Heat is the leading cause of death among weather-related phenomena, and is becoming more dangerous as 18 of the last 19 years were the hottest on record, states the Occupational Safety and Health Administration (OSHA). Increasing temperatures have put those who work outside at greater risk of heat related illness and injury (see article).
Military personnel are at high risk for heat illness, especially during rigorous physical outdoor training. Because of the added heat stress from the body during vigorous activity, the military refers to heat-related medical conditions as ‘exertional heat illness’ or EHI. The amount of time exposed and number consecutive days of strenuous activities in high heat increases the risk of an EHI.
High heat is a primary EHI hazard, so most EHIs occur between May and September, especially when the outside temperature is over 75° Fahrenheit (F). But temperature is not the only factor – sunlight, humidity, and wind speed affect heat illness risk. The military uses the Wet Bulb Globe Temperature (WBGT) index to combine these into one value and provides operational risk levels based on WGBT. Some installations are at higher risk than others due to routinely high WGBT, but WGBT varies throughout the day and can be quite different in different locations on an installation, so the WBGT should be taken at the time and location of an activity to assess risk.
Individuals may also have factors that increase their susceptibility to heat illness. For example, having a heat illness one time (heat cramps, heat exhaustion, heat stroke) increases a person’s susceptibility to future heat-related illness – even one that is more severe. Certain health conditions, fitness level, medications, nutrition and hydration are examples of other factors that can influence individual risk levels of EHI.
See the DCPH-A Heat Illness Prevention Guide for Service Members as a quick reference to reduce risk of EHI. This guide is based on the 2022 major update to
TB Med 507, the Army’s heat casualty prevention doctrine manual.
- DCPH-A is in process of updating other heat products. If you have questions please Contact Us
Exertional Heat Illness
Exertional heat illnesses (EHI) refers to conditions that can occur when your body overheats, ranging from dehydration and mild heat cramps, to a more serious medical condition called heat exhaustion, to the life-threatening medical emergencies heat stroke and hyponatremia (a condition when excessive water consumption causes an imbalance to the body’s chemistry).
Failure to prevent milder conditions from progressing can result in more serious heat casualties, including death.
Click banner to learn about the types of heat illnesses
Heat Illness Impacts Readiness
Heat illness, and dehydration from vigorous activity in heat, is a threat to individual health and to military operational success. Some supporting facts:
- Since 2014, more than 1,500 Soldiers each year have developed a heat illness that required medical attention and/or lost duty time
- Heat illnesses were responsible for more than 20,500 lost/limited duty days in 2017
- Losing as much as 4% of body weight from dehydration can degrade physical performance
- Every 1% loss of body weight increases core temperature (0.10-0.23⁰C or 0.18-0.40⁰F), thereby increasing risk of a more serious heat illness
Army Heat Illness Factsheet
Click banner to view Exertional Heat Illness video on YouTube
Link to video on milTube, with captions (CAC required)
Click banner to view DCPH-A Heat Related Injury Reports
The most severe types of heat illness (heat stroke and heat exhaustion) are military Reportable Medical Events (RME) and are routinely reported.