Why do we get affected by heat stress? When we work, our metabolic rate increases and the temperature of our bodies’ organs and muscles rise (like a car engine where the waste heat starts to heat up the engine block and head). Our body begins to fatigue when deprived of important oxygen and nutrients, so it attempts to cool down the hot muscles and other body organs. When blood circulates through the body’s heat affected organs and muscles, it also heats up. The body has sensed the heat increase, so it pumps faster to distribute blood to the capillaries under the skin surface from where it sheds excess heat. It is cooled by the surrounding air and by sweating. (The skin is the body's radiator).

When we sweat we lose fluids (mostly water) from the blood. We need to keep drinking, topping up the fluids. You can lose up 2 or 3 litres of sweat per hour and over a full day that’s a lot of fluid to replace. If we do not drink enough, we lose too much fluid from the blood, and there will not be enough fluid for the heart to pump efficiently. Blood pressure drops and the body goes into what is called 'circulatory shock'. (In a car, the water pump does not get enough water to circulate through the engine and radiator, and the engine overheats).

The body tries to keep up the supply of blood to the vital organs (brain, heart and lungs). Unfortunately by diverting blood to the vital organs, blood flow to the skin is shut off and the body stops cooling itself. The temperature of the body increases, cells begin to break down, organs fail and death can result.

Preventing heat stress Managing and preventing heat stress in the work environment involves the following.

AWARENESS: Supervisors should regularly provide sound information to develop and maintain a heightened awareness of heat stress, so that both individuals and groups are alert and can respond quickly to the first symptoms of heat stress.

PREPARATION: Know how to prepare for work on hot days, and minimise personal risks by drinking and eating properly. Where possible, each day’s work should be planned to ensure the most strenuous activities are carried out in the cooler periods of the morning or afternoon.

MANAGEMENT: Strenuous work on hot days requires regular breaks to ensure people’s fluid levels are maintained (hydration) and body cooling occurs. Age, fitness and excess body mass will affect an individual’s capacity to work in the heat. Strenuous work in hot conditions needs to be shared, taking account of each individual’s capacity to work in hot conditions. Hard work may need to be rotated regularly.

RESPONSE: Be aware of the symptoms relating to heat stress. Employees should discuss heat stress openly and tell each other when they feel heat stress. They need to know how to respond quickly to symptoms.

REHYDRATION: Employees should drink cool water to replace lost fluids at least every 15 minutes, rest in a cool place to shed excess heat. A sound rule of thumb is to drink until you are no longer thirsty, and then drink one more cup. Thirst is a late indicator of dehydration and you may have already lost up to 2% of your body weight, so drink water before work, during work and after work.