Direct "In situ" measurement of thermal insulation quality underwater

Thermal insulation is one of the most critical components involved in life support in a large number of operations undersea. The degree to which thermal insulation is effective in blocking the flow of heat depends both upon its properties and also upon the environment. For example; the common closed cell wet-suit material compresses and loses efficiency as a function of pressure at depth. The factors involved in thermal protection of divers are very difficult to evaluate in theory or in the lab, thus a method of "in situ" measurement was developed. The method is based upon direct measurement of the heat flow through the thermal insulation by the use of thermoelectric heat flow transducers applied in series with the principal heat flow path. The temperature difference ( ) between the outer surface of the insulating layer and the skin is also determined and the thermal resistance is then computed as the ratio of /heat flow. Typical resistance units, readily convertible to "Clo", are . The feasibility of the method was tested at moderate depths in Catalina waters, with wetsuited divers, using open circuit SCUBA and "hooka" breathing systems. The instruments proved reliable. The thermal resistance, an indication of the functional quality of the wet suits, was measured for several suit configurations. Regional differences within a single suit as well as surface-averaged data for the whole suit were obtained. These data are reported as thermal resistance given as a function of location on the suit. The method would be equally applicable to the walls of habitats, or personnel transfer capsules, heated or passively insulated. The development of better thermal barriers for personnel protection undersea should be aided by this direct measurement method.