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47879.  Thu Jan 26, 2006 1:33 pm Reply with quote


47880.  Thu Jan 26, 2006 2:06 pm Reply with quote

who has that much free time?

47897.  Thu Jan 26, 2006 3:43 pm Reply with quote

bobofel wrote:
is oxygen explosive itself? It is needed in combustion but does not burn itself.

You need a source of ignition of course but BOC includes an explosion warning in its hazards overview. Re-lighting a taper in a test tube of high oxygen content gas is not a fair representation of the risk of explosion. Combustable materials, things for the oxygen to oxidise, that would not normally explode may do so in the presence of elevated oxygen levels. Did you see the Brainiac when they left a safety dummy in a caravan with a lit cigarette and a bucket full of liquid O2? As soon as enough the O2 had evaporated BOOM.

Environmental effects of oxygen

Highly concentrated sources of oxygen promote rapid combustion and therefore are fire and explosion hazards in the presence of fuels.

Aluminium will oxidise quite well of course

Over the past 5 years, FDA has received 16 reports of aluminum regulators used with oxygen cylinders burning or exploding. These incidents caused severe burns to 11 health care workers and patients. Many of the incidents occurred during emergency medical use or during routine equipment checkout. FDA and The National Institute for Occupational Safety and Health (NIOSH) believe that the aluminum in these regulators was a major factor in both the ignition and severity of the fires

Last edited by Celebaelin on Thu Jan 26, 2006 3:50 pm; edited 2 times in total

47898.  Thu Jan 26, 2006 3:47 pm Reply with quote

Maybe whoever wrote the posts about colour blindness could paste them into the Dalton thread, since colour blindness was originally called Daltonism, after John Dalton?

47928.  Thu Jan 26, 2006 6:42 pm Reply with quote

bobofel wrote:
is oxygen explosive itself? It is needed in combustion but does not burn itself.

If it was every time a match was struck the room would be full of flames. In a pure oxygen environment lighting a match would be quite dramatic, but for oxygen to burn O2 would have to react with O2 to produce O2 & release heat

47954.  Fri Jan 27, 2006 5:08 am Reply with quote

Oxygen of course doesn't burn itself, per se, but causes other things to burn extremely violently. However, there are very few situations where you will have a large concentration of oxygen and a source of ignition, but not have a material capable of combustion, so it's safer to say that oxygen is a risk of explosion even if it's technically inaccurate.

47962.  Fri Jan 27, 2006 6:24 am Reply with quote

so it is still an explosion risk, but only when combined with other materials

47970.  Fri Jan 27, 2006 7:11 am Reply with quote

Or, to put it another way, many other chemicals are an explosion risk when combined with oxygen and some (eg Aluminium) are an explosion risk only when exposed to a highly oxidising environment such as elevated O2 levels / 100% ppO2.

When O2 levels are elevated what would not burn readily now will and what did burn may well explode. In the Brainiac example one would not normally consider the bedclothes etc as the sort of materials (!) that would be likely to explode (don't blow your nose too hard on that hankie it might go off) but unless there were other substances present in the caravan (oooh, cheaters) then explode they did, quite dramatically. If your opinion is that it was the bedclothes that were the critical element in this explosive mix then that is not an opinion we share.

Fortunately I have never seen an oxygen fire in the chemical engineering sense but the example in the Brainiac program behaved exactly as I thought (and to be honest in that instance rather hoped) it would.

<Edit> Superfluous and confusing 'only' removed

Last edited by Celebaelin on Fri Jan 27, 2006 7:52 am; edited 1 time in total

47972.  Fri Jan 27, 2006 7:19 am Reply with quote

Celebaelin wrote:
100% ppO2.

I don't understand this. What does pp stand for?

47975.  Fri Jan 27, 2006 7:41 am Reply with quote

partial pressure

partial pressure n.

The pressure that one component of a mixture of gases would exert if it were alone in a container.

So what I was talking about was a gas which was 100% O2 at a given pressure (not necessarily atmospheric) and all of that pressure is therefore exerted by the oxygen.

Come to think of it it's not a good or conventional way of expressing it but it is a quick way; 100% O2 at any given pressure would have been better.

47987.  Fri Jan 27, 2006 10:19 am Reply with quote

I see. Thank you :)

48346.  Mon Jan 30, 2006 8:56 am Reply with quote

Were'nt we talking about dynamite?

How much dynamite would it take to destroy a small, 3 storey house? Would it depend on where/how it was placed?

48356.  Mon Jan 30, 2006 9:41 am Reply with quote

It certainly would. You'd have to take into account the structural design and materials of the building's supporting walls and floors, and also the volume of the space into which the dynamite was installed, and how quickly the gases could get out of that space.

I've only ever managed to explode a catering-size can of baked beans with explosives, so that's probably not much help. If you're wondering, it made an interesting pointilliste spatter effect on the side of my friend's house, but for some reason his mother wasn't convinced of its artistic merit.

48363.  Mon Jan 30, 2006 10:37 am Reply with quote

At the other end of the scale, research undertaken by physicists from the Centre for Explosion Studies at the University of Wales in Aberystwyth concluded that an explosion of the 2,500kg of gunpowder Guy Fawkes was found with would not only have destroyed Westminster Hall and the Abbey but would also have caused severe structural damage to buildings two-thirds of a mile away. It isn't certain that the gunpowder would have exploded at all, however; some historians believe that it had decayed chemically so as to be no longer dangerous at all.

48384.  Mon Jan 30, 2006 11:42 am Reply with quote

Centre for Explosion Studies

Many comic pictures appear in my mind. Imagine the phone call to the buildings insurance people to get a quote: "...and what's the nature of your company's work?". Imagine the exam room at the end of term.

Fred has some first-hand experience of blowing up Houses of Parliament, I believe...


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