High temperatures encountered this summer have certainly raised concerns throughout industry regarding the health and safety of employees that conduct manual labour in these conditions.
Heat stress may be defined as the combined effect of the work environment and the physical demands of the job that constitutes a total heat load on the body. From this definition, we can see that there are two sources of heat that must be taken into account in the evaluation of heat stress, namely externally imposed environmental heat and internally generated metabolic heat.
In spite of heat from the environment and the production of metabolic heat in the core of the body, body temperature remains remarkably constant and is regulated between narrow limits around 37 ºC. When an individual is exposed to such an extent that the body is unsuccessful in maintaining its temperature, the person may suffer from heat related diseases.
There are four diseases or conditions associated with exposure to heat. Heat collapse and heat stroke are the two most serious conditions. If a person with heat collapse is not treated immediately and correctly he may suffer from heat stroke.
Heat stroke is a dangerous condition characterised by a body temperature of 41 ºC and higher. The condition is brought on by the total collapse of the body’s defense mechanisms against the high environmental heat load.
In order to determine the extent of heat exposure and the control measures applicable, the amount of heat stress an employee is exposed to, should be determined. The four measurable factors that will determine the level of heat stress imposed by the environment are, air temperature, radiant heat exchange, air movement and humidity.
All four measurable factors are incorporated into one unit, the Wet Bulb Globe Temperature (WBGT) Index. The heat stress experienced by an individual can therefore be expressed as a single number in this way. The WBGT Index takes all the environmental factors into account and should be evaluated against the permissible exposure threshold limit values for workloads. By doing this, the environmental factors, metabolic heat as well as the workload are considered.
The employer is compelled by means of legislation to keep exposure of employees to heat stress within limits. Exposure to heat in the workplace is governed by Regulation 2(4) of the Environmental Regulations for Workplaces, OHSAct (85 of 1993). According to the above regulation, an employer shall introduce control measures where the time weighted average WBGT Index, determined over a period of one hour, exceeds 30 in the environment in which an employee works.
Measures to control employee exposure to heat stress may range from expensive engineering control methods to less costly methods, including personal protective equipment, physiological and administrative controls.
Every situation in industry is different and it is therefore important to know which control measures to implement.
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