heat stress

Heat Stress Assessments

Humans, being Homeotherms (warm-blooded) maintain a core temperature of 37oC+/- 2oC. Movement outside of this range can lead to adverse and potentially fatal effects.  As such the human body is capable of maintaining a heat balance where heat can be gained or lost via various biological actions. However, heat stress can occur when there is a net heat loading on a worker when they are exposed to a hot environment.

The net heat loading is dependent on several factors including the production of heat via metabolic action due to the physical nature of the work, the thermal characteristics that govern heat transfer between the environment and the body via evaporation, convection and radiation and the type of clothing that a worker is wearing while completing their task. It should also be noted that the clothing type may further inhibit the transfer of heat between the body and the environment so care must be taken to ensure suitable clothing is used.

Heat stress occurs when the body’s means of controlling its internal temperature starts to fail. As well as air temperature, factors such as work rate, humidity and clothing worn while working may lead to heat stress. Therefore it may not be obvious to someone passing through the workplace that there is a risk of heat stress. Heat stress can affect individuals in different ways, and some people are more susceptible to it than others.

Typical symptoms are:

  • an inability to concentrate
  • muscle cramps
  • heat rash
  • severe thirst – a late symptom of heat stress
  • fainting
  • heat exhaustion – fatigue, giddiness, nausea, headache, moist skin
  • heat stroke – hot dry skin, confusion, convulsions and eventual loss of consciousness. This is the most severe disorder and can result in death if not detected at an early stage.

The Workplace (Health, Safety and Welfare) Regulations 1992 require during working hours the temperature in all workplaces inside buildings to be ‘reasonable’. Also sufficient numbers of thermometers should be provided to enable workers to determine the workroom temperature. The regulations do not specify maximum or minimum temperatures. The Approved Code of Practice accompanying these regulations advises on measures to achieve compliance including minimum temperatures in work places. The Approved Code of Practice recommends reasonable temperatures in workrooms to be at least 16°C unless much of the work involves severe physical effort, in which case the temperature should be at least 13°C.

The Control of Substances Hazardous to Health (COSHH) Regulations 2002 do not involve the thermal environment directly. However, if thermal conditions influence the extent of a chemical hazard eg by increasing evaporation rates of a toxic substance then they should be included within an assessment under COSHH and have implications on the control measures employed.

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