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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

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.


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: 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:
> 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>


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