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TOLERANCE TIME John H. Talbott Tolerance time is a very useful unit of measure in the studies pursued in the cold room. It may be applied to any item of clothing, handgear, footgear or sleeping gear. It is the capacity of an item to perform its function expressed in units of time. The term is comparable to the capacity of a gasoline stove to provide heat. When the gasoline in a stove lias been expended, the utility of the stove for the immediate purpose of supplying heat has passed temporarily and the tolerance time has been reached. The stove is still a useful item in that it has not been broken or damaged but some change in its state must be provided (supplying additional fuel) to restore its usefulness. In an item of clothing or other gear that provides thermal insulation, tolerance times have been used as the limit of usefulness under specified condi- tions. Woolen mittens with a windproof shell may be taken as an example. If a subject were to dress in a complete Arctic outfit with face mask and the best mukluks or felt shoes available and sit at rest without moving the hands at an exposure temperature of minus 40°F., in order to simulate duty on a look-out post, the hands would become uncomfortably cold within 30 or 45 minutes. After 60 minutes had passed the hands would become painful and by the end of 90 minutes some change in state must be provided otherwise the fingers will become frostbit- ten. It can be assumed that the tolerance time has been reached for the pair of mittens at the exposure temperature specified under the conditions of activity provided, which in this instance is rest. For the sake of emphasis it should be restated that the above-specified tolerance time of 90 minutes applies only to a subject at rest, wearing clothes as enumerated and at an exposure temperature of minus 40°F. If any one of these conditions is modified, tolerance time is altered. If the subject is simulating sentry duty and is slowly walking about, the breakdown point of the mitten becomes longer than 90 minutes, possibly 120 minutes. If the subject is engaged in physical activity, sufficiently strenuous to simulate a soldier in an engineer battalion building a bridge or a soldier pulling a sledge in the snow, the mitten may provide sufficient protection for several hours and the tolerance time will be increased to 4 or 6 hours. A second factor which increases tolerance time for a particular item is the insulation provided for the remainder of the body. The human body should be considered as a stove capable of generating considerable heat but the arms, legs and head are conducting the heat away faster than it can be produced. If the loss of heat through the feet can be reduced-, the covering over the remainder of the body including the hands remaining the same, the tolerance time for the mit- tens will be increased. The reverse is also true. It was stated that the subject in the cold room would wear the full Arctic assembly, a face mask and mukluks or felt boots. Instead of this footgear, let it be assumed that less adequate cover- ing were provided for the feet and that the subject wore service shoes and a pair of cloth overshoes. If this one item only, footgear, were altered other condi- tions being kept constant, the breakdown point in the hands would come in a shorter time than 90 minutes, possibly 70 minutes.
