High or low temperatures

An excess of heat or deficit - cold - is termed thermal stress. Heat is exchanged between the body and the environment, using physiological processes. Environmental factors determining the level of heat stress include:

• air temperature;
• relative humidity;
• air movement; and
• radiant temperature of the surroundings

Heat stress is high in an environment characterised by high ambient temperatures, high humidity and low air movement such as in a sauna. Cold stress is associated with low temperature, high air movement and humidity, for example, from a blast of cold, wet wind.

Hot work induces heat stress when more heat is absorbed into the body than can be dissipated. The short-term effects of heat stress are to:

• reduce concentration and thus promote accidents;
• aggravate effects of other workplace hazards; and
• induce heat illness.

Heat illness manifests itself as skin conditions (prickly heat), as heat exhaustion (fainting, syncope), or as heat cramps (if body water and salt balance is incorrect). The long-term effects of heat stress include chronic heat exhaustion or birth deformities and other reproductive problems.

Our bodies are unable to acclimatize to cold in the same manner that they can adapt to heat. Lowering of body temperature (hypothermia) has an effect on the brain, causing erratic behaviour and numbness, muscular weakness and cramps. Localised exposure to cold may cause frostbite and chilblains.

Long-term effects of working in the cold include arthritis, rheumatism, chest complaints and heart disease, because of the strain on the heart caused by circulatory changes.

The range of thermal comfort for workers has been found to be 19 deg C to 30 deg C. Control of heat and cold should aim to lower or raise working temperatures to within this range. Measures available include:

• insulation;
• ventilation;
• heating;
• isolation;
• shielding of the source or the operator;
• job modification and work rotation; and
• protective clothing.