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Davy lamp

From Academic Kids

The Davy lamp is a safety lamp devised in 1815 by Humphry Davy. It was created for use in coal mines, allowing deep seams to be mined despite the presence of methane and other flammable gases, called firedamp or minedamp.

He had discovered that, to explode, the gas must be heated to its ignition temperature and that if such heating is prevented combustion cannot occur. If the flame in a lamp is surrounded by metal gauze to distribute the heat over a large area, the maximum temperature of the screen is below the ignition temperature of the gas. The first trial of a Davy lamp with a wire sieve was at Hebburn Colliery on January 9, 1816.

The lamp also provided a crude test for the presence of gases. If inflammable gas mixtures were present, the flame of the Davy lamp burned higher with a blue tinge. Miners could also place a safety lamp close to the ground to detect gases, such as carbon dioxide, that are denser than air and so could collect in depressions in the mine, if the mine air was oxygen-poor, the lamp flame would be extinguished (chokedamp).

There was some controversy, since George Stephenson also produced a similar safety lamp in 1815.

The Stephenson lamp (the Geordie lamp — possibly the route by which ‘Geordie’ became the familiar /affectionate epithet for Tynesiders) actually worked on significantly different principles. If the only way air could get to the flame was restricted (a baseplate pierced by a number of small-bore brass tubes was the usual way of doing this) and the lamp body above the flame lengthened, then the same amount of air could get to the flame, but would pass through the flow restriction at a velocity higher than the velocity of the flame in a firedamp (methane/air mixture. How far the difference was appreciated at the time is hard to say; supporters of both men seem to have regarded the other as having copied their man’s idea and copied it wrong. The Stephenson lamp (with no gauze around the flame) gave a brighter light and was popular with the pitmen. The Davy lamp was simpler/ cheaper to make and was popular with the mineowners.

There were supposed safety arguments on both sides: in principle, a poorly maintained (or badly designed) Davy lamp could overheat the gauze if it met a high concentration of methane. A more serious objection to the Stephenson lamp was that it stopped being a safety lamp if the glass was broken. In the long term, the Davy lamp (or at least the principle of a gauze enclosure round the flame) won out.

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