What common activity exposes a person to the explosive power of 26 sticks of dynamite?

The answer: Handling one gallon of gasoline.

Filling vehicles at self-serve pumps requires millions of people to handle gasoline on a regular basis. Static electricity — common in cold, dry conditions — can create a spark when the driver touches the fuel nozzle. In rare circumstances, the static spark can ignite gasoline vapors, causing a flash fire.

No one knows for sure how many gas pump fires are caused by static electricity. However, 176 static fires were reported to the Petroleum Equipment Institute from 2000 to 2010.

Approximately half of the refueling fires involved the driver getting back into the vehicle while the gas still was flowing into the tank. When the driver stepped out of the vehicle and touched the nozzle to complete the fill-up, a static spark ignited the fumes. I first heard of this phenomenon several years ago at an Extension conference from a colleague in Indiana who was injured in just such a fire.

How does it happen?

When you pull into a gas station to refuel your vehicle, you open and shut the car door, open the fuel tank cover, touch the pump to begin fueling, and touch the nozzle on the pump — all before the gasoline starts flowing. Any static electricity that was picked up in the car has been dissipated several times.

But the danger comes if you get back into your car during fueling. The friction of synthetic materials of the car seat and your clothing might create static electricity, especially during these dry, cold winter months. If you leave the car door open and don’t touch any other metal before reaching for the gas nozzle, that static charge can be released at the nozzle, creating the potential for a flash fire.

More than three-fourths (78 percent) of the victims of refueling fires are women? Why? Women are more likely to return to their vehicles during refueling for personal safety, to check on child passengers, get money or credit cards from their purse, get warm or use the phone. Additionally, the synthetic fabrics of women’s clothing and hosiery are more prone to static build-up when in contact with vehicle upholstery fabrics.

To be safe at the gas pump, follow these safety guidelines:

1. Always turn off your vehicle engine while refueling.

2. Stay near the vehicle during refueling.

3. Never smoke, light matches or use lighters while refueling.

4. Do not get back into the car during refueling. If you must re-enter your vehicle, discharge static electricity when you get out by touching something metal (your car door, a different gas pump, etc.) before reaching for the gas nozzle.

5. To avoid gasoline spills, do not overfill or top off your tank. The fuel dispenser will shut off automatically when the tank is full.

6. When filling a portable gasoline can, always place the container on the ground and keep the pump nozzle in contact with the container while refueling. Containers never should be filled inside a vehicle, in the trunk, on the bed of a pickup or on the floor of a trailer. The carpeting and truck bed act as insulators, allowing static electricity to build up in the can while it is being filled. That static electricity could create a spark between the container and the fuel nozzle.

If a flash fire occurs during refueling, you should leave the nozzle in the vehicle and back away. Shut off the fuel at the pump, using the on-off lever or an emergency shut-off switch. Notify the station attendant at once so all pumps can be shut off with master emergency controls.

In the event of a fire, the natural tendency is to pull the nozzle out of the car tank. However, the flames will ignite the stream of gasoline like a flame-thrower, causing widespread property damage and the very real potential for human injury. There is not enough oxygen in the car gas tank to make it an explosion risk, so the best thing to do is leave the nozzle in place and let any flames burn out after the pump is shut off.

There is more information about static electricity gas pump fires online, but one good place to start is the Extension fact sheet developed by the Indiana Extension agent who experienced this phenomenon herself. You can find it at www.extension.purdue.edu/cfs/programs/gaspump/resources/gaspump-handout-long.pdf.

Linda K. Beech is Cottonwood District Extension agent for family and consumer sciences.