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Q & A: water on burning metal

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Most recent answer: 05/10/2012
Q:
Hi! I'm a firefighter with the Colorado Springs Fire Department, and on the Hazmat team. We had a recent hazmat question arise concerning 'the best' response to a large scale fire that includes a sizable body of burning metals. There was some disagreement between myself and a couple of my cohorts--whose names I shall not reveal out of respect for their privacy (Doug and Mike)--over whether or not water could ever be used as an extinguishing agent on burning metals. We all agree that putting water directly on any burning metal is a dangerous, possibly explosive, idea. But when I added that while all metals will burn at some temperature, there is a big difference between burning iron or steel in comparison to magnesium or lithium. They were of the opinion that once ANY metal was on fire the use of water should not be used because of the possibility of explosion. I say that's inaccurate. While I would not use water on burning phosphorus, sodium, lithium or magnesium (the classic example is the VW engine block), I would have no issue in putting water on redhot structural I-beams at a structure fire. Burning steel will COOL with the water, while the magnesium will REACT with it. Is that not correct? I would appreciate your help in resolving this question. And in all seriousness, it would be very educational for us. Regards, Bruce Monson
- Bruce Monson (age 43)
Colorado Springs, CO
A:
Wow, we really hesitate to give any shaky practical advice on anything as important and risky as what you and your anonymous friends (say Doug and Mike) do. However, you make a very good point. The alkaline metals directly react with water, so it's terrible to spray them with water. Steel does not. When you spray water on burning steel, the evaporation of the water carries off latent heat and thus cools the material. If the water vapor gets dense enough perhaps it can help reduce the oxygen concentration too.

The sorts of things that we really don't know include whether you can get pockets of trapped steam exploding and spreading bits of burning metal. Offhand, I wouldn't see why that would be worse for metal fires than for other fires. Your fellow firefighters must have much more practical knowledge about that side of things than we do.

Mike W.

(published on 05/10/2012)

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