Individual personal preference makes it difficult to specify a thermal environment which satisfies everyone. For workplaces where the activity is mainly sedentary, for example offices, the temperature should normally be at least 16 °C. If work involves physical effort, it should be at least 13 °C (unless other laws require lower temperatures).

The risk to the health of those working in hot or cold environments increases as conditions move further away from those generally accepted as comfortable. Risk of heat stress arises, for example, from working in high air temperatures, exposure to high thermal radiation or high levels of humidity, such as those found in foundries, glass works and laundries. Cold stress may arise, for example, from working in cold stores, food preparation areas and in the open air during winter.

Assessment of the risk to workers’ health from working in either a hot or cold environment needs to consider both personal and environmental factors.

Personal factors include:

• Body activity.
• The amount and type of clothing.
• Duration of exposure.

Environmental factors include:

• Ambient temperature and radiant heat.
• Sunlight, wind velocity and the presence of rain or snow if the work is outside.