Is it safe to use rubber O-rings with Nitrox?

Yes. Many divers are surprised to learn the SCUBA industry convention of using fluorocarbon elastomers (FKM or FPM, aka Viton o-rings) with Nitrox is not a matter of oxygen fire safety. The introduction of Nitrox in recreational diving included a recommendation to use FKM for seals in gas blending equipment whose wetted surfaces contact pure Oxygen. This was frequently confused with the very important safety requirement for oxygen cleanliness (i.e. the absence of readily combustible materials); creating a mistaken but widely held belief that Viton is also somehow related to safety of Nitrox for diving equipment such as SCUBA regulators and cylinder valves.

FKM is no more 'safe' in Nitrox diving applications than ordinary synthetic nitrile rubber (NBR aka Buna-N). While FKM has a slightly higher temperature of ignition at {~ 900°F | 500°C} than NBR at {~ 750°F | 400°C}, nearly any material can still serve as fuel in the kindling chain to an oxygen fire that will reach {~ 5000°F | 2700°C}. The reason for preferring FKM in high oxygen content applications is because the service life is typically longer than NBR, i.e. Viton is more resistant to oxidation than nitrile rubber although FKM also exhibits a tendency to swell slightly in high-pressure oxygen. While FKM o-rings theoretically outperform NBR o-rings, in practice there is no safety reason to prefer them in Nitrox SCUBA life-support applications such as regulators and valves given the periodic service requirements of such equipment.

Regardless, Dive Gear Express specifies oxygen compatible and oxygen clean products whenever possible, and we only use viton O-rings and O2 compatible lubricants in equipment service. Any products we identify as Nitrox Ready or Oxygen Service will meet industry standards for both oxygen compatibility and oxygen cleanliness prior to initial use.

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