Workplace Heat Risks

As temperatures continue to climb across the UK, heat is a genuine workplace hazard.

The Health and Safety Executive has been clear: extreme heat should be treated like any other risk capable of causing harm and employers have a legal duty to act.

This post sets out what that duty looks like in practice, who is most at risk and what reasonable controls look like across different types of work.

There Is No Legal Maximum Temperature

One of the most common points of confusion around workplace heat is the absence of a maximum legal working temperature. The UK has no fixed upper limit and that gap in the legislation has led some employers to assume they have no obligation.

That reading is wrong!

The Workplace (Health, Safety and Welfare) Regulations 1992 require employers to provide a reasonable indoor temperature in the workplace.

For areas of construction sites, the Construction (Design and Management) Regulations 2015 require reasonable workplace temperatures. Where the site is outdoors, employers must provide protection from adverse weather and site rest facilities must also be maintained at an appropriate temperature.

For all workers, indoors and outdoors, the Management of Health and Safety at Work Regulations 1999 require employers to assess risks, including thermal risks and put controls in place. Temperature in the workplace is one of the risks that must be assessed, whether the work is being done indoors or outdoors. CDM 2015 also places duties on site operators to provide welfare facilities including drinking water, rest areas, toilets and washing facilities, etc.

The HSE is unambiguous: heat is a hazard. If your workplace, indoors or out, is uncomfortably or dangerously hot, you have a duty to do something about it, regardless of whether a thermometer reading triggers a specific legal threshold.

The TUC and UNISON have both called for a legal maximum working temperature.

Who Is Most at Risk

Heat affects everyone, but some workers face a significantly higher risk of becoming seriously unwell. Risk assessments need to account for these groups specifically.

Outdoor workers: construction workers, agricultural labourers, grounds maintenance staff and delivery drivers are exposed to hot weather, direct sunlight and often physically demanding work. This combination can cause heat stress to develop much more quickly than temperature alone would suggest.

Workers wearing PPE: overalls, respirators, aprons and other protective equipment reduce the body's ability to regulate temperature. Where PPE is required, the risk assessment for the underlying task needs to be reviewed whenever temperatures rise and additional controls should be put in place.

Workers doing physically demanding tasks: manual handling, machine operation and site work all generate body heat. At elevated ambient temperatures, the body's cooling mechanisms come under greater pressure.

Pregnant workers: employers already have a legal duty to carry out risk assessments for pregnant employees. Heat significantly increases the risk of dehydration and heat exhaustion at lower temperatures than for other workers and risk assessments should be reviewed whenever a heat-health alert is issued.

Workers with underlying health conditions: cardiovascular disease, diabetes, respiratory problems and certain medications can all affect how the body responds to heat. Where you are aware of a health condition, individual risk assessment and reasonable adjustments are appropriate.

Older workers: the body's ability to thermoregulate declines with age. The UK Health Security Agency identifies people aged 65 and over as a higher-risk group.

Recognising Heat Exhaustion and Heat Stroke

Understanding the difference between heat exhaustion and heat stroke matters, because one is a medical emergency and the other is not, provided you act quickly enough.

Heat exhaustion develops when the body overheats and begins to struggle to cool itself. Symptoms include heavy sweating, fatigue, headache, dizziness, muscle cramps, nausea and pale, clammy skin. The person may also feel faint or very thirsty. Heat exhaustion does not usually require emergency medical attention if you cool the person down within 30 minutes.

Heat stroke is what happens when heat exhaustion is not treated. The body loses its ability to cool down and core temperature rises to dangerous levels. Symptoms shift: sweating stops, the skin becomes hot and dry and the person may become confused, disorientated or unresponsive. Breathing and heart rate may become rapid. Heat stroke is a medical emergency. Call 999 immediately.

The key practical point for employers is that workers should know the early warning signs and feel comfortable raising the "alarm" early. A culture where workers push through symptoms because they do not want to make a fuss is a culture where heat stroke becomes more likely.

The Legal Duty: What a Risk Assessment Must Cover

A heat-related risk assessment can be completed as part of your existing workplace risk assessments or recorded separately where this makes the risks easier to manage. Employers need to consider how hot weather changes the level of risk and whether existing controls remain suitable.

At a minimum, it should consider:

• The nature of the work and whether it involves significant physical effort;

• Whether workers are indoors or outdoors or a combination;

• Whether PPE is required and how that affects thermal comfort;

• The ventilation and cooling available in the working environment;

• The specific vulnerabilities of your workforce, including any known health conditions and pregnant workers;

• Access to drinking water, rest breaks and shade, etc.

The assessment should then identify the controls you are putting in place, the people responsible for monitoring conditions and what the trigger points are for further action. For example, if a UKHSA Heat-Health Alert is issued for your region.

Practical Controls for Different Working Environments

There is no single solution, because the risks look different depending on where and how people work. The following covers the most common scenarios.

