Flammability of gas vapors

[Traab]

Ok, so I was reading a story on Not Always Right, where a person was at the gas station complaining about bugs declaring how they need to install bug zappers because she was getting chewed up and another customer laughed at her for trying to get them all killed. But the thing is, how dangerous ARE gas vapors at a station? I cant imagine they travel any real distance before being so diluted by air they cant even ignite anymore. And im also pretty sure the pumps are designed to PREVENT excessive vapor leak as the smell of gas isnt particularly strong while pumping so how much is even getting out in the first place? Im fairly sure that during standard use, putting bug zappers like 10 feet away would be 100% safe, so how big of a spill would there need to be before those sparking zappers would be dangerous?

[Brother Oni]

Ok, so I was reading a story on Not Always Right, where a person was at the gas station complaining about bugs declaring how they need to install bug zappers because she was getting chewed up and another customer laughed at her for trying to get them all killed. But the thing is, how dangerous ARE gas vapors at a station? I cant imagine they travel any real distance before being so diluted by air they cant even ignite anymore. And im also pretty sure the pumps are designed to PREVENT excessive vapor leak as the smell of gas isnt particularly strong while pumping so how much is even getting out in the first place? Im fairly sure that during standard use, putting bug zappers like 10 feet away would be 100% safe, so how big of a spill would there need to be before those sparking zappers would be dangerous?

Bear in mind that the petrol station has to comply with various safety regulations (example), so is limited in what they can or can't permit, else they'll be slapped with a fine for safety violations.

Mythbusters have shown that a mobile phone is incapable of igniting petrol vapour (link) at optimal air concentration (between 1.4 - 7.6% air concentration), but the consulting expert later on says that static from people is capable of igniting petrol fumes as they are dispensing (4:15 onwards of the same video). Electrostatic discharge causing fuel ignition is a major issue in the fuelling industry (link).

To be honest, any activity or situation that raises the risk of ignition should be minimised or removed; just because the safety measures work under controlled conditions, it doesn't mean they still work once the average user gets to them, or once wear and tear sets in and regular maintenance isn't performed.

[Traab]

Bear in mind that the petrol station has to comply with various safety regulations (example), so is limited in what they can or can't permit, else they'll be slapped with a fine for safety violations.

Mythbusters have shown that a mobile phone is incapable of igniting petrol vapour (link) at optimal air concentration (between 1.4 - 7.6% air concentration), but the consulting expert later on says that static from people is capable of igniting petrol fumes as they are dispensing (4:15 onwards of the same video). Electrostatic discharge causing fuel ignition is a major issue in the fuelling industry (link).

To be honest, any activity or situation that raises the risk of ignition should be minimised or removed; just because the safety measures work under controlled conditions, it doesn't mean they still work once the average user gets to them, or once wear and tear sets in and regular maintenance isn't performed.

Yeah but all of that involves creating a perfect storm of conditions including being right next to the dispensing gasoline which was my point. IS there any danger, any at all, of a bug zapper sparking away say, 10 feet from the pumps? Would it require some sort of massive fuel spill before it could conceivably create enough gas vapor to reach said sparkers? I mean obviously they wont do it because why take any risk no matter how infinitesimal for such a meaningless reason, I just wondered what actual danger level it would create.

[Yora]

Im fairly sure that during standard use, putting bug zappers like 10 feet away would be 100% safe

There are millions of cars getting refuled every day. That adds up to a lot nonstandard uses.

There are videos around of people building big bonfires and soaking them in petrol, then igniting them a few hours late. Those fireballs indicate a really significant buildup of vapors on the ground. Very unlikely to happen, but when we're talking about gas station fires, even 1 in a million would be way too high.

[jayem]

Yeah but all of that involves creating a perfect storm of conditions including being right next to the dispensing gasoline which was my point. IS there any danger, any at all, of a bug zapper sparking away say, 10 feet from the pumps? Would it require some sort of massive fuel spill before it could conceivably create enough gas vapor to reach said sparkers? I mean obviously they wont do it because why take any risk no matter how infinitesimal for such a meaningless reason, I just wondered what actual danger level it would create.

I'd have thought if 10' were dangerous-dangerous there would be issues with cars starting, the lights in the shop and possibly even smoking areas (a search for which came up with numerous people commenting on smoking while fueling).
However (aside from the fact that this is intuition, and could be wrong):
a) If there is a freak large spill, drivers will have time to not start their cars, a passive ignition source will still be there.
b) If you allow a loophole...
c) As mentioned any specific refueling based 1/1,000,000 chance will happen something like 25 times a day in the USA.

[Ninja_Prawn]

It's worth bearing in mind that the pumps aren't the only part of the site where fumes are likely to build up - there will be vent pipes from the underground storage tanks and an interceptor/separator to extract petrol from rainwater runoff, both of which could well be close to the shop where you might put a bug zapper. If there are basements, pits or sumps on the site, heavier-than-air fumes can easily build up to explosive concentrations in those places. When you're thinking about safety, you have to look for the worst case scenario.

And yes, the lights in the shop are a risk - this explosion was blamed on a faulty light fitting - but at least lights aren't supposed to be sparking. A bug zapper is built specifically to do that! It's clearly a higher risk.

[Khedrac]

From what I heard, there did used to be a number of explosions at filling stations, however they were ended by getting the layout right for airflow to dispere fumes. That said, this is one of those areas where one has to ask if the benefit outweighs the risk.

Risk is measured as probability of occurring multiplied by severity of outcome.

A fuel explosion at a filling station has a high severity of outcome thus it is worth eliminating all the potential triggers one can, even if the probability seem negligible.

Even if there remain ignition triggers with a higher probability of occurrence that one cannot remove, it is still worth removing all the ones oone can.

Hence on the bug zapper - chance of it causing an explosion = really, really, low; but result of explosion = bad enough to make you put up with the bugs.