Q&A: Non-Sparking Metals Can Still Spark

Question: Occasionally when getting out of my car I feel something like a “static electricity shock” when I touch objects outside my vehicle. Like a shopping cart or gas pump. Is there any danger of this causing a fire when I’m fueling up? — SB, Santa Fe, NM

Answer: Yes, as you can see in this security camera video. It’s rare, but it can happen under the right conditions. Your car can build up a static charge from friction with the road and air, depending on atmospheric conditions like temperature and humidity. Usually the electric charge leaks off into the air fairly quickly when you stop. Most vehicles have many sharp points and edges that enhance the corona discharge.

I should also note that the metals used for gas pump nozzles and fuel tank inlets are “non sparking” alloys containing combinations of metals that do not spark when struck. These include alloys of copper, nickel, aluminum, beryllium, and titanium. Newer nozzles and inlets are also coated with a dense plastic to provide a further safety margin. So if you do insert the nozzle into the fuel inlet a little too quickly or forcefully, no sparks will be generated.

That’s not what happened in this video, provided by the Petroleum Equipment Institute (PEI) as a PSA. The spark here was caused by static electricity. Note how, after inserting the nozzle, the customer returns to her seat in the car. Many seat fabrics or covers are highly triboelectric. The act of sliding into that seat, and then sliding out back out, put a sizeable electric charge on her body. This could also be the cause of the “static electricity shock” SB asked about.

In the video, the static-charged customer then reached for the nozzle to remove it. Even though it was non-sparking metal, all metals still conduct electricity. When she touched the nozzle charge jumped from her body through enough of an air gap to ignite the gasoline vapors. She was lucky to escape without severe burns.

The video is from 2004, so there may or may not have been a plastic coating on the nozzle and/or fuel inlet. Either way, despite the dielectric properties of most plastics, sparks from a sufficiently high static charge can still get through. The charge will find its way to the nearest electrical ground, and if there’s an air gap and gasoline fumes, the spark could ignite a fire.

As a further PSA, let me recommend a simple safety tip: When you get out of your car at a gas station, before you touch your gas cap or the fuel nozzle, place your hand flat against a metal surface on the gas pump or other external structure. They are likely well grounded and quickly absorb any excess charge on your body. If you feel a “static shock” when you do this, then you may have just dodged a bullet.

Next Week in Sky Lights ⇒ The True Shape of Raindrops

Why Astronauts Stumbled on the Moon
The True Shape of Raindrops