Closed respiration-ventilation system for use with high altitude full pressure garment.

I N order to appreciate the advantages of the closed respirationventilation system .over the open system, we should perhaps review the mechanics of both and discuss their respeotive advantages and disadvantages. In the open system, the helmet is separated from the rest of the su'it by a neck seal. Pressurization and oxygen concentration for this. area are controlled by a pressure regulator which delivers 100 ,per cent dry oxygen gas to the helmet automatically at the correct pressure for the ambient altitude. The suit is pressurized by ,the ventilation air which flows at a rate of from 1 to 10 cubic feet per minute (cfm) as selected by the user. The suit regulator automatically maintains the correct pressure in the suit for the ambient altitude by control of the suit ven,tilation air exhau's.t. In normal use, a constant flow ,of oxygen and air is exhausted from the suit. The wearer breathes oxygen and exhales it throngh a valve into the suit proper, where it exits with the ven,tilation air through the suit ventilation air exhaust port. The open system requires an oxygen system which will automatically provide 'the ,helmet with abont ,1.0 elm of 100 per cent oxygen gas at the