Anti-Heat Stress

The body defends itself from heat through three mechanisms: breathing, sweating, and changing the blood flow. The first reaction is to circulate blood to the skin, which increases skin temperature and allows the body to give off some heat.

How Your Body Reacts to Hot Conditions

Four environmental factors affect the amount of stress a worker faces in a hot work area: temperature, humidity, radiant heat (such as from the sun or a furnace) and wind speed. Individuals with high blood pressure or some heart conditions and those who take diuretics (water pills) may be more sensitive to heat exposure.

The body defends itself from heat through three mechanisms: breathing, sweating, and changing the blood flow. The first reaction is to circulate blood to the skin, which increases skin temperature and allows the body to give off some heat. During heavy work, muscles need more blood flow, which reduces the amount of blood available to flow to the skin and release the heat.

Sweating also helps the body to cool off, but only when the humidity levels are low enough to allow the sweat to evaporate. This allows water and salts lost through sweat to be replaced.. Working in hot conditions may pose special hazards to safety and health.

Heat Stress Disorders

When the body becomes overheated, a condition of heat stress exists. Heat stress can lead to a number of problems, including heat exhaustion, heat stroke, heat cramps, fainting, or heat rash. Many people confuse these disorders, but it is important to be able to recognise each one and know what to do when it happens.

Each of these heat stress disorders is described below.

Heat exhaustion

Although not the most serious health problem, heat exhaustion is the most common heat work related ailment. Heat exhaustion happens when a worker sweats a lot and does not drink enough fluids or take in enough salt or both. The simple way to describe the worker is wet, off colour and weak.

    Signs and symptoms:
  • Sweaty
  • Weak or tired, possibly giddy
  • Nausea
  • Normal or slightly higher body temperature
  • Off-colour, clammy skin (sometimes flushed)
    What to do:
  • Rest in a cool place
  • Drink an electrolyte solution, such as Hydro Work
  • Avoid caffeinated beverages such as colas, iced tea or coffee
  • In severe cases involving vomiting or fainting, call for medical assistance

Heat stroke

Heat stroke is the most serious health problem for people working in the heat, but is not very common. It is caused by the failure of the body to regulate its core temperature. Sweating stops and the body cannot get rid of excess heat. Victims will die unless they receive proper treatment promptly.

    Signs and symptoms:
  • Mental confusion, delirium, fainting, or seizures
  • Body temperature of 41.1°C or higher
  • Hot, dry skin, usually red or bluish in colour
    What to do:
  • Call for medical assistance immediately and request an ambulance
  • Move victim to a cool area
  • Soak the victim with cool water
  • Fan the victim vigorously to increase cooling

Heat cramps

Heat cramps are painful muscle spasms. They occur when a worker drinks a lot of water, but does not replace salts lost from sweating. Tired muscles – those used for performing the work – are usually the most likely to have the cramps.

    Signs and symptoms:
  • Cramping or spasms of muscles
  • May occur during or after the work
    What to do:
  • Drink an electrolyte solution, such as Hydro Work
  • If the cramps are severe or not relieved by drinking a Hydro Work, seek medical attention

Fainting (Heat Syncope)

Fainting usually happens to someone who is not used to working in the hot environment and simply stands around. Moving around, rather than standing still, will usually reduce the likelihood of fainting.

    Signs and symptoms:
  • Brief loss of consciousness
  • Sweaty skin, normal body temperature
  • No signs of heat stroke or heat exhaustion
    What to do:
  • Lie down in a cool place
  • Seek medical attention if not recovered after brief period of lying down

Heat rash

Heat rash, also called prickly heat, may occur in hot and humid environments where sweat cannot evaporate easily. When the rash covers a large area or if it becomes infected, it may become very uncomfortable. Resting in a cool place and allowing the skin to dry may prevent heat rash.

    Signs and symptoms:
  • Rash characterised by small pink or red bumps
  • Irritation or prickly sensation
  • Itching
    What to do:
  • Keep skin clean and dry to prevent infection
  • Wear loose cotton clothing
  • Cool baths and air conditioning are very helpful
  • Some over-the counter lotions may help ease pain and itching

Preventing Heat Stress

In most cases, heat stress can be prevented or, at least, the risk of developing heat stress can be reduced.


Before potential exposure to heat stress ensure that you are properly hydrated. To ensure optimal hydration, consume approximately 300ml of Hydro Work 20 minutes before possible exposure.

During potential exposure to heat stress it is extremely important, especially if your urine is dark yellow, to replace the fluids you lose from sweating – as much as one litre per hour may be necessary to ensure that the body temperature remains stable and optimises cardiac function. Continual hydration also assists in maintaining blood volume which allows for efficient delivery of oxygen to working muscles and reduces the incidence of muscular cramps. Water and/or Hydro Work are recommended. Since caffeine is a diuretic (makes you urinate more), beverage such as cola, iced tea and coffee should be avoided. Thirst is not a reliable sign that your body needs fluids. When doing heavy work, it is better to sip rather than gulp the liquids.

After exposure to potential heat stress, replenishing fluid volume and glycogen stores is critical for the recovery of many of the body’s processes. Using a drink that contains electrolytes such as Hydro Work, allows fluid volume to be conserved, while the inclusion of carbohydrates improves the rate of intestinal absorption of sodium and water and replenishes glycogen stores.


Wear loose-fitting, lightweight clothing, such as cotton, to allow sweat to evaporate. Light colours absorb less heat than dark colours. When working outside, wear a lightweight hat with a good brim to keep the sun off your head and face.


Employees and supervisors need to be trained to be able to detect early signs of heat stress. Employees must understand the need to replace fluids and salt loss from sweat and recognise the signs of dehydration, fainting, heat cramps, heat exhaustion, and heat stroke.

Supervisors should watch for signs of heat stress and allow workers to interrupt their work if they are extremely uncomfortable. Supervisors should also ensure that work schedules allow appropriate rest periods and ensure liquids are available. They should use appropriate engineering controls, personal protective equipment and work practices to reduce the risk of heat stress.

Temperature-Humidity Index

A useful guide to summertime comfort is the Temperature- Humidity Index (THI). This table gives an approximation of how most people react to heat and humidity. To use the table, find out the temperature and relative humidity of the work area. Start at the temperature listed on the left, and read across to the number under the relative humidity level (round up to the higher percentage). This number is the temperature-humidity index. The values are for people wearing the right amount of clothing doing light work, with very little wind.

The lightly highlighted area is uncomfortable for everyone. For moderate to heavy activity, workers should be concerned about heat stress and should alternate time spent working in the heat and time in cooler areas or light work. When the THI is in the darkly highlighted area, extreme caution is indicated. Workers should be encouraged to drink plenty of fluids and be on the lookout for signs of heat stress.

27–32 °C Caution — fatigue is possible with prolonged exposure and activity. Continuing activity could result in heat cramps
32–41 °C Extreme caution — heat cramps, and heat exhaustion are possible. Continuing activity could result in heat stroke
41–54 °C Danger — heat cramps, and heat exhaustion are likely; heat stroke is probable with continued activity
ver 54 °C Extreme danger — heat stroke is imminent