Too Hot to Handle? Legal Realities of Workplace Heat Stress

Headnote: This Update examines employers’ legal obligations in respect of workplace heat stress in Malaysia, with particular reference to the DOSH Guidelines on Heat Stress Management at Workplace 2016. It sets out the structured HIRARC compliance framework – covering hazard identification, WBGT-based risk assessment, tiered control measures, record-keeping, and training – applicable across all industries, including corporate and service-sector settings with outdoor-facing roles.

Introduction

Malaysia’s tropical climate poses a persistent yet often underestimated occupational hazard. With rising temperatures and increasing reports of work hours lost to extreme heat, employers across all industries – not only in construction and manufacturing, but also in corporate and service-sector settings where workers are periodically required to perform outdoors tasks – must take legally defensible steps to manage heat stress risks. This advisory sets out the Malaysian legal framework governing workplace heat stress and the practical compliance measures that employers should implement to discharge their obligations.

Part I: The Legal Framework in Malaysia

Occupational Safety and Health Act 1994 (Act 514)

The primary legislation governing workplace safety and health including heat stress management in Malaysia is the Occupational Safety and Health Act 1994 (“OSHA“) as amended by the Occupational Safety and Health (Amendment) Act 2022 (“2022 Amendment Act“). Section 15(1) and section 15(2)(e) of the OSHA impose a general duty on employers and self-employed persons to provide and maintain a working environment that is, so far as is practicable, safe and without risk to the health of their employees. This duty is broadly worded and, following the 2022 Amendment Act which came into force on 1 June 2024, applies to all places of work without exception including any place where people are at work.

Factories and Machinery Act 1967 (Act 139) and Subsidiary Legislation

The Factories and Machinery Act 1967 (“FMA“) has been repealed by the 2022 Amendment Act, effective 1 June 2024. However, the subsidiary legislation made under the FMA remains in force and continues to apply until expressly revoked or replaced. In particular, the Factories and Machinery (Safety, Health and Welfare) Regulation 1970 remains valid and continues to empower Inspectors to: (i) require suitable measures to reduce heat effects where operations or processes give rise to undue heat (Regulation 28(1)); (ii) mandate adequate means to cool the air or create air movement (Regulation 28(2)); and (iii) require insulation or heat-reflecting treatment of buildings with high heat transmission coefficients (Regulation 28(3)).

Employers should therefore not assume that the repeal of the FMA has diminished the regulatory obligations relating to workplace temperature and heat management; the subsidiary regulations continue to impose binding obligations.

The DOSH Guidelines on Heat Stress Management at Workplace 2016

The Department of Occupational Safety and Health (“DOSH“) published the Guidelines on Heat Stress Management at Workplace 2016 (“DOSH Guidelines“) to provide practical guidance on recognising, estimating, preventing, and treating heat stress at work. Although these guidelines are not strictly binding legislation, they serve as an authoritative reference that employers are requested to adopt and adapt, and compliance with them is regarded as fulfilling the general duties under the OSHA and subsidiary regulations made under the FMA.

Part II: Industries and Workplaces Affected

Heat stress management is not confined to heavy industry and construction. The DOSH Guidelines expressly identify a broad range of affected sectors, including finance, insurance, real estate and business services (e.g. exterior building cleaning, dry cleaning, and domestic waste collection), transport, storage and communication (e.g. mail delivery, vehicle maintenance, and cable installation), wholesale and retail trades (e.g. warehouse stock transfer), and public services (e.g. field training, and road-traffic control).

Workers exposed to hot and humid outdoor conditions face a heightened risk of heat-related illness, particularly those performing physically demanding tasks, wearing bulky or non-breathable protective equipment, or lacking acclimatisation – including new workers, temporary workers, and those returning after a week or more of absence. Pre-existing health conditions further elevate that risk. Corporate offices should therefore not overlook staff who regularly carry out tasks outdoors as part of their roles, such as facilities maintenance personnel, security officers on patrol, couriers, event management staff, and employees conducting site visits, inspections, or surveys. The risk in these groups is often underestimated precisely because the work does not take place in a traditional industrial setting.

Part III: Practical Compliance Steps – the HIRARC Framework

Employers must carry out a structured Hazard Identification, Risk Assessment, and Risk Control (“HIRARC“) process and maintain proper records of every stage. The following sets out the recommended steps.

Step 1: Hazard Identification

Before any heat stress measurement is carried out, employers should identify the hazard and evaluate the risk using a qualitative screening method. The DOSH Guidelines provide a screening checklist (reproduced at Appendix 5 of the Guidelines) based on six key parameters: (i) air temperature, (ii) radiant temperature, (iii) air velocity, (iv) humidity, (v) clothing, and (vi) metabolic rate (work rate). Each parameter is scored and if three or more parameters score greater than 1, there may be a risk of heat stress. If any single parameter scores a value equal to or greater than 5, the current heat stress indices may not be reliable, and expert advice should be sought.

