I don't know how flame traps are fitted to shafts but the principal behind
them is that a porous, usually metal, medium is put in the path of the gas
and if a flame approaches from one side, the flame trap medium delays and
cools the gases sufficiently before they reach the other side so that they
cannot ignite gas there. The idea is that the gas travels at x m/s through
the trap and the flame at y m/s. The trap ensures that y<x so the flame can
never keep up with the gas and never reaches the other side.
The simplest flame trap is a plain gauze as in a Davy lamp (Remember using a
gauze in chemistry at school? The flame stays below but the heat comes
through.) Modern flame traps are deeper and made of knitted wire or layers
of gauze.
Regards
Nigel Dibben
Visit my website at <A HREF="http://www.dibben.org.uk">http://www.dibben.org.uk</A>
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