Active heating/cooling requirements for divers in water at varying temperatures

The active heating/cooling requirements to thermally sustain a human subject submerged in 10, 20, 30 and 40°C water was measured using a system that circulated water through a zoned tubesuit garment. Water at 30°C was circulated through the garment at a flow rate of about 0.5 L/min to each of six body regions and the outlet temperatures were measured. In addition, skin and core temperature, heat flux, and oxygen consumption was measured. The subject wore either a 6.5 mm or a 3 mm foam neoprene wetsuit. Body temperatures and heat fluxes reached steady state after 30-90 minutes and the immersions lasted 2-4 hours and core and skin temperatures remained within set thermal limits. In both wetsuits there was a linear correlation between the thermal exchange of the tubesuit and water temperature. While in the 6.5 mm wetsuit -214 to 242 W of heating (-) or cooling (+) was necessary in 10 to 40°C water, respectively. While wearing the 3 mm wetsuit -462 to 342 W was necessary in 10 to 40°C water, respectively. It was therefore concluded that a subject can be kept in thermal balance and comfort in 10-40°C water with active heating/cooling.