When is it too hot to work?
Risk analysis and technical and organisational measures


Belgium has been experiencing several heatwaves recently. While some people are enjoying it, others are suffering, such as workers in offices without air conditioning or those outside who are exposed to the sun's rays. This is an unusual situation that raises some questions: can workers simply stop working in such weather conditions?

The answer is no. But when the situation becomes too hot at work, workers are entitled to a number of protective measures. Employers are not always aware of their obligations in this regard and generally have not conducted the required risk analysis.

When is it too hot to work?

Heat is typically measured on a thermometer. However, the action value for heat exposure in the workplace is not expressed in Celsius but by using the wet bulb globe temperature (WBGT) index, which also takes into account the air temperature, relative air humidity, air velocity and thermal radiation due to the sun or technological conditions.

Employer in Belgium are familiar with this index, which can be measured using a "wet globe" thermometer or, in its absence, a regular thermometer with a special conversion mechanism included in the Well-Being at Work Code.

Whether it is "too hot" to work will depend on the type and intensity of the work to be performed and the WBGT index:

Physical workload

WBGT index maximum

Light or very light work

(eg, secretarial work, driving a car, manual work at a desk)


Semi-heavy work

(eg, carpentry, driving a tractor)


Heavy work

(eg, digging, hand sawing, pushing and pulling wheelbarrows)


Very heavy work

(eg, deep digging and excavation, climbing ladders and stairs)


It is up to the prevention advisor-occupational physician to classify (in advance) the different functions and tasks into the various job categories:

  • light work;
  • semi-heavy work;
  • heavy work; and
  • very heavy work.

Once the employer has calculated the WBGT index and is aware of the workload per workstation, the employer can then check if the workers are facing a high temperature and whether specific measures should be taken.

Risk analysis and technical and organisational measures

Every employer must carry out a risk analysis of the technological or thermal weather environments present in the workplace. In particular, the employer must consider the following factors:(1)

  • the air temperature;
  • the relative humidity of the air;
  • air speed;
  • the thermal radiation due to the sun or technological conditions;
  • the physical workload;
  • the work methods and work equipment used;
  • the characteristics of the work clothing and PPE; and
  • the combination of all these factors.

The risk analysis must take into account the evolution of these factors over the duration of the work, the frequently changing work circumstances and seasonal variations.

As part of the risk analysis, the employer must evaluate the thermal environments and, if necessary, measure them.(2) The measurement and calculation methods used must be determined after consultation with the prevention advisor-occupational physician or the prevention advisor occupational hygiene (who is part of the external service for prevention and protection at work) and after agreement with the committee for prevention and protection at work (CPPW). If no agreement is reached within the CPPW, then the employer must choose one of the methods whose references are published on the Federal Public Service Employment, Labour and Social Dialogue website.

When WBGT values are likely to exceed the set action values, the employer must, on the basis of the risk analysis, draw up a programme of technical and organisational measures to prevent or minimise heat exposure and the resulting risks. The CPPW must also give its opinion on this programme of measures, which is then included in the overall prevention plan.

When drawing up the programme, the employer must consider different types of measures, such as:

  • technical measures that act on humidity and thermal radiation;
  • adapt work equipment or work methods;
  • limit the duration and intensity of exposure;
  • adapt working hours or the work organisation so that the duration of the worker's exposure to excessive heat is reduced; or
  • provide protective work clothing and free refreshing drinks.

The employer must implement this programme as soon as the action values are exceeded.


In the event of extreme heat resulting from weather conditions (eg, a heatwave) that involve the transgression of the action values, the employer must take the following measures (in accordance with the drafted programme of technical and organisational measures or in the absence of such a programme):

  • ensure the provision of refreshing beverages, free of charge to workers;
  • protect workers against solar radiation – this can be achieved by personal or collective means of protection (eg, sunscreen, hat and sun covers) or by adapting the organisation of work;
  • install an artificial ventilation device within 48 hours of the values exceeding the thresholds; and
  • if the values exceed the thresholds for more than 48 hours, introduce a regime of limited presence in the workplace and also rest periods. The employer can either base these rest periods on certain International Organization for Standardization (ISO) norms(3) or ask the opinion of the prevention advisor-occupational physician and obtain the agreement of the CPPW or, in the latter's absence, of the trade union delegation. In the absence of an agreement, the employer must apply the following rest periods:(4)

Alternation of work

WBGT index value

Light work

Semi-heavy work

Heavy work

Very heavy work

45 minutes of work – 15 minutes of rest





30 minutes of work – 30 minutes of rest





Information for workers
Workers exposed to excessive heat (for weather or technological reasons) must receive information and training about:

  • the results of the risk analysis;
  • the measurement and exposure results;
  • action values;
  • preventive measures;
  • how to detect and report physical symptoms relating to excessive cold or heat;
  • safe behaviour; and
  • health surveillance.

Temporary unemployment scheme?
If it is impossible for workers to start their work due to the announced heat, employers may submit a request for temporary unemployment due to bad weather to the Unemployment Office (ONEM/RVA).

Weather conditions must be such as to make it impossible to perform the work. The introduction of such a regime is not permitted when the heat only hinders the performance of the work or reduces productivity. When it is very hot, for example, if concrete or masonry dries too quickly and the relevant materials cannot be worked with, then it will be admissible to put workers on temporary unemployment.

In these cases, the temperatures must be high and persistent. The ONEM/RVA ultimately decides whether the temperatures are high enough to prevent such work from being carried out.

Temporary unemployment must always cover a full working day. If workers have to interrupt their work after a few hours because of the extreme heat, temporary unemployment will not be possible.

For further information on this topic please contact Astrid Caporali or Myriem Ahdach at ALTIUS by telephone (+32 2 426 1414) or email ([email protected] or [email protected]). The ALTIUS website can be accessed at


(1) Article V.1-1 of the Well-Being at Work Code.

(2) The thermal environments concern work with exposure to heat and work with exposure to cold.

(3) NBN EN ISO 7243, NBN EN ISO 7933 or NBN EN ISO 9886 norm.

(4) Annex V.1-1 of the Well-Being at Work Code.