Idling Car while Filling up w/ Gas

I’m a relitively new driver who accidently left the engine on while filling up with gas yesterday. I was always told this is dangerous but before I left the station I asked the attendent who said that as long as I don’t ‘change states’ ie turn the car on/off etc while filling up there isn’t a problem.

So whats the straight dope?

The “obvious” risk is that heat or sparks from a running engine may ignite the gas fumes present while pumping. I don’t see how turning the engine off during fueling could cause a problem, but starting it up could be a problem. FTR I have never personally seen or heard of anyone’s car catching fire because of fueling with the engine running.

Another hazard, which has caused gas tank fires in recent memory is caused by getting back in the car after starting to fuel and then getting out again. If conditions are right, this can cause a static buildup in your body, then when you touch the metal nozzle on the gas pump the spark can cause the fuel vapors to ignite.

There are those who would tell you not to use your cell phone while fueling, also because of sparks, but this has generally been debunked.

A while ago, my car died as I was about to fill up. The guy across from me, tossed me his cables and opened his hood. Just I’m about to start up the engine, a hand enters the window and grabs my keys. The guy looked terrified…“What are you crazy…? You jump that car and you’ll kill us all!” There was gas all over the ground and a couple of people were pumping gas behind us. He was convinced all it would have taken was one spark…

He helped me push the car to the back of station, and jumped it. Apparently he spent the rest of the day, telling the tale of the two morons who nearly blew up his station.

If there really was ‘gas all over the ground’, then that manager did the right thing. Sparks are often created when you clamp the cables to the battery terminals.

Kill us all? I think the manager watched too many movies. Gasoline has a very specific fuel/air mixture required to “explode.” I have seen gas burning inside a plastic gas container and it died out from lack of oxygen rather than exploding. Our fear at the time was that the container would melt before the fire died and spill burning fuel. We were young and stupid and at a bush party, we all lived to tell the tale. :slight_smile:

This was the subject of a lengthy thread last June. I’ll say now what I wrote then… I don’t think there’s any evidence that leaving the engine running increases the risk of fire or explosion. In that thread, nobody could produce a cite showing a single case where a gas-station fire was caused by leaving an engine running, and I don’t believe anyone offered a rationale explanation for why it’s dangerous to leave an engine running while the gas is being pumped, but not dangerous for the engine to be running while the car is entering/exiting the pump area.

I have no problem with avoiding the practice on “it couldn’t hurt” grounds, but I haven’t yet heard an explanation for how a non-defective running engine could spark an explosion while pumping, but not pose the same risk during normal operations.

If anyone can cite an actual occurence, or can explain the cause of the elevated risk, I’d be happy to stand corrected.

That’s very true, and it has saved the life of many an idiot. BUT, since you can’t easily tell when the gas has reached the proper "critical mass’ for a WHOOOOPH then you have to treat all gasoline spills as dangerous.

You’d think that it would be almost impossible to light gasoline fumes from the nozzle on fire from just a static electricity discharge, but it happens on average about half a dozen times a year. There’s close to 300 million people in the US, so if there’s a one in a million chance of something happening, it happens to 300 people every day.

Now sure, if you had the exact same situation (gas all over the ground and 2 guys with jumper cables) happen over and over, 99 percent of the time there wouldn’t be an explosion, but all you need is just once to have a pretty big disaster on your hands. With gas all over the ground you can easily start a large fire, which could easily catch one of the cars on fire, and once the car’s gas tank goes up it could easily catch a pump on fire, and once that goes it can take out a city block. There are some pretty impressive vidoes floating around the net of gas stations blowing up, and they aren’t Hollywood.

I probably wouldn’t have so much respect for it, but I saw a car pull over on the way home from college one day and everyone climbed out. Two minutes later you couldn’t even tell it had been a car. It burnt that quick. The firefighters (who arrived WAY too late) said basically yeah, cars go quick once they get going.

IMHO, the manager was right to throw a shit fit.

Let me play overly-cautious-ninnies advocate. “Non-defective” engine encompasses a whole lot of gray area. I’ve driven some clunkers in my day, several of which routinely produced a robust backfire when turned off. This backfire may not have had enough ‘spark’ to it to ignite gas fumes if you were funnelling said fumes into the tail pipe – but it might. You could certainly see the orange flash when it was dark. And let us not forget that older model cars sometimes had the gas cap in the rear, near or under the license plate…that’s pretty close proximity to the tail pipe. And the older cars didn’t have the vacuum on the gas tank nor that nifty little reducer that popped the dispensing nozzle off before a drop of overfill escaped. So maybe there is some merit, or at least was some merit to the ‘not changing states of the engine while filling.’

Also, a source of sparks from a running engine comes from worn-out spark plug wires. Hence the old yard-mechanic’s rule of knowing when to change your plug wires. With the car running (at night, in the dark, no headlights) open the hood and see if you see sparks. I’ve done that one before. There’s a bunch of rogue electricity running around under the hood when your plug wires are worn.

Now whether any of these factors could cause an explosion? I don’t know. But throw them into a sack with a some spilled gasoline on hot asphault in a Georgia August and I can see how the planets might align for something bad to happen.

Of course on the flip side, I’ve seen lots of folks sitting in an idling car, filling up and smoking a cigarette.


How about when you’re filling up and the car next to yours “changes states”? This happens all the time and no one thinks about it.

On the other hand, I think the puddle of gasoline on the ground is more dangerous than some people here are acknowledging. It isn’t necessary for gasoline to explode for it to cause damage. An open puddle of gas could catch on fire and burn for quite a while (as opposed to gas in a closed container). Of course, someone at the station should have cleaned up the puddle as soon as they noticed it.

I always thought this caution predated the now-dominance of automatic transmissions, and self-service stations.

Often parking brakes are poorly adjusted, and to be sure a manny-tranny car won’t roll you need to put it in gear, and shut off the engine.

At a full service station, the attendant knows you aren’t about to drive away if the engine isn’t running. He also knows he won’t be tangling with a fan when he checks your oil.

Finally, If somehow a large fuel spill does get ignited, it might be better if there were not a large fan forcing a strong draft under the vehicle.

Gotcha, but I still questiion whether an engine that is running for three minutes (or whatever) poses more of a risk than an engine that is running when you pull in, then started again and running when you leave. If anything, I think the greatest risk comes when you create sparks in your engine compartment when restarting the car.

I was gonna ask for a cite, but I found one myself. A study by the Petroleum Equipment Institute documents 162 fires caused by static while refueling from 1992-2005 (which I’ll stipulate averages to about 12 a year :slight_smile: )

In the PEI’s FAQ, they also state why they believe it’s dangerous to leave your engine running during refueling:

Both of those issues will still be true while you’re pulling into the pump, and if the exhaust components are hot enough to ignite gasoline, they don’t suddenly cool off when you stop the engine (gasoline’s ignition point is about 500 degrees F/280 C).

FatBaldGuy mentiond the myth of cell phones being dangerous. PEI says clearly: “In fact, PEI has not documented a single refueling fire caused by a cell phone or pager.”

It’s fascinating reading, and they talk about all sorts of things that cause fires at gas stations. Other than static, they seem to mostly be caused by people smoking, or other blatantly dangerous (and stupid) things.

Something that no one has touched on is the fact that some cars will check the evaporitive system for tightness when the engine is at idle.
So if your car is OBDII and it checks for leaks in the evaporative system at idle
If you happen to leave your car running and remove the gas cap
you are at the period of time when the engine management system is checking for a leak
Then you will get a check engine light.

If you are lucky and nice the mechanic might turn it off for free, the first time.