Manned evaluation of a diver heater using hydrogen catalytic reactions

The necessity for active diver heating during long duration, cold water diving operations is well established. A proof of concept study was conducted to evaluate the effectiveness of a prototype hydrogen catalytic heater to satisfy the thermal protection needs of up to six combat swimmers in long duration, cold water missions. Body weight, urinary output, and rectal and skin temperatures were measured in six U.S. Navy divers during 3 dives to ∼6 m for 6 hours in 1.7°C (35°F) water temperatures. Level of thermal comfort was reported subjectively at pre-defined intervals by the test subjects. The hydrogen catalytic heater was found to be capable of delivering 2 kilowatts of active heating to up to six divers by circulating warm water through closed-circuit tubesuits at flow rates of up to 2.8 litres per minute (0.75 gallon per minute) at suit delivery temperatures of approximately 38-39°C (100-102°F). This heating capacity was shown to be capable of doubling to 4 kilowatts by either increasing the hydrogen circuit levels between 1-2% (still below the combustible range of 4% hydrogen), or by increasing both the hydrogen and air injection rates into the heater assembly, thereby keeping the hydrogen diluted. The heater control system was shown to successfully maintain pre-set water delivery temperatures through a feedback control loop with the hydrogen injection valve. Test results suggest that while the hydrogen catalytic heater is fully capable of providing adequate levels of supplemental heating for 6 divers simultaneously, a redesign of commercial tubesuit will be necessary to provide thermal comfort to the divers´ hands and feet and to prevent a thermal short through the divers´ head.