the heart beats harder and faster to maintain blood to the brain and other vital body organs. This effect is seen as an increase in both pulse (first sign) and blood pressure. Of course, when in protective clothing and equipment, the responder generates even more heat and eventually reaches a point when he/she can no longer work. Either he/she becomes simply too fatigued to continue, or he/she pushes himself/herself beyond the normal safe limits. In the excitement of the situation he/she may ignore his body's warnings of heat stress, and allow the core body temperature to become so high that brain function is impaired, or get so dehydrated that the heart cannot maintain adequate blood pressure to the brain, resulting in loss of consciousness. Obviously, either of these latter results could be deadly at a fire or HAZMAT scene.
Conforming to prescribed work/rest cycles in a HAZMAT operation is one way of avoiding the complications of heat stress, but this may be impractical while suppressing a fire. By training fire fighters to monitor their own pulse, and paramedics to measure both pulse and blood pressure, responders who are in acute danger of succumbing to the effects of heat and dehydration can be removed from the environment before they become heat casualties. In previous studies, physically fit workers have been able to work harder and longer before reaching a state of fatigue in a hot environment. Consequently, fit emergency responders, who are evaluated as described below should be able to work at HAZMAT and fire scenes while avoiding heat stress.
A.: The highest safe heart rate at each age for extended periods, which is calculated using the formula, 220-(age)= AAMHR.
B.: A term to describe significant dehydration based upon a criteria of an abnormal change in pulse or blood pressure after moving from prone to standing position. Compared to the levels when lying down, an increase in pulse of more than ten beats per minute, or a decrease in systolic blood pressure of more than ten mmHg, after standing for two minutes is indicative of orthostatic dehydration.
C. An index that expresses the combined effect of environmental temperature and humidity on the body. For example, with an environmental temperature of 90oF (32oC) and a relative humidity of 90%, the Apparent Temperature is 122oF (50°C). Thus, the fire fighter exposed to these conditions will experience discomfort similar to that associated with an environmental temperature of 122°F (50 C) at low humidity. ). Additionally exposure to direct sunlight as well as the use of protective clothing will each increase Apparent Temperature by about 10°F (2°C).