The quarries and mines made increasing use of mechanization from the start of the 20th century, with electricity replacing steam and water as a power source. The Llechwedd quarry introduced its first electrical plant in 1891, and in 1906, a hydro-electric plant was opened in Cwm Dyli, on the lower slopes of Snowdon, which supplied electricity to the largest quarries in the area. The use of electric saws and other machinery reduced the hard manual labour involved in extracting the slate, but produced much more slate dust than the old manual methods, leading to an increased incidence of silicosis. The work was also dangerous in other ways, with the blasting operations responsible for many deaths. A government enquiry in 1893 found that the death rate for underground workers in the slate mines was 3.23 per thousand, higher than the rate for coal miners.