Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!lll-crg!rutgers!sri-spam!sri-unix!hplabs!tektronix!uw-beaver!tikal!phred!earl
From: earl@phred.UUCP (Daddy Earl)
Newsgroups: sci.physics
Subject: Re: coal mines and candles
Message-ID: <804@phred.UUCP>
Date: Mon, 10-Nov-86 16:07:51 EST
Article-I.D.: phred.804
Posted: Mon Nov 10 16:07:51 1986
Date-Received: Tue, 11-Nov-86 20:06:45 EST
References: <238@sri-arpa.ARPA>
Reply-To: earl@phred.UUCP (Daddy Earl)
Organization: Physio Control Corp., Seattle, WA
Lines: 33

In article <238@sri-arpa.ARPA> JOHNSON%nuhub.acs.northeastern.edu@CSNET-RELAY.ARPA writes:
>
>     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


This is what is called a "DAVEY LAMP". It is named after Humphrey Davey, 
an early scientist. I don't know if he discovered the principle or if he
was just the one to put it to use. I was told that it works due to the 
fact that the metal screen conducts heat away from the gas too fast for
the flame to pass through. This can be demonstrated with a candle and 
some metal window screen. The screen has to be fine enough to do the job,
but still coarse enough to let light through. Marine supply houses sell
"flame screen" to put between the manifold and the carb. to help prevent
stack fires in boats. It is fun to play with. Try puting the flame of a 
butane lighter to a piece of screen and you will find that it won't go 
through. You can also light the gas on the other side of the screen and
it won't get back to the lighter. 

If someone has more information, I would like to hear it too. If my
information is incorrect please let me know (no flames please, I've 
got screen over my CRT so it wouldn't do any good anyway 8-) ).

Hope to hear more.