MadSci Network: Chemistry
Query:

Re: How can a pile of coal combust?

Date: Tue May 19 09:37:10 1998
Posted By: Dan Berger, Faculty Chemistry/Science, Bluffton College
Area of science: Chemistry
ID: 893123594.Ch
Message:

How can a pile of coal combust?

The history teacher of my school came and ask me to explain to him how the USS Maine could have blown up. He said that the fuel, coal was stored in a place and that somehow this coal "spontaneously" combusted. I have my theories, but I am unclear how a pile of coal can blow up! Is this similar to the wheat silos that we blowing up.


On April 16, 1947, a freighter loaded with ammonium nitrate exploded after catching fire in the harbor of Texas City, Texas. Apparently the fire made the fertilizer hot enough to detonate; the fertilizer did not go off until at least thirty minutes after the fire started.

The reason ammonium nitrate can detonate is that it already has all the oxygen it needs, according to this equation:

On the other hand, grain silos can be destroyed by dust explosions, in which a fine dust is intimately mixed with air. Since combustion is a surface phenomenon, and dust has a lot of surface area relative to its mass, dust will burn very quickly indeed -- fast enough to cause an explosion.

Like grain (but unlike gunpowder, which contains saltpeter), coal doesn't carry its own oxidizer. So if the Maine explosion was caused by a coal bunker, it would have to be a dust explosion. For a ship lying at anchor, this seems unlikely; however, consider the following scenario:

We can't, of course, know exactly what happened on the Maine. But this seems as likely as anything, and rather more plausible than sabotage (what reason would Spain have for such an act?). The conclusion of the official Naval Board of Inquiry was that the explosion of an external mine had set off one of the Maine's powder magazines. This conclusion was made on the basis of the bending patterns on the shredded metal: some of it was bent in, most of it was bent out.

But the only possible scenario for the thing starting in the coal bunker is a dust explosion.

A bit of local pride: the captain's bathtub from the USS Maine is on display at the Hancock County Historical Museum, just down the road from yours truly.

  Dan Berger
  Bluffton College
  http://cs.bluffton.edu/~berger


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