From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: A cool bottle trick !!!
Date: 15 Nov 1995 06:22:48 GMT
Organization: Consulting Chemist

In article <48beap$bed@dana.ncd.com>, Bob Lawrence <bobl@pcx.ncd.com> says:

>Just found out a neat bottle trick which involves lighting 
>alcohol fumes inside a 5 gallon glass bottle. The display is
>quite spectacular and no two burns are alike.
>
>Equipment:
>
>5 gallon glass bottle (I use a sparkletts)
>Isopropyl alcohol
>long fireplace matches
>Fireplace bellows (optional)
>
>Pour in a small amount of alcohol, cover the top with you hand
>and spin it around making sure it coats all part of the bottle.
>Stand it upright and light with the long matches. Sometimes you 
>have to stick the match down the neck a bit. You can also put
>the bottle on it's side with slightly different results.
>
>Anyway.. you get a cool blue flame that starts at the top and
>burns down to the bottom. Sometimes its an even burn, sometimes
>it will dance around. The fireplace bellows is helpful in
>injecting more air into the bottle which help to catch the
>flame and will also vary results.

Bob,

I don't want to spoil your fun, but messing with 5 gallons
of flammable gas mixture could buy you some grief. The lower
alcohols burn with a nearly colorless flame which appears
almost cool to the eye, but is actually quite hot.

Fuel air mixtures such a gasoline and air burn at the pokey
rate of about 2 feet per second. Sometimes the effective
speed is is higher because of moving gas currents or eddies.

All of this can change dramatically when such a mixture
goes from deflagration to detonation mode, burning at
thousands of feet  per second and generating an unconfined
pressure of 100 psi or more. Your rubbing alcohol is
potentially capable of doing the same thing. Boom.

Methane is less sensitive to detonation than most hydrocarbon
materials, but I have personally witnessed a methane-air
detonation in an unconfined volume not much larger than 
your bottle.

Believe it or not, a medium-size test tube of detonating 
gas can let out a bang like a modest firecracker. You
don't want to be holding that jug if it ever decides
to switch velocities.

Jerry

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: A cool bottle trick !!!
Date: 19 Nov 1995 21:09:28 GMT
Organization: Consulting Chemist
Lines: 45

In article <48mie1$7cv@ixnews5.ix.netcom.com>, alithia@ix.netcom.com (K.
L. Hanson ) says:

>In <48c0vo$62d@geraldo.cc.utexas.edu> glhurst@onr.com (Gerald L. Hurst)
>writes: 

[Snip]

>> Your rubbing alcohol is
>>potentially capable of doing the same thing. Boom.

[Snip]

>  Doesn't rubbing alcohol have a high water content?  It really doesn't
>burn that well...IMHO

This is one of those cases where a little bit of chemistry can 
be a dangerous thing.  Rubbing alcohol comes in two concentration,
70% and 90%.  They naturally burn quite differently, but the
question is "do their vapors explode differently?"

The answer is "No."

When alcohol burns the vapor above the liquid is replenished by 
evaporation from the surface. The alcohol vapor pressure, being
a colligative property is greatly depressed in the case of the 
70% material and the evaporating molecules must diffuse through
surface layers enriched in water concentration and actively 
vaporizing substantial quantities of steam under the influence 
of the flame. The result is an anaemic, sputtering flame.

However, in the case of a vapor explosion, the alcohol solution
obviously has enough vapor pressure to reach above the explosive
limit, and, in fact, to the optimum enrgetic stoichiometry.
Furthermore, in the vapor phase, the water is limited to less
than the equilibrium vapor pressure of pure water, i.e. less
than about 20 mm or 2-3 percent of the exploding mixture. Note
that this amount of water is no greater than would otherwise
be be there if you evaporated pure alcohol on a humid day.

Conclusion: There is little difference between pure alcohol
and rubbing alcohol when dealing with vapor explosions. 

Ain't chemistry grand????


Jerry

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: A cool bottle trick !!!
Date: 22 Nov 1995 11:04:10 GMT
Organization: Consulting Chemist
Lines: 77

In article <DIEF9o.Iu@quest1.questconsult.com>,
tam@quest1.questconsult.com (Timothy Melton) says:

>In article <48c0vo$62d@geraldo.cc.utexas.edu> glhurst@onr.com (Gerald L.
>Hurst) writes:
>
>[stuff deleted]

>I think you are confusing explosions with detonations.  Explosions can be
>wither deflagrations of detonations.  The difference between deflagrations
>and detonations is the rate of propagation of the flame front.

