Protective clothing: heat exchange and physiological objectives

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Abstract
For a worker to maintain health, comfort and performance, internal body temperature should not vary greatly from an optimum of 37°C and skin temperature and sweat production should be at levels which do not produce discomfort. Clothing can protect workers from hazardous or unpleasant environments. Good clothing design will allow a microclimate enabling the body, within the clothing, to achieve desirable physiological objectives. The human thermoregulatory system and its relevance to the physiological objectives for clothing are considered, and a review of the heat transfer mechanisms between a worker and his/her environment is provided. Current thinking concerning the heat-balance equation for the clothed body and methods for describing the thermal properties of clothing are presented. This includes the TOG and CLO units, the Burton thermal efficiency factor, the Woodcock permeability index, the Nishi permeation efficiency factor and the work of Oohori el al. Recent work for ISO and ASHRAE is discussed. Practical methods for determining the thermal properties of clothing include the use of simple data bases, experiments with manikins and measurements on human subjects. It is concluded that while a great deal of progress has been made in the mathematical description of the heat exchange between a clothed man and his environment, there are still practical factors, often of overriding importance, which have not been described. Simple user performance trials and tests can provide a large amount of practical information about the thermal properties of clothing and are still necessary in many applications.