Davy Lamp
In the Davy lamp a standard oil lamp is surrounded by fine wire gauze, the top being closed by a double layer or gauze.
If firedamp is drawn into the flame it will burn more brightly and if the proportions are correct may even detonate. The flame on reaching the gauze fails to pass through and so the mine atmosphere is not ignited. However, if the flame is allowed to play on the gauze for a significant period, then it will heat up, sometimes as far as red heat. At this point it is effective, but in a dangerous state. Any further increase in temperature to white heat will ignite the external atmosphere. A sudden draught will case a localised hot spot and the flame will pass through. At a draught of between 4 and 6 feet per second the lamp becomes unsafe. At Wallsend in 1818 lamps were burning red hot (indicating significant firedamp). A boy (Thomas Elliott) was employed to carry hot lamps to the fresh air and bring cool lamps back. For some reason he stumbled or moved the lamp too quickly and triggered the explosion. At Trimdon Grange (1882) a roof fall caused a sudden blast of air and the flame passed through the gauze with fatal results (69 killed).
Poor copies and ill-advised "improvements" were known, but changing dimensions either reduced the illumination or the safety. The poor light compared to either the Geordie or Clanny eventually led to the Davy being regarded as not a lamp but a scientific instrument for detecting the presence of firedamp. Some pits continued to use candles for illumination, relying on the Davy to warn men when to extinguish them.
Read more about this topic: Safety Lamp, Oil Safety Lamps, Examples of Lamps
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