Is it unsafe....
 

To fill a running vehicle with gas?

Depends how fast you're driving...

The Mythbusters say yes, but their methods are hardly scientific. Err on the side of caution? ;)

"What did you ask, I'm on my cell phone smoking a Camel!"

No, personally I don't think it's unsafe. However, it very well may trip the check engine light to come on since it would pick up the open gas cap as an emissions/EVAP system failure methinks.

Olden days (20+ years ago) it was standard practice.

Best response :)

Like most things in life, you can do it and get away with it 999,999 out of 1,000,000 times. But you have no idea when that 1 time is going to happen when it kicks you in the crotch.

Similar to IMSB failure.

It's as safe as using a cell phone at a gas station

I think the concern is about a difference in potential between the gas pump and the car which may result in a spark. Given the location of where that spark is going to jump if it does, it definitely could end badly.

Here it is the law, and a gas station attendant will not turn on the pump for you until you turn off your engine.

Its safe, but as mentioned before, you can get a CEL and also, the tank will not fill completely.

Why would you feel the need to ?

Single digit weather. Cab cools off very fast. More for vehicles in general not our P cars. Want it to warm up since I don't let it run to warm up at the house. It's cooooold!!!

I wonder how this would relate to plugging in an electric car if the engine was on. Would the spark be like free electricity or would you be charged for it?
:D

Would refrain from smoking while doing so.

The owner of a tiny gas station near me always smokes a cigar while pumping gas !

I saw some kid doing this at a gas station. I turn to the guy close to me and ask...is she really smoking a cigarette? He looks at me and shakes his head. By the time he looked again, I was speeding out of there like I stole gas or something. What a retard!!!

This scene comes to mind:
http://stream1.gifsoup.com/view6/308...as-fight-o.gif

Last March a gentle man was killed at a BP station in my area doing this. I'll pass.

It's physically impossible to ignite gas or gas vapor with a lit cigarette as I understand it.