Ordinarily the body remains at a fairly constant temperature of 98.6F. It is very important that this body temperature be main-tained and, since there is a continuous heat gain from internal body processes, there must also be a continuous loss to maintain body heat in balance. Excess heat must be absorbed by the surrounding air or lost by radiation. As the temperature and humidity of the environment vary, the human body automatically regulates the amount of heat it gives off. However, the bodys ability to adjust to varying environmental conditions is limited. Furthermore, although the body may adjust to a certain (limited) range of atmospheric conditions, it does so with a distinct feeling of discomfort. The following discussion will help you understand how atmospheric conditions affect the bodys ability to maintain a heat balance.

Body Heat Gains

The human body gains heat (1) by radiation, (2) by convection, (3) by conduction, and (4) as a by-product of the physiological processes that take place within the body (for example, the conversion of food into energy). Heat gain from radiation comes from our surroundings. However, heat always travels from areas of higher temperature to areas of lower temperature. Therefore, the human body receives heat from those surroundings that have a temperature higher than body surface temperature. The greatest source of heat radiation is the sun. Some sources of indoor heat radiation are heating devices, operating machinery, and hot steam piping. Heat gain from convection comes only from currents of heated air. Such currents of air may come from a galley stove or an operating diesel engine.

Heat gain from conduction comes from objects with which the body comes in con-tact. Most body heat comes from within the body itself. Heat is produced continuously inside the body by the oxidation of food, by other chemical processes, and by friction and tension within muscle tissues.

Body Heat Losses

There are two types of body heat losses: loss of sensible heat and loss of latent heat. Sensible heat is given off by (1) radiation, (2) convection, and (3) conduction. Latent heat is given off in the breath and by evapora-tion of perspiration.