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Outdoor Lightning Protection and Safety
by Alan Sheehan B.E.
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by Alan Sheehan B.E.
Each year in Australia lightning claims up to 10 lives and causes over 100 injuries. Up to 80 of those injuries happen when people use telephones during thunderstorms and receive an electric shock, hearing damage, or burns when lightning strikes telephone wires in their area. This is obviously the largest source of lightning related injuries in Australia. Irrespective of this, when outdoors there is still great value in knowing what to do if caught in a thunderstorm to minimise the risk of being struck.
The first long term warning signs are obviously the build up of storm clouds. This may be evident several hours prior to arrival of the thunderstorm, so it is worthwhile being aware of the surrounding weather to avoid being in a high risk location when the storm arrives.
The short term warning signs are, of course, the familiar sights and sounds of lightning and thunder. The time difference between the lightning flash and the sound of the thunder can be used to estimate the distance to the lightning strike/storm. When there is a 10 second gap between the lightning and the thunder, the lightning is about 3 kilometres away - so at 3 seconds it is about 1 kilometre away. When the time difference is less than 10 seconds (lightning less then 3 kilometres away) it is time to seek shelter urgently!
The immediate warning signs which may precede a lightning strike are:
Lightning (ground strike) occurs when the charge of static electricity in the clouds builds up to the point where there is enough voltage for a spark to jump the gap from cloud to earth. The charge in the cloud will be opposite to the corresponding charge induced on the ground. These opposite charges are attracted, and will try to cancel each other out through the lightning strike. High points, spikes and conductors will each affect the electric field, usually concentrating it. This means that tall, pointy or conductive objects are more likely to be struck by lightning than other objects.
Just before a lightning strike, the voltage (potential difference) between the cloud and the ground can be several million volts! The charge on the cloud and on the ground is dispersed over a relatively large area.
When the lightning strikes, the lightning bolt is actually a track of ionised molecules in the air. The average lightning bolt carries a current of 10,000 to 30,000 amps! (for only a very short time!). All this current must move from being dispersed over the ground (or cloud) to/from the lightning bolt, so large currents and voltages occur in the ground. The voltage is very high near the strike, and low away from it. This causes "step potential".
Step potential means that if someone touches the ground at two points, one closer to the lightning strike than the other, an electric current will flow through them. The closer the lightning strike (or the wider the step between the 2 points) the higher the step potential, the higher the current, and the more serious the injuries.
So even if not directly hit by lightning, just being close by can result in electrocution if steps are not taken to avoid the step potential.
Seek shelter in a "hard top" vehicle or solid building. These provide protection by conducting the lightning to earth around you.
Avoid small structures or fabric tents. These lack sufficient mass to conduct a lightning strike safely around you, and depending on the method of construction may attract lightning.
Never shelter under a single tree or a small group of trees. As the highest point in that area, the tree is likely to be struck. Being near the tree increases the risk of step potential.
If far from shelter, crouch alone with feet together, preferably in a hollow. This will keep you as low as possible without creating a step potential risk. Remove metal objects from your head and body. Don't lie down (step potential) and avoid being the highest object.
Don't fly kites or model aeroplanes with control wires.
Don't handle fishing rods, umbrellas or golf clubs, etc.
Stay away from metal poles, fences, clothes lines, etc.
Don't ride horses, cycles or drive in open vehicles.
If driving, slow down or park away from trees, power lines, etc. Stay inside metal-bodied (hard top) vehicles or caravans but don't touch any metal sections.
If swimming, surfing, etc leave the water immediately.
If boating, go ashore to shelter as soon as possible. A bridge or high jetty may offer immediate protection.
Be sure the mast and stays of a sailing boat are adequately "grounded" to the water.
Apply immediate Expired Air Resuscitation (EAR) if not breathing, or immediate Cardiopulmonary Resuscitation (CPR) if no pulse. Continue this until medical help arrives and they will have a good chance of survival. (You will not receive a shock from the victim.)
When struck, people do not glow or "fry to a crisp", but the heart and breathing are often affected.
Only about 30% of people struck actually die, and the incidence of long term disability is low, particularly when first aid is applied promptly.
If your clothes are wet, you are less likely to be seriously injured if struck, as most of the charge will conduct through the wet clothes rather than your body.
Lightning can and does strike in the same place more than once!
Worldwide, thunderstorms are producing approximately 6,000 lightning strikes every minute!
Lightning Protection Action Guide, by Emergency Management Australia, available from your local State or Territory Emergency Service Unit.
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