AVOIDING SHOCKS WHEN GETTING OUT OF CARS
John Chubb ? John Chubb Instrumentation
I have received many emails commenting on experience of shocks when people get out of their cars. I hope the following comments will help by suggesting what can be done directly to minimise problems and giving hope for the future.
The experience of getting a shock on getting out of a car is primarily because it is the person that becomes electrostatically charged on rising from the seat surface. It is not because the car is charged. (It may be that newer tyre materials using silica will allow significant charging of the car, but that is more for the future). Studies we have done show that high body voltages can arise even when wearing natural fibre clothing (for example, cotton or wool) and even when the ambient humidity is up around 50% RH. The problem may be worse with certain clothing and with the reduced humidities created by air conditioning systems.
If you experience shocks then what can you do to avoid them? I hope one or more of the following suggestions will prove helpful:
1) Get out of the car more slowly ? twist to face out of the car, then rise
2) keep contact with the car bodywork as you get out of the car
3) have a piece of leather or wood in your hand and touch the car body, or a nearby ?earthy? item, with this for a second or two
Do NOT get out of the car quickly and move to a latched-on petrol filler nozzle and touch this before touching earth to remove charge from the body. If your body voltage is high enough to give you quite a shock (over 10,000V) then the spark on touching the filler nozzle might ignite any flammable vapour issuing from the tank during filling.
Work is continuing to find seat surface materials that will avoid the chance of significant voltages arising on the person rising from the seat to leave a car. This is primarily a question of seating material, because it is not practical to consider requiring special clothing to be worn! The choice of suitable material is, of course, constrained by many practical features ? quite apart from those relevant to static electricity. Progress has been made towards ways to limit body voltages with test materials, but there is some way to go before practical seat materials can be approved and become available.
24 July, 2002