MIL-PRF-27407 Revision D, August 1, 2014
PROPELLANT PRESSURIZING AGENT, HELIUM
Type I, Grade A, helium is intended for pressurization of military rocket engine propellant systems, space vehicles and associated ground support equipment, welding and other shielding gas operations. Type I, Grade B, helium is intended for use (when blended with oxygen) as a respirable breathing gas for divers during deep excursions into the oceans. Type II helium is intended for use as a cryogenic coolant in specialized test and measurement equipment.