Safety First: How the body physiologically responds to heat, heat illness

  • Published
  • By 1st Lt. Pierre Nelson and Capt. Daniel Baseley
  • 461st Aerospace and Operational Physiology and 78th Bioenvironmental Engineering Flight
ROBINS AIR FORCE BASE, Ga. --  Georgia summers are brutal. Between the high temperatures and humidity it can seem almost unbearable.

That's why it's so important for those who live and work here to understand how the body responds to hot weather. 

When the body's thermoregulatory center senses a rising core temperature, certain functions begin to take place. As body temperatures increase, also known as hyperthermia, the body struggles to maintain a constant core temperature. 

Generally, human performance is impaired above 100 degrees Fahrenheit. That leads to various symptoms like short-term memory loss, an increase in error rate, erosion of motor skills and diminished insight into judgment skills - everything needed to increase the likelihood of a mishap occurring. 

The following are physiological stages of heat stress that need to be recognized:

HEAT CRAMPS
Heat cramps occur when the body temperature reaches 99.5 to 100.5 F. Symptoms include painful muscle cramps of the extremities and abdomen. 

Treatment consists of resting, getting out of the heat and into shade, and forcing as many fluids as can be tolerated. Sports drinks with electrolytes might be helpful, but water is essential.

HEAT EXHAUSTION
The body temperature of heat exhaustion is 101 to 105 F. It's the first stage where the body is unable to keep up with controlling the core temperature. The thermoregulatory center is still working, but the cardiovascular system is working harder to keep up with the increased heart rate necessary to overcome the dilated vessels during the transport of heat from blood flow. 

Symptoms include headache, confusion, loss of appetite, nausea and cramps. Treatment consists of resting in the shade or in a cooler setting. Fluids are important, and water is all that is needed at this stage. Don't be overly concerned with salt replacement.

HEAT STROKE
The last phase of inadequate temperature control is the most serious and occurs when body temperature rises above 105 F. This is a medical emergency when identified. The body is no longer capable of defending itself. The body's thermoregulatory center has broken down and is unable to manage the body's temperature control functions.

Symptoms include headache, confusion, dizziness, weakness and often nearly a coma. Sweat is no longer being made; therefore, no evaporation is taking place. The first step towards treatment is to get this person to a cool place and off hot surfaces. Call for medical help immediately and spray or pour liquid over the body to help cooling. It will be difficult to get the victim to drink because there is confusion and early unconsciousness.

OCCUPATIONAL AND ENVIRONMENTAL MONITORING
An assessment of the environmental conditions can be used to approximate the risk of thermal injury. During times of heightened temperature, the Bioenvironmental Engineering Flight measures the Wet Bulb Globe Temperature to make this assessment.

These measurements are communicated in the form of Flag Colors. AFI 48-151 gives guidance on recommended levels of fluid intake and work/rest cycles for each of the risk levels.

The outdoor WBGT is a calculation taking into account ambient temperature, humidity and solar load. Additionally, WBGT may be modified to take into account the increased risk due to personal protective equipment. Chemical protective equipment can increase the effective WBGT by 10 F for light work and 20 F for moderate to heavy work. Body armor adds an additional 5 F to the effective WBGT. This can change an individual's risk of thermal injury from low to high.

The WBGT notifications and recommendations are no replacement for education, training and awareness. Individuals should stay alert to their condition and to the condition of their wingmen. Remember, it is easier to prevent heat illness from happening than to try to treat it once symptoms develop.


Editor's Note: For more information on thermal stress prevention, contact the local human performance training team at DSN 241-5048.  For more information on WBGT, contact the Bioenvironmental Engineering Flight at DSN   497-7555.