Heat Stress Assessment in Malaysia: Protecting Workers in a Hot and Humid Climate

Malaysia’s tropical climate makes heat stress one of the most significant workplace health and safety concerns. Whether in construction, manufacturing, plantations, or kitchens, workers are exposed to high temperatures and humidity that can lead to fatigue, heat-related illnesses, and reduced productivity.
A proper heat stress assessment ensures that environmental and job factors are controlled to protect worker health and maintain performance.

Why Heat Stress Assessment is Important

  1. Health and Well-being

Excessive heat exposure can cause dehydration, heat cramps, exhaustion, or even heat stroke — a life-threatening condition. Continuous exposure without proper controls can also affect long-term health and lead to chronic fatigue or reduced tolerance to heat.

  1. Safety Concerns

High body temperature and fatigue reduce alertness and coordination, increasing the likelihood of accidents, especially in heavy industries or outdoor work. Workers may make errors, mishandle tools, or experience dizziness, leading to injuries.

  1. Productivity and Performance

Heat stress reduces focus, work speed, and overall efficiency. Studies show that productivity can decline sharply as the workplace temperature rises beyond comfort levels.

  1. Legal and Regulatory Compliance

Under the Occupational Safety and Health Act (OSHA) 1994, employers in Malaysia are responsible for ensuring safe working conditions.


The Department of Occupational Safety and Health (DOSH) published the Guidelines on Heat Stress Management at Workplace (2016, updated 2019) — the primary reference for assessing and controlling heat stress using internationally recognized methods such as the Wet-Bulb Globe Temperature (WBGT) index.

Key Elements of a Heat Stress Assessment

  1. Environmental Measurement (WBGT)

The WBGT index considers air temperature, humidity, radiant heat, and air movement. Using a WBGT meter, readings should be taken at worker height during peak working hours.
If WBGT exceeds recommended limits, control measures must be implemented immediately.

  1. Workload and Metabolic Rate

Different tasks generate different levels of body heat. DOSH categorizes work as:

  • Light: office or inspection tasks
  • Moderate: machine operation, assembly
  • Heavy: construction, manual handling, foundry work

The heavier the work, the lower the acceptable WBGT limit.

  1. Clothing and Personal Protective Equipment (PPE)

Protective clothing, such as coveralls or chemical suits, reduces the body’s ability to cool down. Clothing correction factors are applied to adjust the WBGT reading to a realistic exposure level.

  1. Work-Rest Cycles

Based on WBGT readings and workload, workers may need structured rest breaks in shaded or air-conditioned areas. DOSH recommends following ACGIH Threshold Limit Values (TLVs) and ISO 7243 standards for safe exposure durations.

  1. Worker Monitoring and Acclimatisation

New or unacclimatised workers are more prone to heat illness. Employers should implement gradual exposure schedules, hydration programs, and health monitoring to prevent incidents.

Benefits of Conducting Heat Stress Assessments

      • Prevents heat-related illnesses and fatalities
      • Improves worker comfort and morale
      • Maintains productivity and performance
      • Ensures compliance with DOSH and legal requirements
      • Builds a proactive safety culture in high-heat industries

Educating Employers and Employees

Employers Can:

      • Conduct regular heat stress assessments following DOSH guidelines
      • Provide shaded rest areas, ventilation, and drinking water stations
      • Implement work-rest cycles and job rotation
      • Train supervisors to recognize symptoms of heat illness

Employees Can:

      • Drink water frequently, even before feeling thirsty
      • Report symptoms such as dizziness or muscle cramps immediately
      • Use lightweight, breathable clothing where possible
      • Follow rest and hydration schedules provided by the employer

Final Thoughts

Heat stress assessment in Malaysia is not just a regulatory exercise — it is a vital part of workplace health and safety. By measuring heat exposure, managing workloads, and promoting hydration and rest, organizations can protect their workers and sustain productivity in Malaysia’s demanding climate.

A safe and healthy workforce thrives best when employers treat heat stress management as both a compliance requirement and a moral responsibility.