<P> When surface supplied equipment is used the diver does not have the option of simply taking out the DV and switching to an independent system, and gas switching may be done during a dive, including use of pure oxygen for accelerated decompression . To reduce the risk of confusion or getting the system contaminated, surface supplied systems may be required to be oxygen clean for all services except straight air diving . </P> <P> Regulators to be used with pure oxygen and nitrox mixtures containing more than 40% oxygen by volume should use oxygen compatible components and lubricants, and be cleaned for oxygen service . </P> <P> Helium is an exceptionally nonreactive gas and breathing gases containing helium do not require any special cleaning or lubricants . However, as helium is generally used for deep dives, it will normally be used with high performance regulators, suitable for the depth . </P> <P> Invented in 1916 by Riichi Watanabi and the blacksmith Kinzo Ohgushi, and used with either surface supplied air or a 150 bar steel scuba cylinder holding 1000 litres free air, the valve supplied air to a mask over the diver's nose and eyes and the demand valve was operated by the diver's teeth . Gas flow was proportional to bite force and duration . The breathing apparatus was used successfully for fishing and salvage work and by the military Japanese Underwater Unit until the end of the Pacific War . </P>

How many and what type of air hoses run out of the first stage regulator unit