Davy lamp

The Davy lamp is a safety lamp with a wick and oil vessel burning originally a heavy vegetable oil, devised in 1815 by Sir 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.

Davy had discovered that a flame enclosed inside a mesh of a certain fineness cannot ignite firedamp. The screen acts as a flame arrestor; air (and any firedamp present) can pass through the mesh freely enough to support combustion, but the holes are too fine to allow a flame to propagate through them and ignite any firedamp outside the mesh. The first trial of a Davy lamp with a wire sieve was at Hebburn Colliery on 9 January 1816.



Gas Detector

The lamp also provided a crude test for the presence of gases. If flammable 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 (asphyxiant gas), the lamp flame would be extinguished (black damp or chokedamp).

Comparison with Geordie lamp

There was some controversy, since George Stephenson also produced a similar safety lamp in 1816 called the Stephenson generally and locally within the North East coalfields the Geordie.

Supporters of each man seem to have regarded the other as having plagiarised their man's idea. The Geordie lamp had a glass inside the tubular gauze with a copper cap; the air was fed from below. The Davy lamp was simpler and cheaper, and was popular with mine owners.

There were 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. The gauze rusted easily in the damp mines, making the lamp hazardous. The Geordie lamp could become unsafe if the internal glass was broken (as it became an oversize Davy). Both original lamps were faulty, and led to attempts at improvement, by using multiple gauzes above the flame, and with a glass surround to improve illumination. They were poor sources of light and the situation did not improve until the introduction of electric hand lamps in the Victorian period.

Accident rate

The introduction of the Davy lamp actually led to an increase in accidents in mines, as the lamp encouraged working mines that had previously been closed for safety reasons.

One reason why the lamp caused an increase in the accident rate was that the men continued to work in unsafe conditions due to the presence of methane gas. The other reason why there was an increase was that there should have been an installation of extractor ventilation fans installed at each mine to reduce the concentration of methane in the air. This would have been expensive, and thus they were not installed by mine owners. The lamps also had to be provided by the miners themselves, not the owners, as traditionally the miners bought their own candles at top price in the company store. The installation of fans became required after laws requiring minimum air quality standards were introduced.

Modern Lamps

The modern day equivalent of the Davy lamp is the Protector Garforth GR6S flame safety lamp which is used for firedamp testing in all UK coal mines. A modified version of this lamp is used to transport the Olympic Flame for the torch relays. They have recently been used for the Sydney, Athens, and Turin torch relays and have been used for the Special Olympics Beijing relay, they will also be used for the London 2012 relay. The lamps are still made in Eccles.

From http://en.wikipedia.org/