This is the most dangerous form of heat stress with complete failure of the body's ability to cool itself. Signs include extremely elevated body temperature, hot, dry, and red skin, disorientation to unconsciousness, and muscle spasms to convulsions. Treatment includes rapid fluid replacement including IV's, cooling, and transport to the hospital.
Recognition of each stage of heat stress can prevent a dire emergency from occurring. Proper response can avert a bigger problem later.
It is also important to monitor the weather and keep an eye on heat stress conditions. Particularly, weather with high temperatures along with high humidity increases the cooling load on the body. Dew points, the temperature at which atmospheric water condenses, above 70F are very humid days that should activate aggressive personnel cooling techniques.
Weather conditions above 80F and 40% humidity make the apparent temperature feel warmer. For this reason heat indexes have been developed to better indicate the heat load on a human. These charts are available from many sources and they should be accessed by responders to better monitor heat stress to personnel.
Probably the best method of controlling heat stress is through prevention measures. The following are some methods that can be employed to avoid heat stress problems.
1. Personal Conditioning.
A physically fit person can tolerate heat stress better than a person who does not exercise and eat properly. In short the physically fit have better circulatory systems and can dissipate heat better.
To help ensure only medically fit personnel are allowed on-duty for firefighting many departments have mandatory medical monitoring programs. The National Fire Protection Association Standard for Fire Department Health and Safety Programs (NFPA 1500) recommends annual physical exams for all firefighters. The exams include several tests that provide a basis for good health and should assist personnel in heat tolerance. Additionally, all personnel who belong to a hazmat response teams are mandated by federal law to participate in a annual medical monitoring program.
On-scene Medical Monitoring
Even though no federal mandates or national standards exist to do so many hazmat response teams conduct pre-entry medical monitoring for entry personnel at each emergency. These screenings are designed to determine if personnel are fit for duty in chemical clothing. (Since these screenings contain medical information they must remain confidential between the medical care-giver and the entry person.) The medical care-giver makes a determination as to whether an entry person is fit to wear chemical clothing usually based on accepted guidelines. These guidelines would preclude entry or the wearing of chemical clothing by any person if values are above the following:
Source; National Fire Academy (NFA) Hazardous Materials Site Practices, Hazardous Materials Strategies and Tactics by David M. Lesak
Also, all personnel need to be medically evaluated after work missions using the same parameters as above and this is when heat stress problems need to be aggressively corrected. Additionally, many hazmat response teams check for weight loss and EKG's to monitor personnel. The EKG interpretation is at the discretion of HazMat EMS and the guideline for weight loss should not exceed 1.5% body weight of an individual. Finally, personnel who are actively taking antihistamines such as Actifed or Benadryl may have an impaired ability to sweat and may not be suited for entry in chemical clothing. It is the responsibility of the entry person to inform medical control with this information.
In order to endure heat it is recommended to be in the heat for prolonged periods to get "used" to it. The human body adapts to its environment in a short period of time and heat adaptation is no exception. So, rather than remain indoors during hot weather it behooves responders to endure the hot weather conditions, at least for short durations, to better adapt. A heat acclimated responder is less prone to encounter heat related problems.
3. Pace Reduction