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jaydeehess
2002-Sep-27, 03:38 AM
In a documentary about a string of arsons in which the accellerant was solid rocket fuel (which set these arsons apart from the run of the mill type) It was said that water poured on the flames dissociated into hydrogen and oxygen which then migrated to cooler regions and explosivly recombined.

Anyone know at what temperature H2O will dissociate?

DogB
2002-Sep-27, 04:41 AM
On 2002-09-26 23:38, jaydeehess wrote:
In a documentary about a string of arsons in which the accellerant was solid rocket fuel (which set these arsons apart from the run of the mill type) It was said that water poured on the flames dissociated into hydrogen and oxygen which then migrated to cooler regions and explosively recombined.

Anyone know at what temperature H2O will dissociate?


This sounds questionable to me. You will start to see initial dissociation at around 1800K but complete dissociation to diatomic hydrogen and oxygen species will require at least 3500K. These figures are rough as this is pressure dependent.

Solid rocket fuel may be able to achieve these temperatures (?) but I still can't visualize it. Water at these temperatures is pretty hard to contain. Any hydrogen/oxygen evolved would recombine fairly quickly. After all there is a significant ignition source nearby.

Dog

(Edited because I appear to have lost the ability to spell)

<font size=-1>[ This Message was edited by: DogB on 2002-09-27 01:01 ]</font>

p9107
2002-Sep-27, 12:08 PM
How would you obtain solid rocket fuel?

Laser Jock
2002-Sep-27, 12:49 PM
On 2002-09-27 08:08, p9107 wrote:
How would you obtain solid rocket fuel?



Just a guess, but maybe with a model rocket engine.

Chemist
2002-Sep-27, 01:20 PM
I can't think of what really makes this fire so unique to produce that phenomenon. The dissociation temperatures sound about right in terms of magnitude but some fires have previously gotten this hot and there were no problems with dissociation of water before.

The second problem I see is the basic kinetic theory of gases. Dissociated water would be a gas at this temperature. Gases expand to occupy larger volumes. They don't contract to smaller, more concentrated volumes.

Unless I know more details about the fire, I'd say that whatever explosion occured was likely from a backdraft. Using solid rocket fuel may seem unusual as an accelerant (it is strange to use this), but accelerants are only used to start the fire so I don't see this fire being any more unusual than any other I know of. Solid rocket fuel is good because it burns at high temperature and will cause the fire to spread rapidly. It's still a stupid choice for an accelerant because it's easily traceable.

Karl
2002-Sep-27, 01:46 PM
On 2002-09-27 09:20, Chemist wrote:
Unless I know more details about the fire, I'd say that whatever explosion occured was likely from a backdraft. Using solid rocket fuel may seem unusual as an accelerant (it is strange to use this), but accelerants are only used to start the fire so I don't see this fire being any more unusual than any other I know of. Solid rocket fuel is good because it burns at high temperature and will cause the fire to spread rapidly. It's still a stupid choice for an accelerant because it's easily traceable.


I remember seeing this show, or one like it. They were baffled because there was no trace left, yet steel beams were being consumed by the fire. I suspect that it was not actual rocket fuel being used, but only the oxidizer, ammonium perchlorate.

TinFoilHat
2002-Sep-27, 01:46 PM
Doesn't burning magnesium have this effect?

Chemist
2002-Sep-27, 02:27 PM
On 2002-09-27 09:46, Karl wrote:

I remember seeing this show, or one like it. They were baffled because there was no trace left, yet steel beams were being consumed by the fire. I suspect that it was not actual rocket fuel being used, but only the oxidizer, ammonium perchlorate.

That sounds like a *very* hot fire. I can see lot's of oxidizing agent being able to burn/melt steel. You typically don't need large amounts of accelerant to start a fire but there seems to be a lot in this case. Do you remember how much perchlorate there was? I'm still of the impression that dissociation of water has little to do with it.

I guess this topic doesn't have much to do with astronomy but I like chemistry.

2002-Sep-27, 03:12 PM
486.HUb'.disclaimer applied
On 2002-09-27 09:20, Chemist wrote: To?
My guess? Oxy-Accetlene reac 44oo +
{figure from memory}[know to be unreliable]
(anyway torch some water and see)
I doubt the story {I assume it was some TV Time}
most likely late night about the 9 or 10 PM slot
perhaps the 11 oclock NEWS..
My understandin was that besides a high tempature
an IRON catalist must be present to do the disassociation [ again from Memory }

David Hall
2002-Sep-27, 03:29 PM
Here's a dissenting opinion I just dug up off of Google. I assume it's about the same show.

http://yarchive.net/explosives/thermite.html

Chemist
2002-Sep-27, 03:43 PM
On 2002-09-27 11:29, David Hall wrote:
Here's a dissenting opinion I just dug up off of Google. I assume it's about the same show.

http://yarchive.net/explosives/thermite.html


Alas, a little probing for details and everything starts to make sense. The thermite scenario makes a lot more sense. I guess the program wanted to sensationalize things with a crackpot theory instead of consulting with an expert or two. I personally find reality much more interesting.

2002-Sep-27, 04:12 PM
On 2002-09-27 11:29, David Hall wrote: To: HUb's 486
Here's a dissenting opinion I just dug up off of Google. I assume it's about the same show.

http://yarchive.net/explosives/thermite.html
------
this one reminds me of my HUb' contra/ IRAN/Contra
what can i say? it was May 18th 1980 as I recall:
the chemical Question "PUT2ME" was what does the Sulpher taste in the Troudale Deep well water Mean
I got a thermometer from the head chemist and ran about measuring well water tempature which was 55 deg just like the chemist said..Anyway long story but I said Why of course it can mean only one thig Mt. Hood will erupt ..(sigh) it Was Mt St. Hellens (50 miles away)? & in Washington.. I guess tha Sand Won?

jaydeehess
2002-Oct-02, 06:01 PM
Thanks all. Yes it was "Day One" as I recall since the description of the show is dead on.

Shows what having only a rudementary knowledge can do. I believed the show but with an explanation from someone with more knowledge it all makes sense. Now I'm pissed off because I was taken in by pseudo science crap.

David Hall
2002-Oct-03, 08:04 PM
On 2002-10-02 14:01, jaydeehess wrote:
Thanks all. Yes it was "Day One" as I recall since the description of the show is dead on.

Shows what having only a rudementary knowledge can do. I believed the show but with an explanation from someone with more knowledge it all makes sense. Now I'm pissed off because I was taken in by pseudo science crap.


You had the sense to check the facts and not just accept it wholeheartedly. You should count yourself among the those who weren't taken in. /phpBB/images/smiles/icon_smile.gif

Cloudy
2002-Oct-05, 10:37 AM
Also worth mentioning -

Even if such dissassociation/recombination of H20 did happen, it would not increase the energy of the fire or explosion. By the law of the conservation of energy - you dont get any more energy recombining H2 and O than you spent by splitting them up.

I guess it could, however, spread out the energy of the explosion or fire so that it would cover more area.