Inside Boulby Potash Mine

BOULBY, UNITED KINGDOM - NOVEMBER 21: The door to a 'safe haven' room that offers emergency equipment and breathing apparatus in case of emergencies is lit by a green light 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)