How is heat generated?

Heat stress comes from three sources:

  1. The environment – including the heat in the air, radiant heat from the sun or hot surfaces, and humidity. These are measured using the wet bulb globe temperature (WBGT).
  2. Clothing – the body’s ability to lose heat may be impaired by clothing, through adding insulation and decreasing the evaporation of sweat. For example, wearing body armour or Dress State 4 will impair the body’s ability to lose heat more than wearing AMCU or PT gear.
  3. Metabolic heat – the heat internally generated from metabolism. This internal or metabolic heat generation is small at rest, but increases exponentially with increases in work intensity. Internal heat production during running is more than double that of a slow walk. Carrying loads, such as a pack or weapon, will also increase internal heat production. Therefore it is critical to consider the work intensity and load carried when managing heat stress.

How do we respond to heat?

Once we start to work or exercise in the heat, our heart rate will increase to support oxygen delivery to our muscles, and divert blood to the skin to help lose heat. Our body temperature will begin to rise, triggering our body to sweat in order to prevent the continued increase in our core body temperature. However, at times, the level of heat stress coming from the environment, clothing and metabolism can be so severe that our body’s ability to cool itself is overwhelmed and our body temperature will continue to increase. This places considerable stress on our internal organs such as the heart and kidneys, and in some instances, can lead to early symptoms of heat stroke.

Key signs and symptoms of exertional heat illness

Exertional heat exhaustion

Exertional heat stroke


Persistent mental status changes


Personality changes


Inappropriate behaviour or aggression

Unsteady walk

High rectal temperature >40°C

Generalised weakness

Unsteady walk

Muscle cramps




Missing assigned tasks (cognitive function)


Feeling faint

Recurrent vomiting


Why do some people find it hard to cope with heat?

There can be varying individual responses to heat stress. Understanding the factors that may predispose you or your mates to exertional heat illness is important to help minimise risk of heat illness and injury.


Medications and Drugs

Health Conditions


Poor physical fitness

Overweight, high body mass index

Inadequate heat acclimatisation for current conditions

Heat stress in the previous 1-3 days


Age (infants, older adults)



B-adrenergic blockers



Stimulants (amphetamines, cocaine, ecstasy, ephedra)

Viral or bacterial infections


Diarrhoea or vomiting

Previous heat illness

Skin disorders (rash, large area of burned skin)

Diabetes mellitus

Cardiovascular disease

Self-imposed motivation to excel

Leadership or organisational structure

Peer or chain-of-command pressure to excel


What can you do to look after yourself and your mates?

  1. Before an activity:
    • Speak up if you are sick
    • Ensure you are hydrated
    • Acclimatise to heat
  2. During an activity:
    • Use the buddy system
    • Monitor for symptoms
    • Pace yourself
    • Stay hydrated
  3. After an activity:
    • Rehydrate
    • Rest and recover

First aid and cooling strategies

If heat illness and injury is suspected you must apply first aid using the acronym DRSABCD as taught in Army first aid. If heat illness is suspected, commence cooling and evacuate the person to medical support. You should also consider other medical causes (apart from heat) for their symptoms.

Initial treatment for exertional heat illness

Non-life threatening

  1. Stop work
  2. Rest in a cool location
  3. Rehydrate

Life threatening

  1. Stop work immediately and commence DRSABCD
  2. Notify chain of command immediately
  3. Remove clothing and equipment from casualty
  4. Start active cooling until medical help arrives
  5. Active cooling: These are listed in the order of effectiveness:
    • Immerse as much of the body in water as cold as possible.
    • Tip water repeatedly over the casualty. Putting a hootchie underneath to capture the water around casualty and fanning will help cooling.



Cooling strategies can be used during or after an activity to keep you cool. Some strategies are more effective than others at reducing your body temperature. A rough guide on effective cooling strategies is provided below. However, the most effective strategy will depend on the resources available and the environmental conditions. Combining two or more of the strategies may be more effective than one.

  • Fan use
  • Ice packs
  • Drinking cold water
  • Drinking a slushie
  • Move to a cooler area
  • Mist fan
  • Remove layers of clothing
  • Limb immersion
  • Body immersion
  • Cold shower