lmb@vicom.com (Larry Blair) (09/29/89)
In article <kZ8Jnzy00Xc7A3wY9o@andrew.cmu.edu> jk3k+@andrew.cmu.edu (Joe Keane) writes: =Larry Lippman writes: =>In any event, the propellant in a can of Pam is isobutane; scary to be =>intentionally spraying a mixture of ethanol and corn oil propelled by =>isobutane around a stove, huh? How the makers of Pam can afford the =liability =>insurance for their product is a mystery to me. = =Presumably because it's pretty safe. If a dozen people blew themselves =up every year because of this, i'm sure we'd hear about it. Here's my =analysis. If somehow you managed to spray it into an open flame, you'd =have a small blowtorch for a little while. It _might_ explode if you're =stupid enough to keep doing this for a while. Of course throwing it =into a fire is another matter... 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. The exploding can theory was one that my parents were quite fond of when I used to use spray cans as torches in my demented youth... There are some cans, notably whipped cream, that use nitrous oxide as the propellent. Of course I don't think any company would be stupid enough to, say, use it with an alcohol based product. I wonder what the flash point would be? -- Larry Blair ames!vsi1!lmb lmb@vicom.com
harris@cbnewsm.ATT.COM (jonathan.harris) (09/29/89)
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 into
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.
---------------------------------------------------------
Jonathan Harris research.att.com!allwise!harris
AT&T does not endorse anything said above.kohli@gemed (Software Surfer) (09/30/89)
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!!!