Working in the Sun and Heat

For those working outdoors, there is the added risk of sun exposure. Exposure to ultraviolet radiation (UV) from the sun can cause skin damage including sunburn, blistering and , in the long term, skin cancer.

UV exposure can occur even on overcast days. Bear in mind that UV radiation is at its peak between 11am and 3pm and efforts should be concentrated at reducing exposure during these times.

Where the environment has a high temperature or humidity, there is an increased risk of heat stress. Heat stress is not only a risk to outdoor workers but also to workers within high temperature workplaces, such as those involving hot industrial processes or where the space is unventilated and naturally accumulates heat, e.g. in attics.


According to the latest available statistics:

  • There are around 16,700 new melanoma skin cancer cases in the UK every year, that’s 46 every day (2016-2018)
  • There were 2,341 deaths from melanoma skin cancer in the UK between 2017-2019
  • Over the last decade, melanoma skin cancer incidence rates have increased by around a third (32%) in the UK. Rates in females have increased by more than a quarter (27%), and rates in males have increased by almost two-fifths (38%) (2016-2018). 86% of melanoma skin cancer4 cases in the UK are preventable.
  • Melanoma skin cancer is the 5th most common cancer in the UK, accounting for 4% of all new cancer cases (2016-2018)
  • Melanoma skin cancer is the 20th most common cause of cancer death in the UK, accounting for 1% of all cancer deaths (2017-2019)


  • The Workplace (Health, Safety and Welfare) Regulations 1992 require that a ‘reasonable temperature’ should be maintained inside buildings used as workplaces
  • The Approved Code of Practice (L24) goes on to provide that, where reasonable comfort cannot be achieved, e.g. because of hot processes, ‘all reasonable steps should be taken to achieve a temperature which is as close as possible to comfortable’
  • The Health and Safety at Work etc Act 1974 – places a duty on every employer to ensure, as far as is reasonably practicable, the health, safety, and welfare at work of all their employees. ‘Health’ includes mental health
  • The Personal Protective Equipment at Work Regulations 1992 (as amended) require that employers select, provide, and maintain suitable PPE for employees and that they should instruct staff in how and when to use it. PPE worn by employees, the Personal Protective Equipment (PPE) at Work Regulations require employers to consider the work environment such as the weather, if the work is outside
  • The Construction (Design and Management) Regulations 2015 also require that indoor construction site temperatures be ‘reasonable’
  • The Management of Health and Safety at Work Regulations 1999 – place a duty on employers to make a suitable and sufficient assessment of the risks to health and safety to which employees are exposed whilst they are at work.

The regulations also require that workplaces should be adequately thermally insulated which, although in most cases is a reference to retention of heat, could be construed in extreme environments as providing insulation from heat. Furthermore, regulations require that the excessive effects of sunlight on temperature must be avoided.

No upper limit of temperature is given, though, based on industry and HSE guidance, anything above 24°C is not regarded as comfortable.


UV exposure can occur even on overcast days. Bear in mind that UV radiation is at its peak between 11am and 3pm and efforts should be concentrated at reducing exposure during these times.

Clothing can be purchased with sun protection factors assigned, although HSE’s general advice is that a fine weave will provide more protection than a loose weave. This should be taken into account when specifying corporate clothing for outdoor workers.

Sunglasses should be provided where needed to protect workers from the hazard of UV radiation. This is especially the case for those working around water or on snow. Ultraviolet light is intensified and potentially more damaging to the eyes and visual system when it is reflected off the surface of water or snow. Sun exposure has been connected with eye diseases including cataracts and macular degeneration, dry eyes, corneal growths and keratitis or sunburn to the cornea. Sunglasses provided for workers should meet BS EN ISO 12312-1:2022.


To protect those working out of doors, employers need to consider, in their risk assessments, protection from the sun and whether workers need protection from heat stress.

Heat stress is not only a risk to outdoor workers but also to workers within high temperature workplaces, such as those involving hot industrial processes or where the space is unventilated and naturally accumulates heat, e.g. in attics. It is also a concern where work is strenuous and involves wearing protective clothing and for outdoor workers in hot environments. Where the environment has a high humidity, there is an increased risk of heat stress.

What is Heat Stress?

