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From: firth@sei.cmu.edu (Robert Firth)
Newsgroups: sci.physics
Subject: Re: coal mines and candles
Message-ID: <412@aw.sei.cmu.edu.sei.cmu.edu>
Date: Mon, 24-Nov-86 10:15:24 EST
Article-I.D.: aw.412
Posted: Mon Nov 24 10:15:24 1986
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>     At one time I was informed that early coal miners used candles on 
>their helmets to provide light in the mines.  This would cause an 
>explosion now and them because of coal gas build-up.  Someone 
>discovered that by putting a metal cage around the flame, the candle 
>could be safely used in the mine.
>     Does anybody know whether or not this is true, who discovered it 
>and why it works?
>Chris Johnson
>Northeastern University

The miners' safety lamp was invented by Sir Humphrey Davy.  It
works because the metal cage conducts the heat away sufficiently
to cool the burning gases below the ignition point, so the flame
cannot get out of the cage.

Incidentally, this still leaves the problem of the miner being
asphyxiated by the coal gas.  An additional feature is that the
candle flame burns bluish when gas is present, which warns the
miners.  Before that, they used canaries (when the canary drops
dead, move out).