The feared spark was not a radio signal
The danger people imagined was that a mobile phone’s radio waves might ignite gasoline vapor near a pump. That idea sounds plausible: gasoline vapor can catch fire if it meets an ignition source. But a phone’s ordinary radio transmission is not a tiny flame, and the signal itself is not the main hazard at a filling station.
The real concern is an electrical spark. Gasoline gives off vapor, especially around the open filler neck and pump nozzle. If enough vapor mixes with air, a spark can ignite it. Phones contain batteries and electrical components, so keeping them away from fuel seemed like a sensible precaution—but under normal use, those enclosed components do not ordinarily produce an exposed spark capable of setting vapor alight.
Static electricity is the more credible risk
A person can build up static charge while sliding across a car seat or moving in and out of a vehicle. If they return to the pump and touch the metal nozzle, that charge may jump as a spark. Because the nozzle is right beside the fuel opening, the spark can occur where vapor is present.
That is why safety advice has focused on staying outside the vehicle while fueling and touching a metal part of the car away from the filler opening before handling the nozzle if you do get back in. The phone became the conspicuous suspect; static buildup was the less visible mechanism.
A warning that outlasted its original rationale
Phone bans and warning signs spread as a precaution, even though the feared phone-triggered fires were not established as a routine hazard. The broader rule—avoid distractions and keep anything that could create an ignition source away from fuel—still makes sense. But the memorable threat was not a handset’s signal somehow setting gasoline ablaze. It was a spark near a cloud of vapor, with static electricity providing the more plausible route.
