OCC 12
FWIW, candles were used in mines from the 13th century at least to detect bad air (flame would gutter or even go out if there wasn't enough oxygen) or dangerous gases (it would take on a blue mantle with high levels of carbon monoxide or methane). After its invention in 1815, a Davey lamp, with the flame enclosed in a fine metal mesh, would give the same indications without the risk of igniting high concentrations of methane and causing an explosion.