Summer brings one of the most overlooked hazards in the UK workplace. Heat stress is not a minor inconvenience — it can injure, and in extreme cases kill, and it exposes employers to real legal and financial liability. Yet many businesses still have no formal plan for managing it. This guide explains what heat stress is, the law behind it, the warning signs, and the training your team needs to stay safe and compliant.
Employer duty of care
The Health and Safety at Work etc. Act 1974 requires every employer to protect workers from foreseeable harm — and that includes thermal hazards. There is no maximum legal working temperature in the UK, but courts and tribunals still expect employers to act when conditions become harmful. Failure to do so can lead to enforcement action and civil claims.
What is heat stress?
Heat stress occurs when the body’s natural cooling can no longer maintain a safe core temperature. Unlike ordinary physical fatigue, it can escalate from mild discomfort to a medical emergency — heatstroke — within hours if the warning signs are ignored.
Those most at risk include workers in construction, agriculture, utilities, logistics and warehousing, and anyone doing heavy physical work or exposed to direct sun. But indoor workers in poorly ventilated factories, kitchens and laundries are just as vulnerable.
Warning signs to know
| Severity | Symptoms |
|---|---|
| Early | Heat rash and prickling skin; excessive sweating and thirst |
| Moderate | Dizziness and fatigue; headache and nausea |
| Serious | Muscle cramps; rapid heartbeat and confusion |
| Emergency | Loss of consciousness; heatstroke — call 999 immediately |
What does UK law require?
There is no maximum legal working temperature in the UK. But several pieces of legislation create clear duties for employers:
The legal framework
- Health and Safety at Work etc. Act 1974 — protect workers from all foreseeable harm, including thermal hazards.
- Workplace (Health, Safety and Welfare) Regulations 1992 — indoor temperatures must be “reasonable” during working hours, with thermometers available.
- Management of Health and Safety at Work Regulations 1999 — formally assess risks and put appropriate controls in place.
- HSE guidance on thermal comfort — not statutory, but courts increasingly reference it when judging whether an employer acted responsibly.
The key point: the absence of a maximum temperature does not reduce your liability. If a worker is harmed and you hadn’t done a heat risk assessment or put controls in place, you’re likely to face enforcement action. The question a court asks is “was the risk foreseeable?” — and in a UK summer, the answer is almost always yes. With UKHSA’s Adverse Weather and Health Plan for England now updated for 2026–27 and heat episodes becoming more frequent, this is only moving up the agenda.
The 6-step approach to managing heat risk
Conduct a thermal risk assessment
Identify who’s exposed, how often and under what conditions. Factor in work rate, clothing, humidity, ventilation and individual vulnerability — pregnant workers, older employees, those with heart or respiratory conditions. Document controls and review when a heatwave is forecast.
Engineering controls first
Eliminate the hazard at source where you can: improve ventilation, add fans or air conditioning, insulate hot surfaces, and schedule heavy work for cooler parts of the day. Engineering controls take priority over administrative measures.
Administrative controls
Rotate jobs, increase rest breaks, move work to cooler areas, and allow flexible start times during heatwaves. Provide shaded rest areas and cool drinking water — around 250ml per hour for those working in hot conditions.
Acclimatise new workers
Those new to hot conditions should build up exposure gradually over 7–14 days. Acclimatisation significantly cuts the risk of heat illness during the first two weeks in a new environment.
Train supervisors to spot symptoms
This is where formal training becomes non-negotiable. First aiders and line managers must be able to identify early-stage heat illness, act quickly and follow your emergency procedures. A confused worker losing consciousness needs an emergency response — not a glass of water and a sit-down.
Monitor and review
Give workers a simple way to report feeling unwell, and never dismiss complaints of dizziness or nausea in hot weather. Review your controls after any incident and ahead of each summer.
Which training covers heat risk?
Heat stress management sits within several accredited qualifications available through Envico:
NEBOSH National General Certificate
Covers thermal comfort, risk assessment and occupational health — the benchmark H&S qualification for the UK workplace.
NEBOSH Construction Certificate
For construction managers — includes heat, UV and outdoor environmental hazards specific to site work.
IOSH Managing Safely
For managers and supervisors who need to identify hazards, assess risk and implement controls — heat risk included. See also all IOSH courses.
Risk Assessment training
Learn to conduct and document workplace risk assessments, including thermal comfort and heat stress controls.
First Aid training
Equip first aiders to recognise and respond to heat exhaustion and heatstroke.
Don’t wait for a heatwave warning
The most common mistake is treating heat as a reactive issue — acting only when a forecast hits 30°C. By then, untrained supervisors, missing risk assessments and inadequate rest provision are already putting people at risk. The time to train your team, update your assessments and put a heat management plan in place is before temperatures peak — not during.
Frequently asked questions
Is there a maximum legal working temperature in the UK?
No. There’s no statutory maximum. But employers still have a duty under the Health and Safety at Work Act 1974 to protect workers from foreseeable harm, and indoor temperatures must be “reasonable” under the 1992 Workplace Regulations. The lack of a fixed limit doesn’t remove your liability.
What should I do if a worker shows signs of heatstroke?
Heatstroke is a medical emergency — call 999 immediately. Signs include confusion and loss of consciousness. Don’t treat it as something a short break and a drink will fix; rapid professional intervention can be life-saving.
Do I legally need a heat risk assessment?
The Management Regulations 1999 require employers to assess foreseeable risks and control them — and in a UK summer, heat is foreseeable. So while no rule names a “heat risk assessment” specifically, assessing and controlling heat risk falls squarely within your existing legal duties.
How much water should workers have in hot conditions?
As a guide, provide cool drinking water at around 250ml per hour for workers in hot conditions, alongside shaded rest areas and adjusted break schedules.