From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: alt.engr.explosives
Subject: Re: Fire extinguisher bomb
Date: 4 Dec 1995 06:13:08 GMT
Organization: Consulting Chemist
Lines: 47

In article <Pine.ULT.3.91.951203145931.2186A-100000@selway.umt.edu>,
Scott R Clark <mickeyd@selway.umt.edu> says:

>> >        Ok, I can see the carbide making pressure in the bottle, but what
>> >source of ignition would it have?  Would it make enough pressure to bust
>> >it open without O2 and ignition (like a dry ice bomb?)
>> >                Scott
>>
>> Acetylene rupturing a container at high pressure does not
>> need an external source of ignition.
>>
>> Jerry
>
>        Uh, maybe I didn't make myself clear, but, what I asked was
>weather or not carbide would make *enough* acetylene gas to build up
>enough pressure to bust the bottle open.  No, a pressure explosion (like
>the dry ice bomb I cited earlier, or a steam explosion) dosn't require
>igniton.  But, then, like I said, thats not what I asked.

OK.

1.) Acetylene from carbide can generate enough gas
pressure to rupture any container you can devise. If
it has not already done so prior to the time of simple
cold gas pressure rupture, it will probably explode
chemically at the time of that rupture.

2.) Acetylene, below the rupture pressure of a fire
extinguisher, can explode spontaneously, i.e. without
a spark or flame or oxygen. It does not tolerate high
pressures well. That is why it is shipped and stored
in acetone solution.

3.) unless you were watching a pressure gauge, it would
be difficult to determine which of the two mechanisms
was responsible for rupture. In the case of a strong
cylinder, I might bet on mechanism #2.

4.) It could even happen, under the right conditions,
that two or more explosions would occur in the cylinder
prior to rupture by either mechanism.

Jerry

From: John De Armond
Newsgroups: rec.pyrotechnics
Subject: Re: Acetylene
Message-ID: <k_mka0j@dixie.com>
Date: 12 May 92 20:02:06 GMT

njs@scifi.uucp (Nicholas J. Simicich) writes:

>In article <1992May10.055212.22999@hpcvaac.cv.hp.com> billn@hpcvaac.cv.hp.com (bill nelson) writes:

>The point is, I've gone through a number of bottles of acetylene.
>None of them have decomposed.  Never has acetylene noticeably
>decomposed while in the gas lines (where the pressure is typically 3-5
>PSI).  It burns real well, with lots of heat and energy, of course.
>And we know that acetylene can't be pressurized to thousands of PSI
>like more stable gases, like O2 or N2, (or air) it has to be dissolved
>in acetone, and that the presure that it comes from the gas house at
>is about 200 PSI.  And I've never heard any explosions from the nearby
>welding yard or pressurized gas seller (where I go to by my supplies).
>It seems to be a stable industrial chemical.

You may not be aware of it but acetylene DOES decompose in a welding
rig.  If you've had your torch any time at all, particularly if you've
used it with high gas pressure (close to 15 psi) to, for example,
run a rosebud, remove the acetylene hose from the regulator and
look inside.  You'll see the tube lined with soot.  This soot comes
from decomposed acetylene.  Fortunately it normally proceeds slowly
and quietly.


>I contend that if it is possible for acetylene to decompose by itself,
>other than in the rarest of circumstances, it would not be a useful
>industrial chemical, and I would need special permits to purchase and
>transport even one bottle (this is NY, a fairly protective state).

Well no.  The safety and econazis go after the weak sheep in the herd
and/or the sensational targets.    Witness the public flagations
regarding PCBs contrasted against the fact that craftsmen and women
routinely use hydrofluoric acid to etch glass and use cyanide for
silver and gold plating.

A more reasonable indication of the relative risk is the insurance
rates associated with various activities.  There are maybe 4 acetylene
filling stations in the US.  You don't even want to think about what
their insurance rates are.  Visit one of these sometime if you get a
chance.  Observe how it has characteristics of a bunker.

I personally treat acetylene with the upmost respect.

