Measuring heat stress

The guidance is aimed primarily at employers, managers, occupational health professionals and safety personnel. The objective is to provide a systematic, approach to the decisions required to minimise or reduce the risk of heat stress in your workforce. Employees will also find the information useful in understanding why their employer is taking this approach.

There will be workplaces for which the methods described in this guidance may not be able to provide a specific solution and you may be required to seek expert advice. By applying the information in these web pages, you have shown that you have adhered to best practice.

Measuring heat stress

• Wet Bulb Globe temperature index
• Estimating Metabolic Rate
• Physiological Monitoring
• Heart rate
• Estimating Clothing Insulation Values

There are three types of method used for the assessment of hot environments:

• Empirical – Uses laboratory data to predict the likely effects an environment will have on a human, (ie physiological responses); enabling predictions to be made that estimate work rate, metabolic rate, clothing factors etc.
• Direct - Standardised instruments measure environmental parameters eg globe temperature
• Rational - Calculations of the heat exchanges between the employee and the work environment provides a method for predicting employees responses.

The purpose of these methods is to estimate or establish the physiological responses of an individual to their environment.  The end result is to provide a value which allows a comparison between environments, different working situations and different types of clothing to be made.

Obtaining thermal stress indices requires four processes to occur:

• Input Values - enabling calculations to be made from direct measurement or by extrapolation.
• Calculations
• Output Values: - the results from the calculations.
• Interpretations: - of the outputs either by using a heat stress index, the user or both

Why worry about heat stress

Unless someone collapses from heat exhaustion, the possible health effects of working in the heat may not be obvious. This means it requires employers to identify whether those employees who may be at risk from heat stress are suffering from any heat related illnesses. In some situations this may have to be treated with sensitivity eg sustained heat exposure may result in symptom reporting not readily associated with heat exposure eg rashes, impaired male fertility etc. Part of the way of identifying individuals at risk is to use information you will already have to hand for example:

• Look for patterns in absenteeism, types of illnesses and their frequency of occurrence, the nature of employee complaints, etc. Take particular note of where employees work, their job, how experienced they are, whether any illnesses are recurring etc.
• Read through any RIDDOR reports and any internal accident or injury reports. Are there any patterns to the nature of reportable accidents or injuries? Could any repeated accidents be attributed to the effects of heat e.g. fatigue, loss of concentration, etc.;
• Speak to employees, their safety representatives (e.g. unions), to managers in other companies that are involved in the same business as your organisation, contact industry federations or associations etc.

As an aid the flow diagram provides one example of how you would act if heat stress was a problem and what to do at the various risk assessment stages.

Talking about heat stress

When explaining to your employees about what heat stress is remember that this is a two way street and it is important to listen to what all your employees tell you about heat stress. This is important as it helps engage everyone in dealing with heat stress risks. For example, those involved with purchasing personal protective equipment need to be aware that while it can protect against one risk it can contribute to the causes of heat stress.

After you have identified the problems and put forward solutions then as an employer, you need to ensure that individuals carrying out any measurements or implementing methods of managing the risk are trained and fully competent.

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