Davy lamp

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Davy lamp (drawing)

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Davy lamp (photo)

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 test for the presence of gases. If flammable gas mixtures were present, the flame of the Davy lamp burned higher with a blue tinge as shown by the gauge. Miners could place the 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). A flame is extinguished at about 17% oxygen content, air which will still support life, so the lamp gave an early indication of a problem.

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. The bare gauze was easily damaged, and once just a single wire broke or rusted away, the lamp became unsafe. Illumination from the safety lamps was very poor, and the problem was not resolved until electric lamps became widely available in the late 19th century.

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 were used for the Sydney, Athens,Torino,Beijing, Vancouver and Singapore Youth Olympic Games relays.They were also used for the Special Olympics Shanghai ,Pan American and the Central Afican Games relays. They will also be used for the London 2012 relay. The lamps are still made in Eccles. They have recently produced a modified version of the lamp which will burn Ghee, as used in Hindu flame ceremonies.

Electronic gas detectors are now widely used in collieries and detect methane by its slow combustion on a catalyst chip. The rise in temperature is detected and a warning emitted by the device, known as a methanometer. However it is still a legal requirement to operate a UK Coal Mine that a Protector Flame Safety Lamp is used for gas testing. These are carried by Pit Deputies who are usually responsible for 15 men.

External links

• Popular Science video showing an experiment that demonstrates the principle of the Davy lamphr:Rudarska sigurnosna svjetiljka