated
the ability to follow these precautions.
2. When storms are in the area, actively assess route and activity
in relation to the time it will take to get to a relatively safe
location. Move to an area where escape from dangerous locations
in a timely manner is possible (paddle close to shore, prepare to
evacuate off ropes courses, bail off peak ascents, travel close
to easy bail-out points when above treeline, etc.)
3. When it is determined that a storm is approaching, get to safe
ground before the interval between the lightning and thunder reaches
15 seconds (get off the water, get down off high, exposed plateaus,
off ropes courses).
4. When the interval between the lightning and the thunder is 15
seconds or fewer, begin a lightning drill (see guidelines). Remain
in drill until the interval is more than 15 seconds away.
5. When the storm has moved more than 15 seconds away, stay within
a relatively safe area where a repeat drill could be conducted in
a timely manner if necessary. After the storm has completely passed,
continue travel in an area where escape from dangerous locations
in a timely manner is possible until storms are no longer in the
area.
Guidelines
A. Precautions:
1. In mountain environments plan ridge walks and peak ascents with
an early enough start to reach an unexposed area by early afternoon.
In general, it is unwise to travel extensively on high exposed terrain
during the afternoon. In water environments, you may need to opt
out of doing a major big lake crossing if storms are in the area.
2. Be aware of weather patterns and approaching storms. Actively
monitor the distance of approaching storms. Sound travels at about
1100 feet per second, so the sound of thunder travels about one
mile in five seconds.
B. Seeking an ideal location for a lightning drill:
1. If exposed to possible direct strikes, take advantage of likely
strike points. Lightning will tend to hit a tree, pinnacle, or other
high point rather than the person near it if the object is five
to 10 times or more the height of the person and the horizontal
distance from the person to the tree is about half the object=s
height. Locate yourself within this Acone of protection.@
2. When amongst many trees of similar height, location such a way
as to be equidistant between two trees. Avoid the tallest trees.
3. Avoid being a bridge between an object and the ground. For example,
do not lean against tent poles, trees or vehicles.
4. Avoid potential paths of conduction such as wet, lichen-covered
rocks, cracks and crevices (wet or dry), areas subject to the Aspark
gap@ such as overhangs and mouths of caves, wet ropes, tree roots.
C. Lightning drillCAt the first count of 15 or less:
1. Spread out to reduce the possibility of one strike affecting
more than one person, but keep everyone within visual and auditory
distance of an instructor.
2. Get in an ideal location relative to your immediate surroundings
(within cone of protection, equidistant between trees, not in spark
gap zone, off large tree rots, etc.).
3. Remove metal objects and keep them away from body contact as
they can cause serious burns if exposed to current.
4. Prepare and monitor for the potential of hypothermia by utilizing
necessary rain gear, insulating clothing, and snacks.
5. If the lightning gets much closer, or you hear or feel static
electricity, assume a lightning drill body position. Using available
insulation to protect from ground current, span as small a distance
(occupy as little area) as possible. Crouch, keeping feet together
and hands off the ground.
D. Considerations:
1. If it is necessary to choose, continue travel into a safer area
rather than do a lightning drill in an area with high risk of strike
(continue to move down off a ridge, paddle out of open water to
the shelter of trees along the shoreline).
2. If in a swamp where it is difficult to get to dry land, it is
better to be sitting in aluminum boats than standing in water. Stay
in boats and seek shelter among low-lying shrubs. Try not to position
yourself too close to trees. Instructors should be in separate boats,
spread out, yet within easy range of communication. With aluminum
canoes, insulate yourself from the boat if possible.
3. Under ideal circumstances, when a group of individuals is under
the protection of a tarp or tent, a decision may need to be made
whether or not a group should get out of the dry environment and
spread out, or whether to stay put. The tent or tarp must be in
a protected, ideal location. In addition, severity of the storm,
exposure to wind and possible blow-downs of limbs and trees, and
level of difficulty in managing a spread-out group in the dark should
all be considered.
4. Once a lightning path is determined, there is a high probability
of multiple strikes.
E. Treatment for a lightning strike:
1. Give AR and CPR as needed as well as treat other wounds. Take
precautions to avoid exposure to bodily fluids.
2. Evacuate if a victim of a lightning strike exhibits any of the
following:
a) burns
b) cessation of breathing
c) cardiac arrest
d) change in level of consciousness
e) change in behaviour
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