A safety lamp is any of several types of lamp that provides illumination in places such as coal mines where the air may carry coal dust or a build-up of flammable gases, which may explode if ignited, possibly by an electric spark. Until the development of effective electric lamps in the early 1900s, miners used flame lamps to provide illumination. Open flame lamps could ignite flammable gases which collected in mines, causing explosions; safety lamps were developed to enclose the flame to prevent it from igniting the explosive gases. Flame safety lamps have been replaced for lighting in mining with sealed explosion-proof electric lights, but continue to be used to detect gases.
Background
Damps or gases Miners have traditionally referred to the various gases encountered during mining as damps, from the Middle Low German word dampf (meaning "vapour"). Damps are variable mixtures and are historic terms.
Firedamp – Naturally occurring flammable mixtures, principally methane. Blackdamp or chokedamp – Nitrogen and carbon dioxide mixture with no oxygen. Formed by complete combustion of firedamp or occurring naturally. Coal in contact with air will oxidize slowly and, if unused workings are not ventilated, pockets of blackdamp may develop. Also referred to as azotic air in some 19th-century papers. Whitedamp – Formed by the incomplete combustion of coal, or firedamp. The mixture may contain significant amounts of carbon monoxide, which is toxic and potentially explosive. Stinkdamp – Naturally occurring hydrogen sulphide and other gases. The hydrogen sulphide is highly toxic, but easily detected by smell. The other gases with it may be firedamp or blackdamp. Afterdamp – The gas from an explosion of firedamp or coal dust. Contains varying proportions of blackdamp and whitedamp and is therefore suffocating, toxic, explosive, or any combination of these. Afterdamp may also contain stinkdamp. Afterdamp may be more dangerous following an explosion than the explosion itself.
Open-flame illumination Before the invention of safety lamps, miners used candles with open flames. This gave rise to frequent explosions. For example, at one colliery (Killingworth) in the north east of England, 10 miners were killed in 1806 and 12 in 1809. In 1812, 90 men and boys were suffocated or burnt to death in the Felling Pit near Gateshead and 22 in the following year. Wood 1853 describes the testing of a mine for firedamp. A candle is prepared by being trimmed and excess fat removed. It is held at arm's length at floor level in one hand, the other hand shielding out all except the tip of the flame. As the candle is raised the tip is observed and if unchanged the atmosphere is safe. If however the tip turns bluish-gray increasing in height to a thin extended point becoming a deeper blue, then firedamp is present. Upon detecting firedamp the candle is lowered and arrangements made for the ventilating of the area or the deliberate firing of the firedamp after the end of a shift. To fire the gas, a man edged forward with a lit candle on the end of a stick. He kept his head down to allow the explosion to pass over him, but as soon as the explosion had occurred stood as upright as possible to avoid the afterdamp. Officially known as a fireman, he was also referred to as a penitent or monk from the hooded garb he wore as protection. The protective clothing was made of well-dampened wool or leather. This was a job with risk of injury, or to life. When they came into regular use, barometers were used to tell if atmospheric pressure was low, which could lead to more firedamp seeping out of the coal seams into the mine galleries. This continued to be essential information even after the introduction of safety lamps; at Trimdon Grange there was an accident involving pressure. The lack of good lighting was a major cause of the eye affliction nystagmus. Miners working in thin seams or when undercutting the coal had to lie on their side in cramped conditions. The pick was swung horizontally to a point beyond the top of their head. In order to see where they were aiming (and accurate blows were needed), the eyes needed to be straining in what would normally be the upwards and slightly to one side direction. This straining led first to temporary nystagmus and then to a permanent disability. Mild nystagmus would self-correct if a miner ceased to perform this work, but if left untreated would force a man to give up mining. The lower levels of light emitted by safety lamps caused an increase in the incidence of nystagmus.
First attempts at safe lamps
In Europe and Britain dried fish skins which emitted a faint bioluminescence (often called phosphorescence) were used. Flint and steel mills introduced by Carlisle Spedding (1696–1755) before 1733 had been tried with limited success. An example of a Spedding steel mill may be seen in the museum at Whitehaven where Spedding was manager of the collieries of Sir James Lowther, 4th Baronet. A steel disk was rotated at high speed by a crank mechanism. Pressing a flint against the disk produced a shower of sparks and dim illumination. These mills were troublesome to use and were often worked by a boy, whose only task was to provide light for a group of miners. It was assumed that the sparks had insufficient energy to ignite firedamp until a series of explosions at Wallsend colliery in 1784; a further explosion in June 1785, which the operator of the mill survived, showed that ignition was possible. The first safety lamp made by William Reid Clanny used a pair of bellows to pump air through water to a candle burning in a metal case with a glass window. Exhaust gases passed out through water. The lamp was intrinsically safe provided it was kept upright, but gave out only a weak light. It was heavy and ungainly and required a man to pump it continuously. It was not a practical success, and Clanny subsequently changed the basis of operation of later lamps in the light of the Davy and Stephenson lamps.
Oil lamps
Principles of operation Safety lamps have to address the following issues:
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