I saw a guy smoking and e-cig at the gas pump the other day. Dangerous or not?
You can put out a cigarette by dunking it in gasoline. I’ve done to prove that it can be done.
The burning ember isn’t hot enough to ignite the fumes. Lighting a match to light a cigarette IS a problem around gasoline fumes.
Note: I’m not responsible for any damages or injuries caused by you trying to put out a cigarette in gasoline.
I’d imagine your car’s engine, after stopping, is a million times hotter than the heating element of an e-cig.
The temperature of a lit cigarette is more than enough to light gasoline, but the gasoline itself is cold enough that your lit cigarette was quenched before it could heat the gasoline to the auto ignition temperature. Do it slowly enough, and you will get the fire you thought couldn’t happen. If you are unlucky, you could have a burning ember break off your cigarette and sit on the surface tension of the gasoline ignite it for you.
Mythbusters tried serval methods and were unable to get a lit cigarette to ignite gasoline.
An expert from the BATF tried over 2,000 times to get a lit cigarette to light gasoline - including using a vacuum device to increase the temp of the cig to simulate sucking on the cig. He/they were unsuccessful…
It may require ideal conditions, but the documentation is quite clear. The auto ignition temperature is below the temperature of a lit cigarette. It isn’t the temperature of the cigarette so much as the heat capacity of the gasoline. It’s the gasoline that has to reach auto ignition.
I can’t imagine it would be dangerous. The e-cig vaporizes the liquid with a piece of heated wire. The wire is enclosed in fiber soaked with the nicotine infused liquid. The liquid is encased in a tube of plastic or glass. You’d have to take it all apart to get to the element.
There’s never any spark made. If in some circumstance I can’t even imagine, you’d be in danger before any gas would be ignited.
Saying that it’s best not to use a vaporizer in a filling station is an expert opinion with only prudence in mind, not definitive. I am reminded of safety lamps in mines where you can have methane gas. The lamps do not ignite the methane but only because they are engineered not to. Same with methane detectors that use an open flame.
I’m curious to know what kind of gasoline was used to perform the tests, as in, what was the octane rating of the fuel.
I may be mistaken, but I’ve always had the impression that high octane gasoline, like the kind used for high performance racing engines, has a lower ‘flash point’ and will ignite easier than the gas that is commonly sold at the corner gas station. 
I do realize that some ‘racing fuels’ have other more volatile additives mixed in. I’m thinking more along the lines of 100+ octane gasoline, such as aviation gas.
Not clear how hot the heating element gets. It’s supposed to vaporize the nicotine, not burn it, so it may or may not get up to ignition temp.
Note also that the element doesn’t heat up until the smoker inhales through the device. He would have to be inhaling a flammable mixture of gasoline vapor and air in order to have a chance at ignition. Gasoline vapors are heavier than air, so when you’re filling your car, the only place you’re likely to find a flammable mixture is right next to the fill hole on your car, or directly below it (assuming a calm, windless day).
If the smoker drops the e-cig, well, he’s no longer inhaling on it, so the element won’t be hot. (it’s a small element, so it will cool off very quickly once eletrical power stops flowing through it).
This is only true with automatic e-cig batteries. Manual batteries have a button you can press and hold while not inhaling.
Regardless of the technical issues discussed, federal law under OSHA prohibits smoking or open flame while refueling.
Which brings up the obvious question: what is the definition of “smoking?” If I’ve got a device that vaporizes nicotine, but there’s no combustion going on (and of course no open flame), am I smoking?
You’ve actually got that backwards, possibly because it’s a bit counter-intuitive.
Higher octanes are harder to ignite. The idea is that higher octane fuel is not going to self-ignite under engine compression and ambient heat. A high-octane fuel-air mixture will wait at maximum mechanical compression (for instance, top dead center during the compression stroke) for an actual ignition pulse–the spark plug.
Higher octane gasoline can be compressed harder without self-igniting (knocking). Higher mechanical compression means more energy when ignition DOES occur.
Quoting pretty good Wiki article about Octane Rating:
Good to hear it’s not that much of a risk; I’d be worried otherwise that it might cause an e-xplosion.