Thank you for the kind advice. There are many people, including my
wife, who think I am confused - although generally not about the
difference between "detonation" and "deflagration."

Your idea of "unconfined" may not be the same as mine. If you 
consider an open ended shock tube as confined then what term
would you use for a 5 gallon glass jug without a stopper? Is
a baffled open container "confined" or otherwise?

I take it you believe that an open test tube of gas can deflagrate 
so rapidly that it makes a bang. Since you are apparently 
knowledgeable about such fast "deflagrations" perhaps you would
share with us the mechanism by which the heat transfer from
the point of origin is rapid enough to cause the noise. Convection?
Radiation?

There are a lot of people who would agree with you that methane,
specifically, will not undergo a DTD transition in free space
initiated from the center.  OR, are you telling us that this gas 
or isopropyl alcohol, for that matter, may not detonate in some real 
life simple semi-confined or baffled environment? I'm talking about
simple situations like 5 gallon jugs or vented steel drums or even
a common oven with the door ajar.

What I think I heard you say was "Well, even if it does go bang
in a more or less open container it really wasn't a detonation,
it was just FAST.  Hmmm. How fast was it?

You say:

>     The ONLY methane detonations I am aware of were 
>     HE initiated, and most of these required a
>     mass of HE nearly equal to the mass of methane 
>     involved.

I understand your problem. Next time use more methane. The
initiating shock needn't be any greater than a few hundred PSI
so your wasting the first 4,000,000 psi of your HE.  The 
reaction with pure methane is best run with oxygen and works
best in small tubes.

I have seen natural gas explode with an ear ringing blast from
an open oven which had accumulated just the right mixture as 
that door was opened and the match was shoved under the lightly 
baffled burners. The shock exiting from those couple of cubic 
feet blew out the window, but did not burn the face or clothes
of the fellow with his face at the oven. That is a very small
amount of gas reacting very swiftly.  When you experience it, you
know it isn't just an extra fast "whump" as we all so often hear
when we light ovens and barbecues. 

I've handled numerous cases in which natural gas ranging from
about 15 cu ft of mixture up to a large buildings full of
gas exploded. The smaller explosion moved a couple of walls
and a roof and badly burned an occupant by flash, whereas the 
larger one blew hard enough to mangle a hotel across the street. 
The small explosion was a classical deflagration. The large 
explosion could have been either or both. But that tad of gas 
in the oven DETONATED. Maybe it was the impurities - maybe it 
was the baffling, but it made me a believer in avoiding somewhat
confined gaseous fuels, especially when they are not methane.

As I recall, someone recently posted that a glass liquor bottle
(cap off for ignition) blew up, not swooshed. That must have 
been one of those rapid convection deflagrations.

Jerry 

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: A cool bottle trick !!!
Date: 24 Nov 1995 08:17:24 GMT
Organization: Consulting Chemist
Lines: 20

In article <BILLW.95Nov23234836@puli.cisco.com>, billw@puli.cisco.com
(William ) says:

>    What I think I heard you say was "Well, even if it does go bang
>    in a more or less open container it really wasn't a detonation,
>    it was just FAST.  Hmmm. How fast was it?
>
>Is there a term for reactions that propagate faster than the speed of
>sound in air, but slower than the speed of sound in the material itself?
>This would allow an unconfined non-detonation to produce a "bang", I think.
>It might explain some of those controversial substances like flash...

Of course there is, bill. Smokeless powder deflagrating up the 
barrel of a rifle is propagating its reaction just as fast as 
the bullet moves, which varies from sub to supersonic at least
with respect to air as the bullet accelerates. When we speak of 
detonation, we mean a reaction propagating through the reaction 
medium above the speed of sound in that medium at the 
temperature ahead of the shock front. At least I do :)

Jerry

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: A cool bottle trick !!!
Date: 25 Nov 1995 21:19:04 GMT
Organization: Consulting Chemist
Lines: 55

In article <4975k2$bsd@lys.vnet.net>, murr@lys.vnet.net (murr rhame) says:

>billn@PEAK.ORG (Bill Nelson) writes:
>
>>Flash, among other rapidly burning materials, are self confining. Spread
>>that flash out in a thin sheet, and it will burn quite quickly, but without
>>the bang.
>
>Is there a formal definition for self confining?  Would this apply to any
>material which can produce a supersonic discharge confined by only a flat
>surface and the material itself?  Is there a formal term for the
>transition from subsonic discharge to supersonic discharge?  For example,
>with a given muzzle loader and black powder powder grade there is a
>minimum charge to fire an unconfined blank which makes a bang.  Below this
>"critical mass" of powder the discharge makes little sound.  Is there a 
>formal term for this transition? 

