In the UK, there is no maximum legal working temperature set in stone. Instead, the law relies on broader principles of safety and welfare. 

• The health, safety and welfare of your workforce: Under the Health and Safety at Work etc. Act 1974, businesses have a legal duty to ensure, so far as is reasonably practicable, the health, safety, and welfare of their workforce.
• Temperature: During working hours, the temperature in all workplaces inside building must be reasonable. Businesses must provide thermometers so the temperature can be measured (The Workplace (Health, Safety and Welfare) Regulations 1992: Regulation 7).

No upper (or lower) legal limit is specified because some workplaces naturally generate high temperatures. There is guidance on the minimum temperature (13 degrees for physical work, or 16 degrees in other situations). The Government is consulting on whether there should be guidance for a maximum temperature as part of the Employment Rights Act reforms.

Instead, the legal focus shifts entirely to risk assessment and mitigation.

• Employees: are covered by all provisions of the Workplace Regulations 1992. They have a statutory right to reasonable indoor working temperatures, adequate ventilation, and access to drinking water. If the heat poses a risk to their health, they are legally protected if they refuse to work under unsafe conditions.
• Workers:  benefit from many of the same core health and safety protections as employees. The screen sector business holds the primary duty of care to ensure the workplace environment does not cause harm to health.
• Freelancers, contractors etc: Strictly speaking, genuinely self-employed freelancers are responsible for their own health and safety on a day-to-day level. However, the screen sector business still controls the premises or location.

A screen sector business must ensure that it does not expose anyone (including freelancers, contractors, and the public) to health and safety risks. If a business fails to manage heat risk and someone collapses from heatstroke, the business could be liable.

For more information on duty of care, please see our other articles: Duty of Care: Employment in the Screen Sector and Duty of Care: Employing Children and Young Persons. 

The HSE explicitly shifts the focus from a "maximum temperature" to the concept of thermal comfort. According to the HSE Thermal Comfort Guidance, thermal comfort describes a person’s psychological and physiological state of satisfaction with their environment.

The HSE highlights six core factors that a business must consider in a hot weather risk assessment:

1. Air temperature: The actual heat of the room or location.
2. Radiant temperature: Heat emitting from equipment (e.g. generators).
3. Air movement: Is there a breeze, or is the air completely stagnant?
4. Humidity: High humidity prevents sweat from evaporating, making it harder for the body to cool down.
5. Clothing: Are cast members in heavy period costumes? Are crew wearing required PPE (like high-vis jackets, hard hats, or safety boots) that traps heat?
6. Work rate: Is the crew doing heavy lifting (e.g., grips, sparks, rigging teams)?

If these factors interact to create a hazard, it can lead to medical emergencies. Everyone can familiarise themselves with the signs of heat stress using the HSE Heat Stress Guide.