When the temperature starts climbing into the thirties, we receive numerous calls from concerned employees and managers regarding what are "safe" levels of heat in which to work.  Unfortunately, although the question is easy to ask, the answers may be more complex.

ote that as heat discomfort in itself is not a health and safety illness, OHS law does not require heat discomfort to be addressed.

Heat Stress

Heat stress is not necessarily a medical condition - as long as the body copes with the levels of heat. However, if the heat levels become "too" high, the body needs to use its cooling mechanisms to prevent any adverse effects such as heat stroke.  The body can lose heat by:

• convection (heat loss to air) - this is the least important for the body; hot air rises and takes heat from the skin. Air movement, ventilation or wind enhances convection of heat away from the body.

• radiation (heat loss to surrounding objects) - heat is radiated from the body more or less continuously through the skin. However, if the ambient (surrounding) temperature exceeds 35ºC, the radiation mechanism does not work as the body is gaining heat from the surroundings.

• evaporation of perspiration (sweat) - This is the most important mechanism of heat loss.  As the water in perspiration (sweat) evaporates (ie turns to vapour), the skin is cooled. In very hot conditions, evaporation of perspiration may be the only means by which the body can maintain its temperature within the narrow range necessary for healthy functioning. The large amounts of fluid that can be lost by this mechanism must be replaced to prevent dehydration.

In the absence of an effective cooling mechanism, workers may suffer varying degrees of fatigue, heat exhaustion, heat cramp and heat stroke. The sweat evaporating / cooling mechanisms of workers who are not acclimatised to working in heat tend not to be as efficient s as those who are acclimatised. Thus, in hot conditions, workers should build up gradually to a full workload over a period of a week or so. 

The cooling systems of some people are not as efficient as others also needs to be considered:  people who are overweight, physically unfit, suffer from heart disease, alcohol abuse or take certain other medications are at greater risk of suffering adverse effects.

Heat Stroke

Some adverse effects (e.g. heat stroke) are very serious and must be regarded as medical emergencies. If a worker appears to be suffering from heat exhaustion, it is important to:

1. remove the worker from the heat and rest them in the coolest space available

2. encourage drinking cool (not cold) water

3. obtain medical or nursing assistance.

Symptoms of heat stroke include decreased sweating, high temperature, hot and dry skin, confusion and even loss of consciousness. Medical attention should be sought immediately for any worker with these symptoms. In the meantime first aid consisting of cooling the body by soaking the victims clothing and increasing air movement by fanning is desirable.

Heat Discomfort

Working conditions that cause heat illness can also cause heat discomfort. Heat discomfort is not a medical condition. It is the discomfort experienced by most people when it is hot - it's how we feel when it's hot. Most concerns that arise from working in heat are due to heat discomfort. In many cases, although we may feel considerable discomfort, the work conditions are such that we face no significant risk of the serious health and safety problem of heat illness. No matter what controls or procedures are implemented to decrease discomfort, at least 5% of employees in an area will always be dissatisfied with the thermal environment.

Assessing Heat Discomfort

First, establish if there is a significant risk of heat illness. If not, the heat discomfort issue can be addressed. 

Because heat discomfort is how an individual feels when it's hot, the assessment should include consultation with employees who are experiencing the discomfort. The use of thermal discomfort questionnaires can be useful for consulting large groups of employees. In other cases, direct discussion between management, employees and health and safety representatives may be better. The purpose of the consultation should be to establish the following:

• which employees are experiencing thermal discomfort

• when they are effected; e.g., particular times of the day, during particular weather conditions, etc

• the nature of the discomfort being experienced; e.g., just too hot, too humid, too sticky, too dry, too stuffy / stifling, 'no air circulation', etc

• what are regarded as the sources of the discomfort.

Inspect areas where thermal discomfort is being experienced to see if there are any obvious sources of discomfort, e.g., direct sunlight through windows, work areas with little or no ventilation, overcrowded work areas, faulty air conditioning or ventilation systems. Environmental measurements can also be undertaken. These can include air temperature, relative humidity and air movement. Generally comfortable conditions for people working indoors and doing light work (e.g. office work) are as follows:

• Air temperature (dry bulb temperature) 23º - 26ºC (an air temperature range 18º - 30ºC is considered acceptable)

• Relative humidity 30-60%.

Other more sophisticated assessments of heat discomfort are possible (eg using a Wet Bulb Globe Thermometer to find the WBGT index ).

Beating the Heat

Minimising the risk of heat illness occurring

The best way to minimise the risk of heat illness is to plan ahead - set up a "Heat Alert Program".  Management, in consultation with employees, should determine when and where a Heat Alert Program should to be implemented. (For example, in many Victorian workplaces a Heat Alert Program should be implemented every spring as the risk of heat illness occurs mainly during hot spells. In these situations, if the weather forecast predicts a hot spell, then a Heat Alert should be declared and measures put in place to prevent heat illness.)

In addition to basic control options such as changing work schedules to allow heavy work can be done during cooler times, other engineering controls to reduce heat exposure include:

• providing shade for outdoor work;

• shielding hot indoor sources that radiate heat (e.g., furnaces);

• enclosing the process and increasing ventilation to get rid of steam and hot air;

• increasing heat loss through sweating by reducing humidity, increasing air movement and wearing suitable clothing (e.g. loose fitting, light clothing).

Other elements of a Heat Alert Program could include:

• working at a sensible pace;

• getting more people to help with heavy or hot work

• providing opportunities for unacclimatised employees to acclimatise to working in heat;

• providing rest breaks in a cool, well-ventilated place

• drink a cup of clean cool palatable fluid, such as water, every 20 minutes or so

• rest in a cool well ventilated area and drink cool fluids if symptoms occur

• seek first aid if symptoms do not reduce rapidly.

Discuss these issues with all personnel.  Ensure they are aware of the issues, particularly the warning symptoms - encourage them to self monitor as they work.

Beating the Heat

Controlling heat discomfort

 Employers and employees should agree on procedures to resolve any heat discomfort issues. A range of options is available to address discomfort. Some of these are:

• fixing/improving faulty and/or inadequate ventilation and air conditioning systems

• providing fans and opening doors, windows and vents where practical

• wearing lighter and looser fitting clothing

• ensuring employees have free access to cool, palatable drinks. [Special 'sports' drinks and other electrolyte replacements are unnecessary; cool, clean water is sufficient.]

Further Information and Advice

Additional advice and information on hot working conditions and health and safety in general is available from Occupational Safety and Health Associates. 

Other publications about heat at work

1. National Health and Medical Research Council (Australia); Effects of heat on health, comfort and performance. 1986.

2. Victorian Code of Practise for Workplaces. (Copies may be purchased from Information Victoria).

3. The Wet Bulb Globe Temperature (WGBT) Index is described in: Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices; Published and updated annually by the American Conference of Governmental Industrial Hygienists.

4. IS07730 Moderate thermal environments - specification of the conditions for thermal comfort; International Standards Organisation.

Based on information in the publication "Working in Heat" on the website of the Victorian WorkCover Authority (2001) and the ACTU/VTHC Health and Safety Bulletin No 28 "Working in Heat" (1983). Occupational Safety & Health Associates (Aust) Pty Ltd believes that the advice and information herein are accurate and reliable, but no warranty of accuracy or reliability is given and no responsibility arising in any other way whatsoever for errors or omissions (including responsibility to any person by reason of negligence) is accepted by the Company or any officer or any employee of the Company. Neither the Company nor any officer or employee of the Company accepts any responsibility or liability under any statute save where any such liability is incapable of disclaimer.