I remember learning about the Davy Lamp at school. Twice, in fact. Once in primary school, where we learned about wonderful inventions that benefited the human race, and once in secondary school, as part of a physics lesson about oxygen and flame propagation.
The Davy Lamp was invented in 1815 by Sir Humphry Davy. In 1812, there was an explosion of flammable gas in a mine at Felling, near Newcastle-upon-Tyne. A miner's candle ignited a pocket of methane, which caused an explosion in the coal dust present in the mine's atmosphere, which blasted through the galleries and erupted through the main shaft to the surface. 91 miners lost their lives. One of the things most feared by miners in the early days was 'damp' - gases in the air of the mine which were both undetectable and deadly. The main two were firedamp, which was basically methane and was highly flammable, and blackdamp, which was mostly carbon dioxide and was suffocating.
Davy was a chemist (he discovered both chlorine and iodine), but was also an amateur inventor. He started a series of experiments to see if a naked light could be shrouded so that oxygen could still reach the flame, but the flame could not ignite any surrounding gases. The lamp which bears his name had a naked flame over a reservoir of vegetable oil, and the flame was contained in a gauze tube. The holes in the gauze were big enough to let in oxygen and methane, but would not let the flame propagate outwards.
The lamp worked very well. In the presence of methane, the flame would rise up in the lamp and develop a blue tinge. This would alert the miners to the presence of firedamp and allow them to avoid it or take corrective action, and also would give them light to work without the risk of explosion. Placed on the floor, where blackdamp accumulates, the flame would go out if the oxygen level went below 17%, which indicates the presence of Co2 but will still support life, allowing the miners to escape before the atmosphere became deadly. Although fragile, the lamp worked well and should have been a major factor in improving mine safety.
Except it wasn't.
After the introduction of the Davy Lamp, mine accidents increased. The lamp (which had to be bought by the miners themselves from the same company stores where they used to buy their over-priced candles) allowed mining in mines that had previously been closed for safety reasons. Also, methane itself is not toxic, so the presence of the Davy Lamp allowed mining to continue in places where firedamp was present. One spark from a metal pick or a hobnail, or one strand of the gauze rusting away from the shroud on the lamp, or a clumsy fall allowing the lamp to spill onto the floor - and another explosion occurred.
Mine explosions following the introduction of the Davy Lamp (numbers killed in brackets):
- Oaks Colliery 1866 (388)
- Wood Pit, Haydock 1878 (189+)
- Trimdon Grange 1882 (69)
- Hulton Colliery 1910 (344)