Inside Boulby Potash Mine

BOULBY, UNITED KINGDOM - NOVEMBER 21: Tokens used to monitor the number of miners entering the mine hang on hooks at the Boulby Potash mine on November 21, 2014 in Boulby, United Kingdom. Cleveland Potash mine began production in 1973. At a depth of 1400 metres it is the second deepest mine in Europe and extends out 7 km under the North Sea. Each year the mine produces over a million tons of Potash and half a million tons of salt. It operates 365 days a year and employs around a thousand workers. Potash products are used for fertilizer production, as well as for glass making and applications in the chemical industry. The salt products also meet a variety of needs, from winter road maintenance to sugar beet cultivation and as an ingredient in animal feeds. (Photo by Ian Forsyth/Getty Images)