Thermal Environment Surveys (Heat & Cold Stress)

Thermal Environment Surveys (Thermal Comfort, Heat & Cold Stress)


MEC work with you to establish the possible causes of workplace ill-health effects by carrying out a thermal environment survey in order to highlight areas of possible concern and recommend, if necessary, controls to improve worker-space health conditions.

What is Heat Stress?

In many jobs heat stress is an issue all year round (such as bakeries, compressed air tunnels, foundries and smelting operations), but thermal comfort levels can be exacerbated during the hot summer months where there may be an increased risk of heat stress for some people.  Heat stress occurs when the body’s means of controlling its internal temperature starts to fail. As well as air temperature, factors such as work rate, humidity and clothing worn while working may lead to heat stress. 

How does the body react to heat?

Someone wearing protective clothing and performing heavy work in hot and humid conditions could be at risk of heat stress because:

  • sweat evaporation is restricted by the type of clothing and the humidity of the environment

  • heat will be produced within the body due to the work rate and, if insufficient heat is lost, core body temperature will rise

  • as core body temperature rises the body reacts by increasing the amount of sweat produced, which may lead to dehydration

  • heart rate also increases which puts additional strain on the body

  • if the body is gaining more heat than it can lose the deep body temperature will continue to rise

  • eventually it reaches a point when the body’s control mechanism itself starts to fail

What are the effects of heat stress?

Heat stress can affect individuals in different ways, and some people are more susceptible to it than others.

Typical symptoms are:

  • an inability to concentrate

  • muscle cramps

  • heat rash

  • severe thirst - a late symptom of heat stress

  • fainting

  • heat exhaustion - fatigue, giddiness, nausea, headache, moist skin

  • heat stroke - hot dry skin, confusion, convulsions and eventual loss of consciousness. This is the most severe disorder and can result in death if not detected at an early stage

Where does heat stress occur?

Examples of workplaces where people might suffer from heat stress because of the hot environment created by the process, or restricted spaces are:

  • glass and rubber manufacturing plants

  • mines

  • compressed air tunnels

  • conventional and nuclear power plants

  • foundries and smelting operations

  • brick-firing and ceramics plants

  • boiler rooms

  • bakeries and catering kitchens

  • laundries

What do I need to do about heat stress?

Where there is a possibility of heat stress occurring you will need to carry out a risk assessment. Controlling the risks in the workplace provides advice on how to carry out a risk assessment.  For specific advice on how to record the findings of your heat stress risk assessment and identifying the heat stress risks you need to control, use the heat stress checklist.

How can I reduce the risks?

  • Remove or reduce the sources of heat where possible

  • Control the temperature

  • Provide mechanical aids where possible to reduce the work rate of employees and regulate the length of exposure

  • Prevent dehydration by providing water-points and regular breaks

  • Provide personal protective equipment (PPE)

  • Provide Training for your workers to make them aware of heat stress symptoms and preventative measures

  • Acclimatisation - ensure workers are 'phased' to hot environments

  • Identify 'at risk workers' and monitor wellbeing - advice may be needed from an occupational health professional or medical practitioner.

Construction Workers at Sunset

What is Cold Stress?


Cold stress is a condition that occurs when the body no longer maintains its normal temperature. Low temperatures, elevated wind speeds, humidity, contact with cold surfaces or water and inadequate clothing are all factors which can cause cold stress.


HSE does not have specific guidance for working in temperatures below 13°C.  You will likely be complying with the law if you work in accordance with British/European Standards but you can demonstrate compliance by alternative means. As a first point of reference you are advised to refer to the British Standards:

When people are too cold?

You can help ensure thermal comfort when working in the cold by:

  • providing adequate workplace heating, eg portable heaters

  • reducing cold exposure by designing processes that minimise exposure to cold areas and cold products where possible

  • reducing draughts

  • providing insulating floor coverings or special footwear when employees have to stand for long periods on cold floors

  • providing appropriate protective clothing for cold environments

  • introducing formal systems of work to limit exposure, eg flexible working patterns, job rotation

  • providing sufficient breaks to enable employees to get hot drinks or to warm up in heated areas

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