Safety helmet for miners

A miner's safety helmet comprising:

• (a) inner and outer shells made of tough, hard impact resistant material having a generally hemispheric shape to conform to upper part of the wearer's head, the shells being spaced apart, closed around the rims thereof to form an enclosed space therebetween, and shaped around the rims such that when positioned on the wearer's head, the wearer's ears are left uncovered,
• (b) a slot like opening at the front part of the rim of the helmet into the enclosed space,
• (c) a visor of transparent plastic material retractably and telescopically mounted in the slot and having a doubly curved shape to conform with the shape of the enclosed space such that when the visor is in a fully retracted position it lies almost completely in the enclosed space and when in fully extended position it extends over the face of the wearer,
• (d) a source of clean filtered air,
• (e) an air supply connection at the rear of the helmet connected to said source of clean filtered air, said air supply connection connected to the enclosed space between inner and outer shells,
• (f) switch means mounted in the helmet in the enclosed space and operatively disposed in relation to the visor configuration, and
• (g) means connected between the switch means and the air source, such that when the visor is in an extended position the switch is operative to turn on the air source to provide a flow of air down over the wearer's face inside the visor and when the visor is in partially or fully retracted position the switch is operative to turn off the air supply.