>Finally, I wouldn't
>take a chance on using large diameter hose (like garden hose) for the
>gas lines.  I think I'd want to use regular acetylene/oxygen welding
>hose, as (1) large diameter garden hose would waste a lot of gas for
>purging, if indeed it was possible to do a good job and

Oh lord no.  Not unless you want the explosion back at your feet.
I use common clear Tygon-type tubing because it is cheap and can be
easily slid over  nipples.  Unless you bury the hoses, they will be
damaged by the blast so welding hose would be awful expensive.

One thing that's never been satisfactorily explained to me is how the
acetylene in the gas space in an acetylene cylinder is stable at the
~200 psi typical of a full cylinder.  Barry?

John

From: John De Armond
Newsgroups: rec.pyrotechnics
Subject: Re: old cutting torches (instead of acetylene)
Message-ID: <j!yvvzj@dixie.com>
Date: 30 Apr 93 18:13:01 GMT

markt@harlqn.co.uk (Mark Tillotson) writes:

>The material was calcium carbide, and the gas evolved pure acetylene.
>In contrast the pressurised gas bottles used in commercial
>oxy-acetylene equipment contain a mixture of acetylene and
>methyl-acetylene, otherwise using pressurised bottles would FAR TOO
>DANGEROUS! Pure acetylene self-detonates at modest pressures, in the
>presence of catalysts, and is generally not the sort of thing you want
>to store anywhere!

NO!  At least not in this country.  Aceetylene tanks are filled with
an inert material (used to be asbestos, now looks like mineral wool)
saturated in acetone.  Pure Acetylene gas is dissolved in the acetone
at about 125 psi of pressure.  The absorption process takes several
days during which the cylinders are slowly rotated on horizontal
rollers.  Each tank varies in its ability to absorb the gas so the
volume absorbed is marked on each tank.  I used to own a welding gas
distributorship and have trucked many a load of cylinders to the
fill station.

The acetylene gas is made by reacting caclium carbide with water - just like
in a miner's lamp.  For large volume uses such as metal fabrication shops
the same kind of acetylene generator is used.  It consists of a tank that
holds the acetylene and fed with a water supply.  The water flow is regulated
to maintain about 15 psi in the generator.  The process is thus self-regulated.
I used to stock 100 lb bags of calcium carbide for customers who had
generators.

John

From: John De Armond
Newsgroups: rec.pyrotechnics
Subject: Re: old cutting torches (instead of acetylene)
Message-ID: <_j1vcap@dixie.com>
Date: 3 May 93 02:24:11 GMT

khartman@fnalo.fnal.gov (Ken Hartman) writes:

>> NO!  At least not in this country.  Aceetylene tanks are filled with
>> an inert material (used to be asbestos, now looks like mineral wool)
>> saturated in acetone.  Pure Acetylene gas is dissolved in the acetone
>> at about 125 psi of pressure.  The absorption process takes several
>           ^^^^^^^^^^^^^^^^^^^

>	When I was taught to use a cutting torch, I was told that Acetylene
>could explode at pressures greater than 15 psi, hence the red scale on the
>regulator gauge above 15 psi.  What's the scoop?  Also, I was told that the
>Acetylene tank should always be stored upright, never laid down.  True or false
>and why?

If you'd looked at the regulator you'd have noticed that the high pressure
gauge was probably calibrated 400 psi full scale.  The acetylene does not
become unstable in the tank because there is essentially no free volume
and because the acetone stabilizes it.  There IS some breakdown of
acetylene in the high pressure passages in the valve and regulator but
the volume is kept very low so there is no explosion hazard.  One can see
the byproduct of this breakdown in the soot that forms inside a regulator
that has had any significant use.

Tanks absolutely should be stored and used upright.  Short term horizontal
storage is not harmful but long term storage and/or use while horizontal
can cause acetone drawoff.  Burning acetone is somewhat less productive
than burning acetylene not to mention more spectacular.  In addition to
capacity acetylene tanks are rated for maximum drawoff rate.  If that rate
is exceeded there will be acetone carryover.  That is why higher volume
applications have several tanks plumbed in parallel.

John