Employers should identify both environmental factors (e.g. air temperature, radiant heat, air velocity, and relative humidity) and non-environmental factors (e.g. clothing and personal protective equipment (“PPE“), health conditions, acclimatisation, hydration, metabolic heat, and work rate). It is important to note that air temperature alone is not a valid or accurate indicator of heat stress – it must always be considered in relation to other environmental and personal factors.

Step 2: Risk Assessment – Measuring How Hot it Really Feels

Where the screening in Step 1 indicates a potential risk, employers should proceed to a more precise, quantitative assessment. Crucially, this does not mean simply checking the weather forecast or reading an ordinary thermometer. The standard measure used is the Wet Bulb Globe Temperature (“WBGT“) index, which is the most widely used and accepted index for assessing heat stress in industry. In practical terms, the WBGT index combines the effects of air temperature, humidity, wind speed, and radiant heat (such as heat radiating from the sun or hot machinery) into a single reading that reflects how the human body experiences heat – not merely the number on a thermometer.

What employers need to do in practice: Employers are not expected to perform these calculations themselves; they should engage a competent occupational safety and health practitioner or certified assessor to carry out WBGT measurements using specialised equipment. The key practical points are as follows:

1. The WBGT formula differs for indoor and outdoor settings. For indoor work without direct sunlight, WBGT = 0.7 Tnwb + 0.3 Tg; for outdoor work with sun exposure, WBGT = 0.7 Tnwb + 0.2 Tg + 0.1 Tdb. In these formulae, “Tnwb” (natural wet bulb temperature) captures humidity, “Tg” (globe temperature) captures radiant heat, and “Tdb” (dry bulb temperature) is the ordinary air temperature.

2. The resulting WBGT reading must then be adjusted for the type of clothing or protective equipment worn and the physical intensity of the work (known as the metabolic rate). For example, a worker in heavy coveralls or chemical-resistant suits will experience significantly greater heat stress than one in light clothing performing the same task.

3. Measurements should be taken over one hour at the time and location where heat stress is expected to peak typically around midday or during peak operational periods – at five-minute intervals, yielding 12 samples.

In short, the WBGT provides an objective, scientifically grounded measure of how dangerous heat conditions truly is for workers, capturing factors that an ordinary temperature reading would miss entirely.

Step 3: Risk Evaluation – Understanding What the Numbers Mean

The adjusted WBGT reading is assessed against two benchmarks published by the American Conference of Governmental Industrial Hygienists (“ACGIH“): the Action Limit (“AL“) and the Threshold Limit Value (“TLV“). The AL is the more conservative threshold, designed to protect workers who have not yet acclimatised –  that is, workers whose bodies have not had sufficient time to adjust physiologically to working in hot conditions (a process that typically takes seven to 14 days of gradual exposure). The TLV is the upper threshold, applicable to workers who are fully acclimatised. Both benchmarks vary according to work intensity and the prescribed work-to-rest ratio in each hour.

Malaysia does not have its own domestically legislated numerical limits for heat stress. Instead, the DOSH Guidelines adopt the ACGIH’s AL and TLV as the applicable benchmarks. Although these do not carry the formal status of domestically enacted law, compliance with them is regarded as fulfilling the general duty of care under the OSHA, and any departure would require justification with credible evidence. The ACGIH updates its TLVs periodically, and employers should ensure their assessors apply the most current edition.

The WBGT reading is used to classify exposure into three risk categories:

1. Low Risk (WBGT below the AL): Heat conditions are within acceptable limits for most workers. No immediate intervention is required, but employers should continue to monitor conditions, particularly if temperatures are trending upwards.

2. Medium Risk (WBGT between the AL and the TLV): Heat conditions pose a meaningful risk, particularly for workers who are not yet acclimatised, those with pre-existing health conditions, or those performing physically demanding tasks. Employers must implement general control measures, including training, provision of drinking water, health screening, and encouraging workers to self-limit exposure and report symptoms.

3. High Risk (WBGT exceeds the TLV): Heat conditions exceed safe working limits, and employers must implement job-specific controls – engineering measures (e.g. shading, ventilation, and cooling areas), administrative measures (e.g. mandatory work-rest regimes, acclimatisation protocols, active supervision, and buddy systems), and, as a last resort, specialised PPE.

The WBGT assessment and its resulting risk category determine the minimum level of protective action required. An employer who obtains a WBGT reading but fails to implement the corresponding controls will not have discharged its obligations.

Step 4: Risk Control Measures

The DOSH Guidelines prescribe a tiered set of control measures according to the level of risk:

1. General Controls (Medium Risk and above): (i) providing information, instruction and training to all affected workers; (ii) ensuring the regular provision of drinking water; (iii) encouraging workers to limit their exposure to heat; (iv) encouraging workers to report symptoms to management; (v) promoting healthy lifestyles, including a balanced diet and regular exercise; (vi) conducting health screening and surveillance, including pre-placement medical screening; and (vii) monitoring employees with pre-existing medical conditions.

2. Job-Specific Controls – Engineering (High Risk): (i) reducing workers’ activity through the use mechanical aids; (ii) enclosing or insulating hot surfaces; (iii) shielding workers from radiant heat; (iv) providing air conditioning and adequate ventilation; (v) reducing humidity, where applicable; and (vi) providing rapid cooling areas.

