Table 1 Properties of commonly used diving gases
Compressed airCheap and readily availableNitrogen narcosis below 30 mswDensity increases work of breathing below 50 mswMost common breathing mixture for recreational diving
100% oxygenMinimal narcotic potencyCNS oxygen toxicity above 2 barMilitary and experimental diversDecompression gas in technical diversLimited to depths of 6–8 msw
Nitrox(nitrogen–oxygen,nitrogen <80%)Increased dive timeReduced decompression timePotential for oxygen toxicity if inappropriate mixture used at depthTechnical recreational divingDecompression gas for technical divers
Heliox(helium–oxygen)Reduced narcosisReduced densityHigh thermal conductivitySpeech distortionHigh pressure neurological syndrome beneath 200 mswCostTaste lossCommercial diving >50 mswMilitary divingTechnical recreational diving
Trimix(helium–nitrogen–oxygen)Reduced narcosisReduced densityReduced high pressure neurological syndrome risk on deep divingAvoid hyperoxiaCostComplicated mixing and risk of errorDeep commercial divingDeep technical recreational diving
  • CNS, central nervous system; msw, metres of sea water.