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Comment by sriram_sun | Hacker News Reader

> H2O is even worse as once the oxygen is split from the water molecule you are left with hydrogen which will combust and explosion might cause the molten fire to spread even farther

Yup, this is why you never douse an oil fire (say in the kitchen) with water. The fire will erupt! Seen it happen live. Fortunately the damage wasn't bad. One third-degree burn.

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A kitchen oil fire is a different effect. They're not hot enough to disassociate water molecules. What happens typically is that the water floats the oil, and the fire, remaining on top of the oil, spreads more rapidly.

Another effect is when the fire (and typically, the cooking vessel) are hot enough to vaporize the water. This rapid vaporization spreads oil droplets rapidly, allowing much more of the oil to burn at once. It can appear explosive, even though it's just rapidly-expanding steam spreading fine oil droplets.

Yeah in the case of water on burning kitchen oil it just makes a big fuel-air bomb if the oil is atomized enough. Kinda like one of these:

https://www.youtube.com/watch?v=i20zvZ-3MMw

Note the initial dispersion of some atomized material followed by a triggered explosion some time later.

I think "rapidly expanding and exothermic" is equivalent to "explosive" at least functionally.

I'd agree that it's explosive. I suspect they were trying to make a distinction between a detonation and a deflagration. A detonation is an explosion with a supersonic shock wave. A deflagration is an explosion without such a shock wave. An oil fire getting water dumped on it is a deflagration, but almost certainly not a detonation. A metal fire getting water dumped on it can result in a detonation. Detonations are vastly more destructive in general than deflagrations.

Exactly that. Thank you. You know better words for it than I do :)

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