Imagine that you have a sphere of liquid propellant of very large
dimensions ,which you ignite in free space at the exact center. As
the deflagration reaction travels outward with imagined perfect
symmetry, the unburned shell of restraining liquid material is 
accelerated like an expanding balloon until the thinned surface
ultimately approaches the particle velocity of the expanding hot
gases. This terminal surface expansion rate would be supersonic
with respect to air. 

We can run the same thought experiment with an infinitely large 
shallow pool of the same liquid, initiated over its entire bottom 
surface at the same instant. I leave the design of the igniter to
others.

In real life we can't set up experiments like those above, but
one can imagine that a huge pile of propellant might give a
reasonable imitation thereof. After all these materials do it 
in gun barrels with lead. Why not with their own self-accelerated
substance.

Btw, using the bubble gum analogy, you can also simply let the hot 
gasses suddenly break through the more slowly accelerating shell
after pressure has built up. Small masses can't do this because
the surface area to mass ratio is so great that the gasses leak
through before much pressure can build up or they simply poof
the powder away. Building blow up with a terrible racket from
natural gas deflagrations because the increasing pressure cannot
vent the large volume of gas through the cracks under the doors
and the a/c ducts.  

At some rather large mass, the effective surface area of the pores 
in the outer shell of a pile of powder becomes as small in 
proportion to the volume of that powder as is the area of the 
crack under the door to the building volume. An exaggeration, I 
admit, but it makes the point.


Jerry

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: A cool bottle trick !!!
Date: 26 Nov 1995 04:47:44 GMT
Organization: Consulting Chemist
Lines: 36

In article <498li7$o4p@lys.vnet.net>, murr@lys.vnet.net (murr rhame) says:

>If I'm not mistaken, a couple of ounces of fast flash powder in a pile can
>self confine to the point of producing a sharp report even when lit from
>the top of the mass.  I presume the gas discharged by the burning mass
>raises the presure at the flame front high enough to increase the burn
>rate.  Again, quantities of flash below a certain mass will only produce a
>"poof" without a significant report.  Slight confinement can a big
>difference in the burn rate of flash powders. 

Murr,
I believe I remember you pyro folks mentioning that flash
develops a velocity of at least a couple of thousand feet
per second and probably considersbly more. Although this
might not qualify as a detonation per se, it does indicate
that the particle velocity of the expanding cloud is
faster than the speed of sound in air. I would expect that
cloud to act just like a solid or liquid piston moving at
comparable velocity.

When I used the examples of liquid and solid propellant
piles, I let the expanding surfaces be condensed not
because it needs to be so, but to help those less familiar
with these phenomena more easily visualize it.

I used large piles of material because I was thinking in terms
of very slow materials. In the case of flash, a little will do.

I think you are right on with your unconfined BP in a barrel.
I'll bet that mix of unburned and burned material is being
accelerated up the barrel and reaching the 1100 ft/sec
mark before the muzzle. The flash does the same thing, but 
does not need the barrel.

Jerry

Newsgroups: rec.pyrotechnics
From: tam@quest1.questconsult.com (Timothy Melton)
Subject: Re: A cool bottle trick !!!
Date: Mon, 27 Nov 1995 15:04:35 GMT
Lines: 159

Gerald L. Hurst writes:

>In article <DIEF9o.Iu@quest1.questconsult.com>, tam@quest1.questconsult.com
>(Timothy Melton) says:
>>
>Your idea of "unconfined" may not be the same as mine. If you 
>consider an open ended shock tube as confined then what term
>would you use for a 5 gallon glass jug without a stopper? Is
>a baffled open container "confined" or otherwise?

Confined as well.  Generally, an unconfined VCE needs to be able to expand
in 3 dimensions.  Confinement for "Unconfined" vapor cloud explosions is
provide by local obstructions such as pipe racks, or process equipment.
I would consider a shock tube to be quite confined, while as the L/D ratio
of the tube shrinks at some point I would consider it to be unconfined.  
There is clearly a gret area here, but I would generally consider most 5
gallon glass jugs to be confining.  

