Extreme Events
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Lightning
Lightning southwest of Brandon, MB. Summer 2000. Photo: Dan Lewis (Black Tree Photography)
Lightning is an electrical discharge caused when static electricity builds
up between thunderclouds, or thunderclouds and the ground. Lightning strokes
carry up to 100 million volts of electricity and leap from cloud to cloud,
or cloud to ground and vice versa. Lightning tends to strike higher ground
and prominent objects, especially good conductors of electricity such
as metal.
Thunder is the noise caused by the explosive expansion of air due to
the heat generated by a lightning discharge. Thunder may have a sharp
cracking sound when lightning is close by, compared to a rumbling noise
produced by more distant strokes.
Because light travels at a faster speed than sound, you can see a lightning
bolt before the sound of thunder reaches you.
To judge how close lightning is, count the seconds between the flash
and the thunder clap. Each second represents about 300 metres. If you
can count less than 30 seconds between the lightning strike and the thunder,
the storm is less than 10 km away and there is an 80 percent chance
the next strike will happen within that 10 km. If you count less
than 30 seconds, take shelter, preferably in a house or all-metal automobile
(not a convertible top) or in a low-lying area.
Lightning may strike several kilometres away from the parent cloud and
precautions should be taken even if the thunderstorm is not directly overhead.
Learn the 30-30 rule
- Take appropriate shelter when you can count 30 seconds or less between
lightning and thunder.
- Remain sheltered for 30 minutes after the last thunder.
If caught outdoors:
- Keep a safe distance from tall objects, such as
trees, hilltops, and telephone poles.
- Avoid projecting above the surrounding landscape.
Seek shelter in low-lying areas such as valleys, ditches and depressions
but be aware of flooding.
- Stay away from water. Don't go boating or swimming
if a storm threatens and land as quickly as possible if you are on the
water. Lightning can strike the water and travel some distance from
its point of contact. Don't stand in puddles even if you are wearing
rubber boots.
- Stay away from objects that conduct electricity ,
such as tractors, golf carts, golf clubs, metal fences, motorcycles,
lawnmowers and bicycles.
- Avoid being the highest point in an open area. Swinging
a golf club or holding an umbrella or fishing rod can make you the tallest
object and a target for lightning. Take off shoes with metal cleats.
- You are safe inside a car during lightning , but
don't park near or under trees or other tall objects which may topple
over during a storm. Be aware of downed power lines which may be touching
your car. You are safe inside the car, but you may receive a shock if
you step outside.
- In a forest , seek shelter in a low-lying area under
a thick growth of small trees or bushes.
- Keep alert for flash floods , sometimes caused by
heavy rainfall, if seeking shelter in a ditch or low-lying area.
- If caught in a level field far from shelter and
you feel your hair stand on end, lightning may be about to hit you.
Kneel on the ground immediately, with feet together, place your hands
on your knees and bend forward. Don't lie flat.
- If you are in a group in the open , spread out, keeping
people several yards apart.
Indoor Precautions:
- Before the storm hits , disconnect electrical appliances
including radios and television sets. Do not touch them during the storm.
- Don't go outside unless absolutely necessary.
- Keep away from doors, windows, fireplaces , and
anything that will conduct electricity, such as radiators, stoves, sinks,
and metal pipes. Keep as many walls as possible between you and the
outside.
- Don't handle electrical equipment or telephones.
Use battery operated appliances only.
Note: Persons who have been struck by lightning receive
an electrical shock but do not carry an electrical charge and can be safely
handled. Victims may be suffering from burns or shock and should receive
medical attention immediately. If breathing has stopped, mouth-to-mouth
resuscitation should be administered. If breathing and pulse are absent,
cardio-pulmonary resuscitation is required. |