When the dive industry started compressing Nitrox, polyalphaolefin (PAO) synthetic lubricants became the de facto recommendation for lubricating Nitrox compressors. Mineral compressor oils can also have flash point temperatures above 200°C, so flash point alone does not distinguish the two lubricant types or establish their resistance to degradation and carbon monoxide formation in Nitrox service.
Today, PAO lubricant performance in compressors is surpassed by the synthetic ester based high-performance lubricants. Esters have a similar flash-point temperature range and, also like PAOs, there is no published data available as to how esters perform in Nitrox compressors. Lubrication professionals (called tribologists) we have consulted are of the opinion that if PAO lubricants are good with Nitrox then ester base lubricants are better; given their excellent performance in higher temperature applications with superior oxidation stability that resists formation of varnishes and carbon deposits.