The deeper seams contained a dangerous gas called 'fire-damp' which could be exploded by the miners' candles. The safety lamp, which was invented in the early nineteenth century, did not really solve this problem, but it was often used to detect gas and so made the mining of deeper seams possible. There the air was more foul, the temperature higher (one pit paid the men an extra 6d a day for working in 130�F) and the risk of fire-damp even greater. In the 1840s a series of terrible explosions in the deeper mines led to stricter regulations, which inspectors helped enforce. The inspectors were particularly keen on proper ventilating machines and, although deeper shafts were sunk, they did not become more dangerous. However, many serious accidents still occurred.