Working in intense heat indoors and outdoors can be harmful

In some workplaces, workers may be exposed to intense heat that can be harmful to health.

In the metal industry, there are, for example, furnaces that generate extreme heat for melting and casting metals and glass, preheating furnaces, heat treatment furnaces, hot rolling mills and drying rooms in paper making. Even within certain food industries there is a risk of exposure to harmful heat.

The employer is responsible for ensuring that the work is planned and performed so that the heat stress is as low as possible and that the maximum permitted value for the time-weighted heat index is not exceeded.

Some work is not covered by the stipulations on work in intense heat

The stipulations on work in intense heat do not apply where solar radiation is the predominant cause of the heat stress, nor to the fire service, since such work must be carried out despite the heat stress.

Also, it is usually not possible to determine the time-weighted heat index for this type of work. The stipulations on working in intense heat are found in the Swedish Work Environment Authority's provisions and general guidelines (AFS 2023:12) on the design of workplaces (so far only in Swedish).

  • The time-weighted heat index is a way of indicating the stress that the body is exposed to through the influence of various climate factors. For example, the higher the humidity, the greater the stress. A humidity of 80 per cent means that 30°C corresponds to a stress of 38°C.

    The time-weighted heat index is also called WBGT, Wet Bulb Globe Temperature. The WBGT method takes into account heat produced by metabolism, heat transferred in various ways to the body from the environment, mainly through thermal radiation and convection, as well as humidity and air velocity.

What are the risks in being exposed to intense heat?

Exposing a person to heat is called heat exposure. Intense heat means heat that can cause a negative heat stress on the body.

Symptoms that can be caused by heat stress:

  • Non-specific discomfort such as irritation, lack of concentration, attention and judgement, reduced performance, increased risk-taking behaviour
  • Heat rash, skin redness and heat rash due to swollen sweat glands.
  • Dizziness and fainting, feeling weak and nauseated when sitting or standing. Short fainting attack, blackout
  • Dehydration through sweating combined with insufficient fluid intake. Headache, thirst, severe fatigue. Feeling of weakness in muscles. Incoherent behaviour.
  • Cramps due to salt loss through excessive sweating
  • Heat stroke – increased pulse rate, confusion. Sweating decreases or stops. Circulatory collapse with unconsciousness and fatal outcome.

Heat stroke is a life-threatening condition. If allowed to continue, it can lead to unconsciousness and death.

Dehydration is caused by cells and organs in the body losing fluid through sweating, while the fluid loss is not compensated for with sufficient water. Dehydration leads to reduced physical work capacity.

High-intensity heat radiation can lead to cataracts. People who have worked with furnaces and smelters for a long time are affected by cataracts to a significantly higher degree than the rest of the population.

  • There are organisational, technical and medical measures that can be taken to reduce and eliminate risks from heat.

    Organisational measures

    • Slow down the pace of work.
    • Increase break time per working hour.
    • Limit total working hours.
    • Introduce short breaks or periods of light activity in a cooler environment.
    • Introduce temporary work rotation to reduce the time employees spend in the hot environment.

    Technical measures

    • At high air temperatures, up to approximately 35°C:
      • Increase air movement by using fans of various types.
    • At high radiant heat:
      • Lower the temperature of the radiation source.
      • Insulate and/or shield the radiation source.
      • Wear heat-insulating or heat-reflecting protective clothing.
    • At high air temperature and high humidity:
      • Use cooled suits.

    Medical measures

    • Non-specific discomfort and heat rash:
      • Avoid heat exposure.
    • In case of dehydration:
      • Drink water and rest in a cool environment.
    • In case of dizziness and fainting:
      • Lie down and drink water.
    • Heat cramps and heat stroke:
      • Rapid cooling and fluid intake.
      • Ambulance transport to hospital.

  • Heat training means a person gradually getting used to heat. The training increases heat tolerance by allowing the body to acclimatise to heat through both physiological and psychological mechanisms.

    The full effect of heat training is only achieved after 8–10 days. But heat tolerance increases after just 3 days. The training is performed so that the employee's working hours in the hot environment are gradually increased through 30, 50 and 80 per cent of the intended working hours.

    In heat-stressed work where there is a risk of exceeding the maximum permissible value for the time-weighted heat index, workers may need a few days of heat training. This applies when a person starts a job that involves heat stress or returns to a job that involves heat stress after, for example, a three-week holiday.

Get a better work environment through working systematically

As an employer, you must manage the work environment systematically, so as to improve it. Our provisions for systematic work environment management apply to all employers – regardless of the activities or the risks that you and your employees could be exposed to.

The employer is responsible for the risks from exposure to intense heat

As an employer, you are responsible for reducing the risk from intense heat, just as you are responsible for all aspects of the work environment. You must be familiar with the Work Environment Act and other work environment regulations.

It is important that the employer informs employees performing heat-stressed work about the risks associated with heat. The information should as a minimum include the health risks that may exist during heat-stressed work, possible and necessary measures in the event of heat stress, preventing dehydration through sufficient fluid intake, the importance of heat tolerance and the importance of heat training.

Employees and safety representatives are important for a good work environment

Employees and safety representatives have an important role in work environment management. As an employer, you must give all employees the opportunity to participate in work environment management. For example, you can let employees suggest measures or provide feedback on measures you have implemented.

Employees' participation in work environment management

As an employee, you must participate in work environment management and participate in implementing the measures needed to achieve a good work environment. You must follow the employer's instructions. You must also report to your employer or your safety representative if the work involves immediate and serious danger to life or health.

Last updated 2025-04-09