From: John De Armond Subject: Re: Preventing fires at gas stations Date: Wed, 01 Mar 2000 02:06:55 EST Newsgroups: rec.outdoors.rv-travel Richard Cochran wrote: > Also, in case anyone chimes in and says they leave their fridge on > while fueling and everything has been OK so far, I believe you, but > that still doesn't make it safe. True, as long as no fuel is spilled, > and not too many vapors are around, it's unlikely the fridge will > cause everything to go boom. However, prudence calls for always > keeping yourself at least "two dumb mistakes away from death". If the > fridge is lit, it only takes one more dumb mistake (a significant fuel > spill) to cause a serious problem, whereas normally it would take a > fuel spill PLUS a second dumb mistake of providing an ignition source. Before we get too carried away with this, a few facts ought to be entered into the record. Unless one hoses the side of the RV down with the gas hose, there are very few credible ways spilled gas can be ignited by a flame that far off the ground. Gas vapor is heavy and hugs the ground. If there is enough turbulence to bring the vapors up, they are diluted until they are not flammable. Unless the 'fridge vent is hosed. The fire codes explicitly recognize this. The NFPA building code now requires gas water heaters to be placed on a stand 18" off the floor to prevent it from being able to ignite gas vapors from spilled vapors. This value was chosen by testing which showed that unless sufficient gas was spilled to fill the whole room with a combustible mix, the vapors would not reach that high. On the commercial side, the NFPA requires the Class A, division I barrier (I think that's the correct reference) that separates the explosion-proof wiring from ordinary wiring at a gas station (or other environment where flammable vapors are present to be located no lower than 18" from the ground. Above 18", the wiring can be non-explosion-proof. Those little tees you see near the ground on gas station wiring conduit that has a leg coming off at about a 30 degree angle with a plug in the side arm is the barrier. Epoxy is poured in the tee to form the barrier. Another example of this is when Coke places a vending machine on the pump island. They sit it on an 18" stand so that the machine doesn't have to be explosion-proof. Far more likely to cause an explosion from spilled gas is the hot catalytic converter on the tow vehicle or MH. I wonder how many people who go through the hassles of turning off their propane before refueling ALSO wait long enough away from the pumps for the cat converter to cool off? None, I bet. Wonder how many of these people ever thought about the sparking contacts in those coke machines on the pump islands? Fine demonstration of the gulf between perceived risk and real risk. Since Winnebago/Itasca nicely has all the flues exiting on the opposite from the gas filler on my MH and the refrigerator's flame is at about chest level, I don't give it a second thought. John From: John De Armond Subject: Re: Preventing fires at gas stations Date: Sat, 04 Mar 2000 18:48:42 EST Newsgroups: rec.outdoors.rv-travel John wrote: > > Ok here it is the final profesional information on gas lp and natural gas > using Vapor density or specific gravity IE: as compaired to air as 1.0 > Propaine >Relative vapour density (air = 1): 1.6 sinker LEL(Lower > explosive limit): . . 2.1% (10% LEL, 2,100 ppm) > Natural Gas Sp.Gr(60°F): 0.72-0.76 floater > gasoline Sp.Gr(60°F): 0.72-0.76 floater > ammonia Relative vapour density (air = 1): 0.59 floater (your > refrigerator) (100PPM burns your eyes) 300ppm is IDLH immediatly dangerous > to life and health and is flammmable 15% (10% LEL, 15,000 ppm) Nope, sorry. 0.72-0.76 is the specific gravity of LIQUID gasoline, which obviously does float - on water. The term "specific gravity" has no meaning in the context of a vapor or gas. If you had looked here: http://www.msdsonline.com for gasoline, you would see that the relative vapor density is in the 3-4 range. That means that gasoline vapors are 3-4 times as heavy as air and sink like a rock. You'd also know that if you had ever taken quick look at the vapor plume emanating from an open gas can. > Bottom line turn it all off. Is 10 min of fueling worth your life, your > familys life or even your prized possesion Well, if that was the equation, the obviously 10 minutes isn't an issue. But it's not. Typical strawman argument of the safety (sic) establishment. The real question is, "Is 10 minutes of extra time worth it to address one minor source of possible ignition among many others?" The answer there is obviously, NO. Is the relative risk high enough? Again, the answer is no. To frame your question properly, you would ask "Is it worth the effort to turn your propane off, let your catalytic converter cool, hit the battery disconnect switch (to keep relays and other contacts from arcing), coast onto the pump island, wait for all other sources of ignition (other vehicles) to leave, pump your gas and then push your vehicle away from the pumps (so the arcing from the starter motor won't pose a risk)? The answer is obviously NO. This is the decision most people make, even though for most people, the relative risk decision is made subconsciously. While on the topic, I wonder how many people check to make sure the filler cap compartment is gas-tight to the interior of the motorhome? I discovered that mine wasn't after getting fumes inside the coach during refueling. The back side of the compartment was in the same space as the converter and breaker panel. Weigh the relative risks of gasoline seeping into electrical spaces vs the very remote possibility of spilled gas vapors reaching a lit refrigerator flame. Bet I can count on the fingers of one hand those who have even given this a thought. > REF: http://www.cdc.gov/niosh/npg/npgd0000.html#N > John Hotelling > FireChief (Ret) > EMT I Hazardous Material Instructor <soapbox mode on> Frightening thought that you train emergency responders if you put out this type of horribly wrong information. Teaching firemen that gasoline vapors rise will get them killed. Actually this is more the norm in my experience, so much so that I recently quit volunteering my time as a RADEF trainer to emergency responders. I experienced so many of these "authorities" who got the position by virtue of seniority and not education be absolutely, positively and without a shadow of a doubt flat wrong and refuse any evidence to the contrary. I got tired of fighting it. Folks ought to keep this in mind the next time you hear the latest hazard du jour pronouncement from a fire official. They do a wonderful job putting out burning things, most of the time. They would be ahead of the game to stop there. <soapbox off> John |