ABSTRACT
Humans are homeotherms, meaning that they attempt to control their deep body temperature within close limits in the face of wide variations in their activity and their environment. Maintenance of a relatively stable internal temperature allows the body’s enzymes, nerves and cell membranes to perform optimally. When the stresses of the environment exceed what the individual can cope with, the individual becomes susceptible to thermal strain, which may become manifest as an effect on their performance, or more extremely as a variety of heat or cold related illnesses or injuries. It is important to appreciate thermal issues in the context of aviation for a number of reasons. Thermal stress in the aircraft may have an adverse effect on aircrew performance and hence potentially affect flight safety or mission effectiveness. The ground crew who service the aircraft may have to work outdoors in hot or cold environments, and may be at risk from the effects of those environments. Finally, there is always the potential that a flight may suffer an emergency, and that the occupants may be faced with surviving in whatever environment the aircraft was flying over at the time; in these days of longdistance flights, that could potentially include cold-water, arctic, desert and jungle environments in a single flight. This chapter considers the fundamentals of how individuals exchange heat with their environment, and their physiological responses to thermal challenges. Chapter 12 more specifically considers the sources of thermal stress in the aviation environment, and the ways of potentially ameliorating its effects.
