Static Electricity at the Gas Pump

Auburn, Nov. 11, 2003 --- Have you noticed the signs on gas pumps about the dangers of static electricity while refueling your car? These warnings are not a gimmick. Static electricity can spark a fire or explosion so consumers need to be careful and heed the warnings.

Static electricity is an electric charge caused by an imbalance of electrons on the surface of a material. It is most commonly caused by the contact and separation of materials. The area of contact, the speed of the separation, relative humidity and other factors determine the amount of charge created. One example of this is a person walking across a carpeted floor. Static electricity is generated as the shoe soles contact and separate from the carpet.

“Static electricity can build up when a person exits and re-enters a vehicle, particularly in cool or cold and dry conditions,” said Dr. Jesse LaPrade, an Extension environmental specialist.

“When you exit and re-enter your vehicle while refueling, there is the potential for sufficient static electricity to build up that a spark can discharge between your body and the fuel nozzle. In rare circumstances, the spark can ignite gasoline vapors around the fill spout, causing a brief flash fire,“ LaPrade said.

Once vapors ignite, the fire will continue until the fuel supply is shut off. In most cases, damage and injuries are minor, but serious personal injury and major property damage may occur when the fuel supply from the dispenser is not stopped.

In most cases, when people pull into a gas station to refuel a vehicle, they open the car door, slide out of the seat, open the fuel pipe cover of the vehicle, touch the nozzle on the gas pump, and perhaps touch the pump to use a credit card--all before they insert the nozzle into the fill pipe. Any static charge that was picked up in the car is dissipated several times.

A new static charge can be picked up if you get back into the car after the refueling has started. The synthetic material of the car seats and clothing add to the possibility of picking up a static charge. If you don’t touch metal before returning to the nozzle and fuel pipe, that static charge can be transferred when you touch the nozzle, thus creating the potential for a flash fire.

According to the Petroleum Equipment Institute there are three causes of static electricity fires at gas pumps:

50 percent are caused when a person returns to a vehicle during refueling and doesn’t shut the door or touch other metal when leaving the car to remove gas pump nozzle from the car’s fuel pipe.
29 percent are caused when a person unscrews the gas cap.
21 percent occur for other reasons.

There are several theories about why static fires at gas pumps are increasing. One is the almost universal switch to self-serve pumps, which requires millions of people who are unfamiliar with the volatility of gasoline to handle it once or twice a week.

Also, today’s vehicles have more electronics--CD players, geopositioning systems, satellite radios, cruise control, on-board diagnostics and electronically controlled fuel injection. Those elements combined with nylon seat covers could create more static.

Other theories include the use of cold weather-formulated fuels that are more volatile, tires made with less carbon and more silica, having fill pipe cover releases inside the vehicles and automobile parts made of dissimilar materials such as plastic and metal.

LaPrade said if people will follow the following safety guidelines when refueling, they will reduce the chance for sparking a fire.

Always turn off your vehicle engine while refueling.
Stay near the vehicle fueling point during the process.
Never smoke, light matches or use lighters while refueling.
Don’t get back into the vehicle while refueling--even when using the nozzle’s automatic hold-open latch. If you must re-enter the vehicle, discharge static electricity build up when you get out by touching the outside metal portion of the vehicle, away from the filling point, before attempting to remove the nozzle.
Don’t overfill or top off your tank. The fuel dispenser will shut off automatically when the tank is full.

SOURCE: Dr. Jesse LarPrade, Extension Environmental Specialist, Alabama Cooperative Extension System

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