Helium-oxygen gas mixtures conduct heat away from the diver very rapidly. As a
result, temperatures higher than those required in an air environment are necessary
to keep a diver comfortable. As depth increases, the temperature necessary to
achieve comfort may increase to the 85–93°F range.
As a general guideline to achieve optimum comfort for all divers, the temperature
should be kept low enough for the warmest diver to be comfortable. Cooler divers
can add clothing as needed. All divers should be questioned frequently about their
The relative humidity should be maintained between 30 and 80 percent with 50 to
70 percent being the most desirable range for diver comfort, carbon dioxide
scrubber performance, and fire protection.