Thermal Problems in Hyperbaric Environments

This paper reviews thermal problems in hyperbaric environments and provides information how to estimate thermal comfort zones in hyperbaric environments. Divers are exposed to hyperbaric helium-oxygen atmospheres when engaged in saturation diving operations. However, some difficulties to control thermal environments arise from the extremely high thermal conductivity of helium used as a breathing gas and from increased pressure. In order to obtain data available for control of thermal environments, many theoretical and empirical studies have been carried out to estimate heat exchange between man and his environments. For example, male divers wearing different clothing ensembles were exposed to six different pressures for evaluating change in clothing insulation. In addition, a lightly clothed male diver exercised on a bicycle ergometer while exposed to five different pressures to evaluate changes in clothing permeability. The results demonstrated that clothing insulation decreased with change in ambient gases and clothing permeability decreased slightly despite changes in ambient gas and barometric pressure. As represented by this example, in hyperbaric helium-oxygen atmospheres, the manner of heat exchange between man and his environments becomes apparently different from that in normobaric air. The last part of this paper demonstrates the comfort range of ambient temperatures at increased barometric pressures.