Hyperthermia - Prevention

Prevention

When ambient temperature is excessive, humans and many animals cool themselves below ambient by evaporative cooling of sweat (or other aqueous liquid; saliva in dogs, for example); this helps to prevent potentially fatal hyperthermia. The effectiveness of evaporative cooling depends upon humidity; wet-bulb temperature, which takes account of humidity, or more complex calculated quantities such as Wet Bulb Globe Temperature (WGBT) which also takes account of solar radiation, give useful indications of the degree of heat stress, and are used by several agencies as the basis for heat stress prevention guidelines. (Wet-bulb temperature is essentially the lowest skin temperature attainable by evaporative cooling at a given ambient temperature and humidity.)

A sustained wet-bulb temperature exceeding 35 °C is likely to be fatal even to fit and healthy people, unclothed in the shade next to a fan; at this temperature, environmental heat gain instead of loss occurs. As of 2012 wet-bulb temperatures only very rarely exceeded 30 °C anywhere, although significant global warming may change this.

In cases of heat stress caused by physical exertion, hot environments or protective equipment, prevention or mitigation by frequent rest breaks, careful hydration and monitoring body temperature, should be attempted. However, in situations demanding prolonged exposure to a hot environment or wearing protective equipment, a personal cooling system is required as a matter of health and safety. A variety of active or passive, personal, cooling systems exist which can be categorized by their power sources and whether they are man or vehicle-mounted.

Due to the broad variety of operating conditions, a these devices must meet specific requirements, such as rate and duration of cooling, need for physical mobility and autonomy, access to power, and conformance with health & safety regulations. For example, active liquid systems operate on the basis of chilling water and circulating it through a garment that cools the skin surface area that it covers through conduction. This type of system has proven successful in certain Military, Law Enforcement and Industrial applications. Bomb disposal technicians wearing bomb suits to protect against an Improvised Explosive Device (IED) use a small, ice-based chiller unit strapped to their leg with a Liquid Circulating Garment, usually a vest, worn over their torso to maintain their core temperature at safe levels. By contrast, soldiers traveling in combat vehicles can face microclimate temperatures in excess of 65 °C and require a multiple-user vehicle-powered cooling system with rapid connection capabilities. Requirements for Hazmat teams, the medical community and workers in heavy-industry will vary further.