SPAN GAS FOR MARINE GAS DETECTOR FASTCALGAS UN1956 Compressed gas , n.o.s ( Oxygen, Nitrogen Mixture) / Gas composition : Hydrogen sulphide 50 ppm , Carbon Monoxide 500 ppm, Methane 2.2%, Oxygen 18% , Nitorgen balance. Minor component(s) certified to be +/-5% C: 1.7 Contents: 1.7 Ltr, 8AL 500psi NA..NA.FCG21222