Signs on gas pumps warning about the dangers of static electricity while refueling your car are not a gimmick.

Static electricity can spark a fire or explosion so be careful and heed the warning. Also, the risk is higher when the weather is cool or cold and dry and that’s just the type of weather we have been experiencing lately.

Static electricity is an electric charge caused by an imbalance of electrons on the surface of a material. It is usually 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.

“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,” Dr. Jesse LaPrade, an Extension environmental specialist, said. “In rare circumstances, the spark can ignite gasoline vapors around the fill spout, causing a brief flash fire.”

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

• Fifty 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 the gas pump nozzle from the car’s fuel pipe.
• Twenty-nine percent are caused when a person unscrews the gas cap.
• Twenty-one 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 more per week. Also, today’s vehicles have more electronics — CD players, geopositioning systems, satellite radios, cruise control, onboard diagnostics and electronically controlled fuel injection. Those elements combined with nylon seat covers could create more static.

Dr. LaPrade suggests people follow these safety guidelines when refueling to reduce the chance for starting 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 fueling point, before attempting to remove the nozzle.
• Don’t overfill or top off your tank. The fuel dispense will shut off automatically when the tank is full.

For more information on safety at the gas pump, go to www.cfs/purdue/extension/gaspump/.