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Safety lamp used in flammable atmospheres

The Davy lamp is a safety lamp used in flammable atmospheres, invented in 1815 by Sir Humphry Davy. It consists of a wick lamp with the flame enclosed inside a mesh screen. It was created for use in coal mines, to reduce the danger of explosions due to the presence of methane and other flammable gases, called firedamp or minedamp.

German polymath Alexander von Humboldt, working for the German Bureau of Mines, had concerns for the health and welfare of the miners and invented a kind of respirator and "four lamps of different construction suitable for employment in various circumstances. The respirator was to prevent the inhaling of injurious gases, and to supply the miner with good air; the lamps were constructed to burn in the most inflammable kind of fire damp without igniting the gas. They were the forerunners of Davy's later invention, and were frequently made use of by the miners." Davy's invention was preceded by that of William Reid Clanny, an Irish doctor at Bishopwearmouth, who had read a paper to the Royal Society in May 1813. The more cumbersome Clanny safety lamp was successfully tested at Herrington Mill, and he won medals, from the Royal Society of Arts. The first trial of a Davy lamp with a wire sieve was at Hebburn Colliery on 9 January 1816. and a paper describing the lamp was formally presented at a Royal Society meeting in London on 9 November. efn| The mean maximum quenching diameter (the maximum hole diameter through which a flame (not an explosion) will not pass) for drilled holes in 1/32" thick brass plate was reported in 1968 to be 0.139 inches for methane/air mixtures. Davy's letter read at the 3 November meeting in Newcastle reported that his work on samples of firedamp had shown that explosions in flammable mixtures of firedamp with air would not pass through tubes of diameter less than 1/8". and raised a subscription for him of £1,000. In 1833, a House of Commons committee found that Stephenson had equal claim to having invented the safety lamp.

The lamp consists of a wick lamp with the flame enclosed inside a mesh screen. 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 Davy lamp was fuelled by oil or naptha (lighter fluid). 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. Lamps were equipped with a metal gauge to measure the height of the flame. 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 methane air flame is extinguished at about 17% oxygen content (which will still support life), so the lamp gave an early indication of an unhealthy atmosphere, allowing the miners to get out before they died of asphyxiation.

In 1816, the Cumberland Pacquet reported a demonstration of the Davy lamp at William Pit, Whitehaven. Placed in a blower " the effect was grand beyond description. At first a blue flame was seen to cap the flame of the lamp, – then succeeded a lambent flame, playing in the cylinder; and shortly after, the flame of the firedamp expanded, so as to completely fill the wire gauze. For some time, the flame of the lamp was seen through that of the firedamp, which became ultimately extinguished without explosion. Results more satisfactory were not to be wished " Another correspondent to the paper commented "The Lamp offers absolute security to the miner With the excellent ventilation of the Whitehaven Collieries and the application of Sir HUMPHRY's valuable instrument, the accidents from the explosion of' (carburetted) 'hydrogene which have occurred (although comparatively few for such extensive works) will by this happy invention be avoided". More generally, the Select Committee on Accidents in Mines reported in 1835 that the introduction of the Davy lamp had led to an increase in mine accidents;

The lamps had to be provided by the miners themselves, not the owners, as traditionally the miners had bought their own candles from the company store. Miners still preferred the better illumination from a naked light, and mine regulations insisting that only safety lamps be used (in response to an explosion at the St Hilda pit in 1839) to consider the prevention of accidents in mines had shown that mine ventilation in the North East was generally deficient, with an insufficient supply of fresh air giving every opportunity for explosive mixtures of gas to accumulate. A subsequent select committee in 1852 concurred with this view; firedamp explosions could best be prevented by improving mine ventilation (by the use of steam ejectors: the committee specifically advised against fan ventilation), which had been neglected because of over reliance on the safety of the Davy lamp. The practice of using a Davy lamp and a candle together was not entirely absurd, however, if the Davy lamp is understood to be not only a safe light in an explosive atmosphere, but also a gauge of firedamp levels. In practice, however, the warning from the lamp was not always noticed in time, especially in the working conditions of the era. The Regulation and Inspection of Mines Act of 1860 therefore required coal mines to have an adequate amount of ventilation, constantly produced, to dilute and render harmless noxious gases so that work areas were – under ordinary circumstances – in a fit state to be worked (areas where a normally safe atmosphere could not be ensured were to be fenced off "as far as possible"): it also required safety lamps to be examined and securely locked by a duly authorised person before use. Even when new and clean, illumination from the safety lamps was very poor, and the problem was not fully resolved until electric lamps became widely available in the late 19th century.

A modern day equivalent of the Davy lamp has been used in the Olympic flame torch relays. It was used in the relays for the Sydney, Athens, Turin, Beijing, Vancouver and Singapore Youth Olympic Games. It was also used for the Special Olympics Shanghai, Pan American and Central African games and for the London 2012 Summer Olympics relay. The National Mining Museum Scotland at Newtongrange, Scotland, also celebrated the 200th anniversary of the invention. In 2016, the Royal Institution of Great Britain, where the Davy lamp prototype is displayed, decided to have the invention 3D scanned, reverse engineered and presented to the museum visitors in a more accessible digital format via a virtual reality cabinet. At first sight it appears to be a traditional display cabinet but has a touch screen with various options for visitors to view and reference the virtual exhibits inside.