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From: kohli@gemed (Software Surfer)
Newsgroups: sci.med,sci.chem,sci.bio
Subject: Re: Spraycan blowtorches (was Re: Butane death)
Keywords: kaBlooey! flame thrower
Message-ID: <1084@mrsvr.UUCP>
Date: 29 Sep 89 20:25:01 GMT
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Reply-To: kohli@gemed.med.ge.com (Software Surfer)
Followup-To: sci.med
Organization: GE Medical (Applied Science Lab)
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In article <4851@cbnewsm.ATT.COM> harris@cbnewsm.ATT.COM
(jonathan.harris) writes:
>In article <1989Sep28.170222.15851@vicom.com> lmb@vicom.COM (Larry
>Blair) writes:
>+No way it could explode.  All of the combustion is taking place
>+when the atomized mist mixes with the air.  To explode, there
>+would have to be an oxidant inside the can.  Even in a fire,
>+the explosion would be from the increased internal pressure,
>+not from combustion.
>
>This is a dangerous misconception. There are cases of people
>being badly burned and even fatally while trying to use an
>aerosol can torch.  Would you bet your face(or your life) that
>air has not been inadvertently pumped nto the can during the
>manufactoring stage? These aren't designed as torches so it is
>unlikely manufacturers take special precautions to insure no
>air gets in the can.
>

I'm going to be Mr. Bad Judgment for just a few minutes.
Let's suppose that there was air in the can.  That means
that your risk is increased by two factors:

	1. *If* the contents of the can reached the flash point,
		it might (probably would, depending on the ingredients
		and how they're mixed) explode because of the O2
		which is assumed to otherwise be absent.

	2. The aerosol is now faster burning, possibly
		explosive, depending on droplet size, dispersion,
		etc.  So you'd have less time to react to a
		"burnback" situation, where the flames are moving
		faster toward the can, and could potentially make
		it to the nozzle prior to cutoff.

Here's the tricky part: how likely is it *really* that
the flame can make it *through the nozzle*?  Consider that
it is the nozzle itself which converts the liquid to
spray.  Is the liquid itself explosive?  Not usually--
the availability of O2 to most flammable liquids is
limited to the surface, which constrains the rate of
burning to be something less than an explosive rate
due to the fact that only the vapor phase can burn.
I would, therefore, expect the nozzle to prevent
explosions even if there were air in the can (unless,
of course, there was an almost unobstructed air/vapor
path from the nozzle into the can!).

Don't try this at home, kids!!!