Horsey keep your tail up

[TimberWolf]

No. I think he kicked the wall of the metal chamber with his steel shoes causing a spark but also driving a nail into the nerve in his hoof making him bite down in surprise. What he forgot was that he had metal fillings in his upper and lower frontal hook teeth. This resulted in sparking.... and also some smoke which reminded him we was gasping so he sat down and got out a fag and his zippo lighter. Put the fag in his mouth and light up taking a long slow wonderful drag. Upon exhaling he started coughing hard, so hard in fact he let out an involuntary fart which ignighted from his ciggy and blew the bleedin doors orf.... simple if you think about it really...

A slightly simpler explanation is that either there was combustible material in the oxygen rich air (e.g. hay particles) , or the horse burnt a horrible death (hair caught fire) that caused a secondary explosion that blew the chamber apart.

[TimberWolf]

Must have been a bit of a loud bang if they heard it 30 miles away.

The Apollo one you mention seems to be have been more of a hiss, probably because the pressure vessel was a lot weaker than the horse box. But what's more of interest is that it was a fire that went on for some 17 seconds before boom time, rather than immediate explosion. The fire created the boom.

Only 17 seconds after the first indication by crew of any fire, the transmission ended abruptly at 6:31:21 with a cry of pain and then a hiss as the cabin ruptured after rapidly expanding gases from the fire over-pressurized the CM to 29 psi (200 kPa) and burst the cabin interior
http://en.wikipedia.org/wiki/Apollo_1#Fire

[northernladuk]

At 95% it reacts with everything.

Especially at 22psi.

I would assume that the woman was outside the chamber operating the controls, rather than in there with horsey.

Probably got totalled by the door, which is the weakest part.

I think Zeity's comment above is most probably the cause!!!!

[DimPrawn]

I found a picture of the horse after it was boiled.

Not a pretty sight.

here

[Churchill]

Hell of a BBQ if you can find the bits...

[Troll]

Just did a quick search on what elements oxygen reacts with, but it turns out the question should be what doesn't it react with.

Everything burns in Oxygen

[EricBartlett]

Everything burns in Oxygen

Helium?
Neon?
Argon?
Only asking like.