>I take it you believe that an open test tube of gas can deflagrate 
>so rapidly that it makes a bang. Since you are apparently 
>knowledgeable about such fast "deflagrations" perhaps you would
>share with us the mechanism by which the heat transfer from
>the point of origin is rapid enough to cause the noise. Convection?
>Radiation?

No.  Simply "shocking up" the air in front of the flame front.  The
magnitude of this acoustic wave is far less, generally, that that of the
subsonic blast wave that is produced by the expanding combustion gases.  To
put it simply, the flame front generates a shock wave.  If the flame front
can acceerate to keep up with the shock wave, you have a detonation:
esentially a coupled shock-reaction zone.  For a substance like
cyclohexane, the flame velocities will jump from subsonic up to about 1750
m/s generating overpressures in the range of tens of bar.  There are
several references demonstrating this behaviour.  A couple are:

"Transition to Detonation in Fuel-Air Explosive Clouds", I.O. Moen, Journal
of Hazardous Materials, v.33 (1993) 159-192.

and

"Understanding vapour cloud explosions - an experimental study", R.J.
Harris and M.J. Wickens, Communication 1408, The Institute of Gas
Engineers.

Finally, a good, general look at UVCEs can be found in:

"Unconfined Vapor Cloud Explosions", Keith Gugan, Gulf Publishing Company,
1978.

I can send you the bibliography from my dissertation if you'd like a more
comprehensive guide.

>There are a lot of people who would agree with you that methane,
>specifically, will not undergo a DTD transition in free space
>initiated from the center.  OR, are you telling us that this gas 
>or isopropyl alcohol, for that matter, may not detonate in some real 
>life simple semi-confined or baffled environment? I'm talking about
>simple situations like 5 gallon jugs or vented steel drums or even
>a common oven with the door ajar.

It is quite possible that a 5 gallon jug could provide sufficient
confinement for certain gas mixtures to undergo DDT.  I'd think it would be
much more likely in a steel drum.  I suspect that the glass jug would fail,
however well before the transition occured for most common gases.  this is
also the reason I suspect that methane in a oven would NOT undergo DDT: the
door, unless it was somehow clamped in a partially open position, whould
sever the same role as blast panels do in buildings relieving the pressure
and preventing a DDT.  If you had a more reactive gas, like acetylene or
ethylene oxide, you might well generate a detonation.

>What I think I heard you say was "Well, even if it does go bang
>in a more or less open container it really wasn't a detonation,
>it was just FAST.  Hmmm. How fast was it?

Less than the speed of sound in the combustion products.  Remember, just
because the reaction is progressing at less than sound speed does not mean
that there is no acoustic wave generated.  Think of the 'pop' you sometimes
here when lighting a bunsen burner.  Surely you are not implying that there
must be a detonation for that to occur?


>You say:
>
>>     The ONLY methane detonations I am aware of were 
>>     HE initiated, and most of these required a
>>     mass of HE nearly equal to the mass of methane 
>>     involved.

Sorry, I forgot to include the caveat: unconfined methane detonations.

>I understand your problem. Next time use more methane. The
>initiating shock needn't be any greater than a few hundred PSI
>so your wasting the first 4,000,000 psi of your HE.  The 
>reaction with pure methane is best run with oxygen and works
>best in small tubes.

Yes, you can detonate methane in shock tubes, especially if you enrich the
mix with oxygen.  In fact, as I understand it, most any fuel-air mix can
undergo ddt in a shock tube, given a sufficiently large L/D.  Again, I
do not consider a shock tube unconfined, especially when you are talking
about high l/d tubes.  

>I have seen natural gas explode with an ear ringing blast from
>an open oven which had accumulated just the right mixture as 
>that door was opened and the match was shoved under the lightly 
>baffled burners. The shock exiting from those couple of cubic 
>feet blew out the window, but did not burn the face or clothes
>of the fellow with his face at the oven. That is a very small
>amount of gas reacting very swiftly.  When you experience it, you
>know it isn't just an extra fast "whump" as we all so often hear
>when we light ovens and barbecues. 

Nope.  A deflagrating explosion can generate overpressures of up to about 1
atm (or 1 bar).  It takes only about 1 kPa, or about 0.01 bar to break a
window.  Had there been a detonation with the associated overpresure in the
tens of bars range, it would have demolished the house and not just blown
out a few windows.  There is an interesting report somewhere around here
that show what was left of a building that was filled with 9kg of propane
and subsequently detonatated using small HE charges.  All that was left
were matchsticks.  And no, there was not nearly enough HE to do that kind
of damage.

