Common terms

There are important differences between the common terms of heat stress and heat strain.

Heat stress is the total heat load on the body from all sources including:

• ambient air temperature
• radiant heat from other sources (e.g. vehicles, equipment and hot-work processes)
• air movement
• relative humidity
• individual task requirements such as a need to wear a respirator or multiple layers of clothing
• metabolic heat produced by the body because of physical activity.

Heat strain is how the body responds to heat stress. These responses are focussed on removing heat from the body and are influenced by:

• physical fitness
• degree of acclimatisation
• medical conditions
• age
• general health
• weight
• hydration state
• certain drugs/medications.