Office and Indoor Environments

Offices can become significantly hotter than ambient outdoor temperatures, particularly in buildings with large windows, limited air conditioning or poor ventilation.

Practical measures include:

• Keeping blinds or curtains closed on sun-facing windows during the hottest part of the day.

• Using fans to improve air circulation, though note that fans become less effective and may worsen dehydration if room temperature exceeds 35°C.

• Relocating workstations away from direct sunlight or heat sources.

• Relaxing dress codes so workers can wear suitable clothing, within any applicable PPE requirements.

• Allowing flexible working hours to avoid commuting or working during the hottest part of the day.

Construction and Outdoor Sites

Outdoor workers are often directly exposed to hot weather, strong sunlight and physically demanding tasks. These conditions can increase the risk of heat stress, so controls need to be planned carefully and adjusted as temperatures rise.

Sensible measures include:

• Scheduling the heaviest physical tasks for early morning or late afternoon, avoiding the 11am–3pm window where possible.

• Providing shaded rest areas on site.

• Making fresh, cool drinking water freely available and reminding workers to drink regularly throughout the shift.

• Providing sun cream with a minimum SPF 30 at no cost to workers.

• Adjusting shift patterns during amber or red heat-health alerts.

• Reviewing PPE requirements and considering whether lighter alternatives are available without compromising protection.

Manufacturing and Industrial Environments

Factory and production environments can reach dangerous temperatures even without exceptional weather, because machinery and process heat add to ambient conditions.

Key controls include:

• Local exhaust ventilation or radiant heat shielding near heat-generating equipment.

• Rotating workers through hot tasks to limit cumulative exposure.

• Providing additional rest breaks in cooler areas.

• Reviewing PPE requirements for tasks in hot zones, where full PPE is required, rotation and shorter work periods become especially important.

• Installing cooling equipment where feasible, including portable air conditioning units in break areas.

Workers Using PPE in Hot Conditions

Where workers must wear significant PPE, respirators, full overalls, sealed suits, the risk of heat stress is substantially higher. The controls need to reflect that.

Employers should:

• Limit the duration of tasks requiring full PPE during hot weather.

• Rotate staff out more frequently and provide adequate recovery time in a cooler environment.

• Brief workers on the signs of heat stress and operate a buddy system so workers are actively monitoring each other.

• Make sure first-aiders are aware of heat-related symptoms and know the protocol.

  
  

The Heat-Health Alert System

The UK Health Security Agency, working with the Met Office, operates a Heat-Health Alert (HHA) system from 1 June to 15 September each year. Alerts are issued by region and run on a colour-coded scale.

Green — no alert. Normal summer planning applies.

Yellow — conditions that may affect vulnerable people. Employers should review risk assessments and confirm controls are in place.

Amber — impacts expected across health services and the wider population. Employers should increase monitoring, review lone working arrangements, check on vulnerable workers and consider scheduling changes.

Red — significant risk to life, including for healthy people. Only critical work should continue. Non-essential outdoor work should stop during the 11am–3pm window.

Employers in the region should monitor alerts during the summer months and have a clear internal process for communicating any escalation to managers and workers.

What Good Looks Like

A few straightforward things separate employers who genuinely manage heat risk.

Water is always available, without workers having to ask. This sounds basic. In practice, on busy sites and in production environments, it is frequently not the case.

Workers know the symptoms. A toolbox talk at the start of the summer season or a brief at the start of a hot week, takes minutes. It means workers can spot early signs in themselves and their colleagues before the situation escalates.

There is a clear escalation process. Workers know what to do if someone becomes unwell. First-aiders know that heat-related illness is a possibility. Managers know to act, not to dismiss complaints as weakness.

Risk assessments are reviewed. When a heat-health alert is issued or when a heatwave is forecast, the existing risk assessment is revisited and updated if the controls are not adequate for the conditions.

Vulnerable workers are identified and supported. Pregnant workers, those with health conditions, older workers and those in heavy PPE are not expected to manage the same exposure as other workers without additional support.

A Note on Remote and Lone Workers

Employers' responsibilities extend beyond the fixed workplace. Remote workers, including those working from home, should have access to guidance on keeping their working environment cool. Lone workers in hot conditions face additional risk because there is no one to spot the early signs of heat stress. Check-in procedures and buddy systems should be reviewed during periods of extreme heat.

Summary

Heat is a workplace hazard. The absence of a legal maximum temperature does not reduce an employer's duty to manage it. A suitable and sufficient risk assessment, proportionate controls and a workforce that knows what to look out for are the foundations of managing heat risk competently.

If you are unsure whether your current risk assessments adequately address heat or if you need support reviewing controls for a specific working environment, we are happy to help.

DuoDynamic Safety Solutions provides health and safety consultancy to businesses across the UK. Get in touch for a free initial consultation.