>I've handled numerous cases in which natural gas ranging from
>about 15 cu ft of mixture up to a large buildings full of
>gas exploded. The smaller explosion moved a couple of walls
>and a roof and badly burned an occupant by flash, whereas the 
>larger one blew hard enough to mangle a hotel across the street. 
>The small explosion was a classical deflagration. The large 
>explosion could have been either or both. But that tad of gas 
>in the oven DETONATED. Maybe it was the impurities - maybe it 
>was the baffling, but it made me a believer in avoiding somewhat
>confined gaseous fuels, especially when they are not methane.

I still doubt that the gas in the oven detonated unless it had a
significant amount of reactive impurities in it.  And if it was regular
town natural gas, that is unlikely.  

>As I recall, someone recently posted that a glass liquor bottle
>(cap off for ignition) blew up, not swooshed. That must have 
>been one of those rapid convection deflagrations.

Very likely.  All you have to do is build up enough pressure in the
container to cause it to fail.  In the case of a container with a "small
enough" opening, the product gases can not escape as fast as they are
produced so the pressure can build rapidly in the container leading to a
rupture.  You can blow up a bottle with dry ice and water and no detonation
is involved.  Rapid pressure release and the accompanying noise when a
vessel fails has little or nothing to do with the mechanism by with the
pressure was generated; in this case, whether it was by deflagratin or
detonation.

Again, i'll be happy to mail you or even post a short bibliography on the
topic of vapor cloud explosions.  

Tim
-- 
Tim Melton                    tam@questconsult.com
Quest Consultants Inc.        http://www.questconsult.com/
P.O. Box 721387               (405) 329-7475
Norman, Ok 73070-8069         Fax: (405) 329-7734

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: A cool bottle trick !!!
Date: 28 Nov 1995 07:37:26 GMT
Organization: Consulting Chemist
Lines: 46

In article <DIpJ7n.GE3@quest1.questconsult.com>,
tam@quest1.questconsult.com (Timothy Melton) says:
>
[Interesting post snipped. It's worth reading.]

I agree with most of what you say.

Except perhaps that I do not believe there is any reaction
mechanism other than detonation by which a gas in an open
test tube can react fast enough to produce a bang. I say this
merely because I cannot visualize any form of energy transfer
which is rapid enough to build up sufficient pressure in that
geometry without merely venting with a whoosh or schloooooop.
I do not include hypothetical esoteric mechanisms such as 
photon activation.

Now a whiskey bottle has better confinement, but you're still
going to have trouble figuring out how those gases swirled
arouund fast enough to transfer the heat with enough rapidity 
to keep the pressure from simply bleeding away with a whoomp.

I'll grant you that the natural gas bang I observed may have 
been the result of some accumulation of other flammable impurities.
I say this because I am well aware that CH4, as hydrocarbons go,
is reasonably resistant to detonation except under conditions we 
both understand.

BTW the exploding test tube contained phosphine bubbling off
of calcium phosphide, and it ignited spontaneously. It may
have contained diphosphine as well.

You know, in the case of alcohols and the like burning in
a bottle, we should consider the possibilities of secondary
reactions. The same is true of my oven explosion.

As an example, suppose that precombustion or even a pilot light
produces carbon monoxide or some alcohol oxidation product. Then
you have a new game afoot.  We see secondary explosions sometimes
when fuel rich explosives are shot underground.

BTW, I have propagated Al dust/oxygen detonations through
hundreds of feet of 3/16 inch or less PE tubing and liquid
explosives in hypodermic needle-sized metal tubing.

Just reminiscing and speculating.

Jerry

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: A cool bottle trick !!!
Date: 30 Nov 1995 07:11:14 GMT
Organization: Consulting Chemist
Lines: 25

In article <49ipot$ql4@earth.njcc.com>, billmcd@pluto.njcc.com (Bill
McDermott) says:

>Hydrogen/Oxygen bubbles produce a very loud bang when lit with a match. 
>Is this a detonation or are mere soap bubbles providing sufficient 
>confinement to cause a bang in a deflagrating mixture? Or is hydrogen an 
>exception to the rule because of the high stoich. flame speed? 

I personally believe that H2/O2 mixes near stoichiometry simply
detonate readily. The mixtures are notoriously sensitive to
initiation and this implies that a modest shockwave is sufficient
to propagate the reaction.. It is true that hydrogen diffuses
more rapidly than other gases because of its low molecular weight
and therefor burns faster than most fuels.

