Botswana Insurance Company Botswana insurance company
 
How to reduce the risk of lightning strikes
Tip 1.
  1. The safest place you can be if outdoors and there is a lightning storm, is inside a car with the doors closed because if the car is struck, the lightning  path, is around the metal surface, (this is called a Faraday cage), through the tyres to earth.
  2. If in the open crouch down with your feet together, and be at least an arm's length (approx 1, 5 metres) away from the next person.    Do not lie, or sit on the ground, or lie against a fence with your feet on the ground.
  3. Do not shelter under an umbrella in the open, especially in a group.
  4. If there is a single tree close by, then it is better to get under the branches, but stay as far away from the trunk and overhanging branches as possible (at least 1,5 metres), and crouch down as mentioned above. 
  5. If you are on a mountain, seek shelter well inside a cave, or adopt the crouch position.
  6. Don't shelter inside a tent, it can be extremely dangerous as a lot of tents have either alluminium or carbon fibre poles, which when    erected will give off a stream of "Positive Ions"; this is an attraction to lightning. If lightning does strike the tent, then there is a very high possibility that it will then "jump over" to anyone lying in the tent.
  7. Classic examples of "Step voltage" are when animals are killed en-mass 
  8. Suspend outdoor activities if thunder is less than eight seconds after a lightning flash.
  9. Take immediate cover if the thunder is 3 or less seconds as it means the storm centre is within 1 Km.
Tip 2.
In rural areas, I believe the majority of fatalities are caused in the following way.

  1. When a storm is approaching people will tend to gather under cover in a group, probably in a "traditional home".
  2. There will probably be a fire place in the centre of the room with smoke drifting up through the apex of the thatched roof.
  3. The people will probably congregate around the fire in fairly close proximity to one another, some even holding onto others, e.g. parents and children, to give comfort etc.
  4. At this point, the smoke from the fire will be releasing a stream of "positive Ions" into the atmosphere, which will attract the "negative Ions" from the clouds. When these "Ions" meet, then a path is completed, allowing the main arc of electricity to form.
  5. What we then see, are flashes (up to about 8 of them) of electricity flowing from the clouds to the earth and vice versa.
  6. When the arc hits the apex of the house, it will take for the easiest way to earth, either via the building walls, and/or anything within the building (human or objects) that it can "jump across to, from the roof". A human struck in this way would very likely show signs of burns at the entry and exit points, and, probably under the arms and in the groin area.
  7. A major part of the arc would travel down the "Ion smoke trail" strike the floor and dissipate into the earth. This huge rush of current from the arc then dissipates across the floor in a similar manner to a stone being thrown into a pond. The area closest to the strike is the most hazardous, and if  people are standing with their feet apart, (which is the natural way) then, the potential across their limbs may be sufficient to cause heart failure.
  8. The final problem could be that when the arc hits the fire causing everything to catch alight.
Tip 3.
Simple precautions one can take.

  1. Apart from the tips given above, the next step is to try and provide some protection for the house. To do this it is necessary to "construct a Faraday cage"
  2. A Faraday cage is a structure that will shield anything inside of it from electrical discharges, e.g. lightning, or high voltage flashovers. As mentioned above, a motor car is an ideal Faraday cage.
  3. To apply this to a house a simple Faraday cage can be made by using fencing/baling wire.
  4. If we consider a rondaval type building, the wire needs to be laid across the building from East to West and preferably from North to South. (It does not have to follow the N.S.E.W co-ordinates; this is only to illustrate the form it should take).
  5. The wire needs to lie on the outside and follow the contour of the building from ground level, across the top and back down to ground.
  6. At each point where the wire touches the earth, a trench needs to be dug, about 800 to 1000 mm deep and about 3 to 5 metres long, (the deeper the better as it lessens the effect of step voltage). The wire must continue into the length of the trench, the soil put back and compacted down tightly over the wire.
  7. The wires should be tied together at the apex of the building.
  8. What this effectively does is to create a "relatively low conductive path" to the lightning arc, as it will always take the easiest path to earth.
  9. Whilst this solution is by no means the ideal, it will divert a large amount of energy away but you may still experience the reduced effects of the strike, but they should survive.
  10. If people are sheltering inside the house, they should extinguish any fire, preferably sit on a chair or bed with their feet off the ground, and keep as far apart from one another as possible.
  11. There are other methods of protection like having a lightning conductor (as seen next to thatched houses), or two high poles on either end of a building with a wire strung between them, which is buried in a trench or fixed to rods driven into the ground.
  12. The choice of materials is a major cost factor.In industry or commerce, copper wire, combined with rods or earth mats would be used.

The above is a précised article written by Frank Calbourn who has been in the South.African Sugar industry for 30 years and lightning problems were part of his specialization. He has presented three technical papers on the subject, one paper being reproduced in an International Sugar journal.