2828735 He-O2 helium-20% oxygen 13 2828741 He-O2 helium and 20% oxygen 5 2828744 He-O2 He-20% O2 4 2828743 He-O2 Helium (80%)-oxygen (20%) mixtures 1 2828742 He-O2 Helium-oxygen, He 79%-O2 21 1 2828740 He-O2 hyperbaric exposure of 20 atmospheres-absolute 1