The flame speed of hydrogen is probably greater than that of 
acetylene and several times that of propane.

This is a complicated area so keep an open mind despite what
you hear from people like me.

BTW, one method of determining flame speeds is by photographing
the explosions of bubbles.

Jerry

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: sci.physics,rec.pyrotechnics,alt.engr.explosives
Subject: Re: What is the most powerful manmade explosive other than nuclear?
Date: 30 Apr 1996 01:00:43 GMT

In article <3184DF8D.169F7B66@questconsult.com>, Timothy Melton
<tam@questconsult.com> says:

>This sounds good, but I see at least one problem.  Flares would most likely 
>NOT cause even an EtO cloud to detontate.  In general, for unconfined 
>clouds, you need a detonating explosive to initiate a detonation in the 
>cloud.  The flammability limits for EtO are, by the way, 3.6% - 100%.
>It's not hard to get a flammable mixture.  Plus EtO is easy to detonate
>or to get to undergo DDT compared to many other fuels.

Tim, you and I have gone around this point before. I agree with you 
that it is difficult if not impossible to get a cloud of methane/air
in free space to shift from deflagration to detonation and that it 
would be no piece of cake to pull it off with gasoline vapor. I 
suspect, however that flares might well do the trick with EtO. 
I have pretty good reason to believe it might even work with 
aliphatics in the mineral spirits range given really good dispersion 
and just the right degree of vaporization on the lean side at ignition.

Maybe not :)

Jerry (Ico)

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: sci.physics,rec.pyrotechnics,alt.engr.explosives
Subject: Re: What is the most powerful manmade explosive other than nuclear?
Date: 1 May 1996 05:23:38 GMT

In article <3186058F.7331C734@questconsult.com>, Timothy Melton
<tam@questconsult.com> says:

>Gerald L. Hurst wrote:
>
>> In article <3184DF8D.169F7B66@questconsult.com>, Timothy Melton
>> <tam@questconsult.com> says:
>>
>> >This sounds good, but I see at least one problem.  Flares would most likely
>> >NOT cause even an EtO cloud to detontate.  In general, for unconfined
>> >clouds, you need a detonating explosive to initiate a detonation in the
>> >
>> >cloud.  The flammability limits for EtO are, by the way, 3.6% - 100%.
>> >It's not hard to get a flammable mixture.  Plus EtO is easy to detonate
>> >or to get to undergo DDT compared to many other fuels.
>
>
>Jerry,
>
>you write:
>> Tim, you and I have gone around this point before. I agree with you
>> that it is difficult if not impossible to get a cloud of methane/air
>> in free space to shift from deflagration to detonation and that it
>> would be no piece of cake to pull it off with gasoline vapor. I
>> suspect, however that flares might well do the trick with EtO.
>
>Re-read what I wrote above carefully. I said that a flare would 
>*most likely* not cause even an EtO cloud to detonate.  If I were
>designing a weapon system, I'd want to assure detonation.  
>
>> I have pretty good reason to believe it might even work with
>> aliphatics in the mineral spirits range given really good dispersion
>> and just the right degree of vaporization on the lean side at ignition.
>
>I'd be interested to know why you think this.  Experiments in tubes
>don't come close to reflecting what happens in more unconfined settings.
>To quote I.O Moen ("Transition to detonation in fuel-air explosive
>clouds", J. Haz. Mat., 33(1993) 159-192): "Weak ignition of vapour
>clouds in an unconfined, relatively unobstructed environment is 
>unlikely to result in DDT, even for relatively sensitive fuel-air
>mixtures."  Of course you can always argue degrees of obstruction
>and the relative sensitivity of the fuel ;-)
>
> 
>> Maybe not :)
>
>Or maybe.  Again, my point was that I'd rather insure detonation by
>using an HE initiator than hope it'd work with a flare.  Round and
>round we go, it seems. ;-)

Well, if you insist on using just ONE flare maybe so, but why would you 
not use several or several hundred dispersed ignition sources? That's
really not much more difficult than using one.

My main reason for believing it works reasonably well is that I have
an acquaintance who tells a pretty convincing story of having done
it. Mind you he wasn't in free space but on the level ground, but that's
where the practical applications are, so I figure it counts.

HE charges simply provide large low pressure adiabatic compression 
fronts so they probably are little more effective than a bag or
puff of, say, C2H2 mix or the like putting out a few hundred psi.

Maybe so, maybe no.

Jerry (ico)