How is heat stress measured, and when is a survey required?

Short answer: heat stress is measured with the wet-bulb globe temperature (WBGT) index, following SANS 7243, and a survey is required wherever your risk assessment shows that employees may be exposed at or above the 30 °C WBGT limit. The Physical Agents Regulations, 2024 also set an action level of 27 °C WBGT. Monitoring must be done by a competent person, at the frequency your risk assessment sets or at least every 24 months.

Heat stress falls under regulation 10 and Tables 1 and 9 of the Physical Agents Regulations, 2024 (Government Notice 5952, Government Gazette 52226, 6 March 2025), which took effect on publication. They replace the Environmental Regulations for Workplaces, 1987, which regulation 21 repealed 18 months after promulgation, on 6 September 2026. The February 2026 amendment did not change the heat stress provisions.

The two numbers that matter

• Action level, 27 °C WBGT: at or above it, you must identify why the action level was reached and review your control measures to prevent the limit from being reached (regulation 10(2)).

• Occupational exposure limit, 30 °C WBGT: at or above it, the minimum measures in regulation 10(3) apply, as set out below.

Table 1 gives a duration of 1 hour for both, and the limit is a time-weighted average. The regulations define heat stress as the total heat load from metabolic heat, environmental factors and clothing. The work rate and what people wear therefore matter, not only the air temperature.

How heat stress is measured

Regulation 10 requires the heat stress monitoring programme to be conducted in accordance with SANS 7243. Regulation 7 adds the general rules:

• Who: a competent person with the knowledge, training, experience and qualifications relevant to heat stress, familiar with the Occupational Health and Safety Act and its regulations. No approved inspection authority is required.

• Where and when: the measurements must be representative of employees' exposure. Because the limit applies over 1 hour, plan them for the hottest periods of the shift and of the year.

• Instruments: calibrated to a national or international traceable standard.

• Result: exposure levels are quantified and compared with the action level and limit, and you must draw up a documented action plan for the report's recommendations.

Table 9 lists clothing adjustment values (CAV), each a single number added to the WBGT to represent the effect of the clothing worn. Examples:

• Work clothes of woven fabric: 0, the reference ensemble.

• Double-layer woven clothing (generally coveralls over work clothes): 3.

• Vapour-barrier coveralls with a hood, as a single layer: 11.

• A hood of any fabric, with any clothing ensemble: +1.

A survey that ignores clothing can therefore understate the risk.

When a survey is required, and how often

• Risk assessment first: regulation 6 requires a documented risk assessment by a competent person before exposure, as far as reasonably practicable, then at intervals not exceeding 24 months. Its hazard identification must be complete, so it should consider heat wherever people work near furnaces, ovens or other hot processes, in poorly ventilated buildings or outdoors.

• Monitoring: required where that risk assessment shows that any employee may be exposed at or above the 30 °C limit. Repeat it at the frequency the risk assessment sets, or at least every 24 months. An inspector may direct you in writing to repeat it sooner.

• Earlier review: the risk assessment must be reviewed when, for example, work methods, the type of work, plant or protective equipment change, after an incident, or when medical surveillance links an adverse health effect to a physical agent.

What you must do above the limit

Regulation 10(1) requires heat stress to be eliminated at source where reasonably practicable. Where it is not, and exposure is at or above 30 °C WBGT, you must as a minimum:

• use alternative working methods, and install plant and machinery designed to reduce heat stress, where applicable;

• maintain plant, machinery and workplace systems, and review the design and layout of workplaces, workstations and rest facilities;

• review the risk assessment, the monitoring programme, medical screening, medical surveillance and control measures;

• limit the duration and magnitude of exposure;

• put exposed employees through a heat acclimatisation programme;

• provide prompt first aid specific to the adverse health effects of heat stress;

• provide sufficient potable water at the place of work, as determined by the risk assessment;

• provide protective clothing and equipment that takes the CAV in Table 9 into account.

A quick self-check

• Check that your physical agent risk assessment covers heat and is less than 24 months old.

• List the hot processes, hot buildings and outdoor tasks on site, and when they are at their worst.

• Note the protective clothing worn in those areas. Double layers, vapour-barrier suits and hoods raise the CAV.

• Confirm that drinking water is available at the place of work, not only in the canteen.

• Check that employees exposed at or above the limit have been through a heat acclimatisation programme, and that first aiders know how to treat heat illness.

How Qualitas can help

Our heat stress surveys measure thermal conditions at the work positions, take account of workload and clothing, and compare exposure with the 27 °C action level and 30 °C limit. The report, written for management, SHEQ teams and auditors, recommends practical controls, including work-rest regimes where they are needed.

For the wider framework, see our overview of the Physical Agents Regulations, 2024; for cold rooms and freezers, see our article on cold stress rules.

Not sure what your site needs? Start with our free Compliance Gap Analysis, request a quote, or call or WhatsApp 082 649 6599.

This article summarises the Physical Agents Regulations, 2024 (Government Notice 5952, Government Gazette 52226, 6 March 2025), as amended by Government Notice 7149 (Government Gazette 54177, 20 February 2026), for general guidance. It is not legal advice; refer to the regulations and SANS 7243 for the full requirements.

Christo de Wet is a SAIOH-registered occupational hygienist with 15 years' experience and the founder of Qualitas Occupational Consulting.