3. Job-Specific Controls – Administrative (High Risk): (i) acclimatising workers; (ii) actively supervising workers; (iii) requiring workers to work in pairs or groups; (iv) ensuring that first aid is readily available; (v) establishing emergency procedures; (vi) establishing work-rest regimes to minimise heat exposure; (vii) providing fluids, including oral rehydration salt drinks, and encouraging regular fluid intake; (viii) providing appropriate clothing; (ix) modifying work practices; and (x) conducting regular health screening, where required.

4. PPE (High Risk): Specific PPE, such as cool vests, reflective suits, heat transfer suits, and cool bandanas should be considered only as a last resort, after all other control measures have been evaluated.

Part IV: Record-Keeping Obligations

Proper documentation is essential to demonstrate legal compliance. Employers should maintain records of all steps in the HIRARC process, including:

1. completed hazard-identification screening checklists, recording the date, workplace description, number of exposed workers, working hours, duration of exposure, identified heat sources, and risk scores assigned to each parameter;

2. WBGT measurement data, including equipment used, serial numbers, calibration dates, all measurement parameters (Tnwb, Tdb, Tg, Rh), clothing adjustment factors applied, metabolic rate assessments, work-rest regimes, and the resulting risk decision;

3. records of control measures implemented, including implementation dates and persons responsible;

4. training records (see Part V below); and

5. health screening and surveillance records, including pre-placement medical assessments and records of any ongoing monitoring of blood pressure, pulse rate, body temperature, and skin hydration.

Part V: Training and Active Supervision – the Critical Differentiator

Findings from DOSH enforcement activities and assessments indicate that employers and employees commonly lack awareness of the risks associated with heat exposure. Training programmes – required from medium risk level upwards – should cover, at a minimum: (i) the recognition of environmental and non-environmental heat stress hazards; (ii) the types of heat-related illness, including heat rash, heat cramps, heat exhaustion, heat syncope, and heat stroke, together with their signs, symptoms, and first aid responses; (iii) acclimatisation requirements (as described in Step 3 above); (iv) proper hydration and electrolyte replacement; (v) the correct use of PPE and its effect on heat exchange; and (vi) emergency procedures, including the duty of employees to take reasonable care for their own safety and health and that of others at work.

In high-risk situations, active supervision is essential. Supervisors should monitor workers for symptoms of heat-related illness, enforce work-rest regimes, monitor adequate fluid intake, and require workers to work in pairs or groups.

Part VI: Key Takeaways and Recommended Actions

Employers across all sectors in Malaysia, including those operating corporate offices with outdoor-facing roles, should take the following practical steps to ensure compliance:

1. Conduct and document a HIRARC assessment for heat stress covering all job roles with potential outdoor exposure, using the DOSH screening checklist as the minimum standard. This includes corporate and service-sector roles that are often overlooked, such as facilities maintenance, security, courier services, and site inspections.

2. Where the screening indicates a risk, carry out quantitative WBGT measurements and record all data meticulously, including equipment calibration records, to create a defensible audit trail.

3. Implement tiered control measures proportionate to the assessed risk level, prioritising engineering and administrative controls before resorting to PPE.

4. Establish a comprehensive training programme on heat stress for all potentially exposed workers – not merely operatives on construction sites – and maintain records of attendance, content delivered, and assessments of comprehension.

5. Institute active supervisory protocols, particularly during periods of extreme heat, including monitoring for symptoms, enforcing work-rest regimes, ensuring hydration, and requiring the buddy system for high-risk tasks.

6. Implement acclimatisation procedures for new employees, temporary workers, and those returning from leave of a week or more, assigning approximately half the normal workload on the first day and increasing gradually over seven to 14 days.

7. Establish health screening and surveillance programmes, including pre-placement medical assessments and regular monitoring of chronically exposed workers’ physiological parameters.

8. Review and update all assessments, controls, and training periodically and whenever there is a material change in work processes, environmental conditions, or workforce composition.

Conclusion

Managing heat stress is an obligation that extends well beyond the construction and heavy manufacturing sectors. Under the OSHA (as amended), any employer whose workers are exposed to outdoor conditions, even intermittently, has a legal duty to ensure, so far as is practicable, their safety and health. The DOSH Guidelines provide a clear and structured compliance framework centred on the HIRARC process and supported by measurable assessment criteria.

Notably, Malaysia’s reliance on guidelines, rather than a dedicated statutory standard on heat stress, places a heightened onus on employers to demonstrate proactive compliance through robust documentation and consistent implementation of the HIRARC framework. Proper record-keeping, rigorous training, and active supervisory engagement remain the most critical – yet frequently overlooked – elements of a defensible heat stress management programme.

If you have any queries on the above, please reach out to our team set out on this page. 

For regional employment matters, please see Rajah & Tann Asia’s Employment Practice for more information.

Contribution Note:

This Legal Update is written by Partner Shannon Rajan.