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Occupational Health and Safety Information Sheet - Thermal Comfort and Heat

Occupational Health and Safety Issues - Information Sheet No. 11

Background

Thermal comfort can be defined as: "that condition of mind which expresses satisfaction with the thermal environment". Each person is the expert on their own thermal comfort. A person's perception of thermal comfort is affected by air temperature, air movement (speed), humidity, clothing, activity level (ie the amount of physical work done), mean radiant temperature (the average temperature of the walls, floor windows, etc) and many other factors. However, the four most important environmental factors contributing to thermal comfort are air temperature, humidity, mean radiant temperature and air speed.

There is a significant difference between thermal discomfort and heat stress. Heat stress occurs in situations where a person's core temperature rises above 38 oC. Body temperature is regulated by the blood flowing from the core (abdomen, heart, brain) to the skin where the heat is dissipated by radiation, convection and evaporation to the environment. Heat stress may occur in
environments where there is a combination of two or more of the following:

  • high temperature (eg summer);
  • high thermal radiation (eg foundries);
  • high humidity (eg mines);
  • a high level of activity (eg manual labour);
  • excessive or impervious clothing.

Under these conditions heat loss may no longer be in balance with heat production and heat related illness such as heat cramps, heat exhaustion, heat stroke may occur. There are very few work environments at Monash University that could give rise to heat stress.

There is no legislation that specifies maximum temperatures in the workplace.

Factors Affecting Thermal Comfort

The effect of air temperature

Air temperature is the most important factor contributing to thermal comfort. There is no scientifically correct "best" temperature. The best temperature is the temperature that most people find comfortable. The most important point is that it is impossible to please everybody. The best temperature depends on clothing worn and the type of work being performed. For general office work it has been found that 20 - 24 oC is comfortable for most people in winter, when winter clothes are being worn and 23° - 26°C in summer, when summer clothes are being worn.

The effect of mean radiant temperature

Mean radiant temperature is the average temperature of surfaces that surround a person. Sunlight coming in through a window will markedly contribute to mean radiant temperature. This may be decreased by simple measures such as the closing of blinds and curtains or the installation of solar film.

The effect of air speed

Air speed is the speed of movement of air in a working environment. If the air speed is too high it may cause discomfort and a sensation of draughtiness. There is no particular air speed for thermal comfort. Increased air speed will aid the evaporation of sweat thus leading to a cooling effect, particularly if loose clothing is worn. However, if the temperature or humidity is too high it cannot be compensated for by air speed.

The effect of humidity

Humidity is the amount of moisture in the air. For people who perform very light or sedentary activities the influence of humidity on personal comfort is not great. Higher humidity will make a person feel warmer particularly in a ventilated area where the air speed is low. In areas of very low humidity people may experience discomfort from dry eyes, nose and throat. Generally people are much more sensitive to extremes of temperature than extremes of humidity.

Possible Health Effects

There are no known health effects from thermal discomfort. However, extremes in air temperature may have adverse effects on productivity and job efficiency due to slower work rates, increased numbers of errors and absenteeism. People who are pregnant, overweight, unfit, dehydrated or unwell will tend to feel the heat more.

Recommendations

  • Wear the loosest possible clothing;
  • Ensure that clothing is sufficient to prevent sunburn if working outdoors;
  • Drink cool water frequently even if you are not thirsty;
  • Try to increase air movement, to allow evaporation of sweat, by opening windows and doors or using mechanical aids such as fans and air conditioners;
  • Use blinds, curtains and solar film to decrease radiant heat;
  • Job rotate or take frequent rest breaks.

Under Section 21 of theOccupational health and safety Act 2004: Duties of employers; part (1) "An employer shall provide and maintain so far as is practicable for employees a working environment that is safe and without risks to health". If productivity is low and distress levels are high due to thermal discomfort, then it is quite acceptable from a health and safety viewpoint for managers to send staff home. Thermal discomfort complaints are usually associated with a room temperature of 35°C and above.

For additional information, contact Occupational Health and Safety on:

November 1999