Heat stress occurs when the body is forced to work hard to control its core temperature. This can occur when:

  • Sweat evaporation is restricted by the type of clothing and / or the humidity of the environment
  • Heat will be produced within the body due to the work rate and, if insufficient heat is lost, core body temperature will rise
  • Core body temperature rises causes the body to react by increasing the amount of sweat produced, which may lead to dehydration
  • Heart rate also increases which puts additional strain on the body
  • If the body is gaining more heat than it can lose the deep body temperature will continue to rise
  • Eventually it reaches a point when the body’s control mechanism itself starts to fail

As deep body temperature rises, the body reacts by increasing the amount of sweat produced, which may lead to dehydration. The heart rate increases placing additional strain on the body. Eventually it reaches a point when the body’s control mechanism starts to fail. Typical symptoms are:

  • An ability to concentrate
  • Muscle cramps
  • Heat rash
  • Severe thirst – a late symptom of heat stress
  • Fainting
  • Heat exhaustion – fatigue, giddiness, nausea, headache, clammy skin
  • Heat stroke – hot dry skin, confusion, convulsions, and eventual loss of consciousness. This is the most severe disorder and can result in permanent brain damage or death if not detected at an early stage

Treatment of the early symptoms, by removing the individual to a cool environment, it is essential to avoid heat exhaustion or heat stroke.

If managers are worried that an employee is showing signs of excessive stress, they should encourage them to see the GP, or refer them to the organisation’s occupational health service where available.

Risk-assessing Heat Stress

When carrying out a risk assessment, the first aspect of the assessment is to understand the degree of hazard involved. The factors that need to be considered are the:

  • Air temperature – this is the temperature of the air surrounding the body
  • Radiant heat – thermal radiation is the heat that radiates from a warm object and can be present even if there are no heat sources. Radiant temperature has a greater influence over air temperature on how we lose or gain heat from the environment. Examples of radiant heat are sun, fire, ovens, molten metals, and dryer machinery.
  • Air velocity –  the speed at which air moves across the employee to keep them cool, if the air is cooler than the environment. Instances where air velocity is an important factor to thermal comfort include still or stagnant air in an indoor environment that is artificially heated, which can feel stuffy. Also phycisal activity increase air movement, so air velocity may be corrected to account for a person’s level of physical activity.
  • Humidity – when water is heated and evaporates into the surrounding environment, the resulting amount of water in the air will provide humidity. Relative humidity is the actual amount of water vapour in the air and the maximum amount of water vapour that the air can hold at that air temperature. Relative humidity between 40% and 70% does not have a major impact on thermal comfort. In workplaces which are not air conditioned, or where the weather conditions outdoors may influence the indoor thermal environment, relative humidity may be higher than 70%. Humidity in indoor environments can vary greatly and may be dependant on whether there are drying processes (paper mills, laundry etc) where steam is given off. High humidity environments have a lot of vapour in the air, which prevents the evaporation of sweat from the skin. In hot environments, humidity is important because less sweat evaporates when humidity is high (80%+). The evaporation of sweat is the main method of heat reduction. When non-breathable vapour-impermeable personal protective equipment (PPE) is worn, the humidity inside the garment increases as the wearer sweats because the sweat cannot evaporate. If an employee is wearing this type of PPE (e.g. asbestos or chemical protection suits etc) the humidity within the PPE will be high.
  • Levels of physical work – the more physical work a person does, the more heat they will produce. The more heat produced; the more heat needs to be lost so they don’t overheat. The impact of metabolic rate on thermal comfort is critical. A persons physical characteristics should always be borne in mind when considering their thermal comfort, as factors such as their size and weight, age, fitness level and sex can all have an impact on how they feel, even if other factors such as air temperature, humidity and air velocity are all constant.
  • Clothing insulation – the amount and type of clothing being worn (impervious clothing impedes heat loss and is said to cause heat stress at temperatures as low as 21°C if activities are strenuous). Wearing too much clothing or PPE may be a primary cause of heat stress even if the environment is not considered warm or hot. It is important to identify how the clothing contributes to thermal comfort or discomfort. By periodically evaluating the level of protection provided by existing PPE and evaluating newer types of PPE it may be possible to improve the level of thermal comfort. Where PPE is uncomfortable it will also encourage workers to remove them and therefore change the risk of exposure or protection from hazards – which would be a detrimental consequence.


Actions that an employer can introduce to help manage working in the sun and heat include:

  • Scheduling indoor jobs for the middle of the day and outdoor tasks to the start and end, to avoid peak exposures
  • Rotating staff to limit exposure times
  • Providing shelter either for the work or, where not practicable, for breaks
  • Encouraging or requiring staff to cover up and wear sunglasses
  • Providing hats that shade the neck, face and ears
  • Providing SPF 15+ sunscreen
  • Include sun exposure and heat stress within risk assessments as appropriate to the work
  • Consult with workers when undertaking risk assessments and before introducing new ways of working
  • Provide cool drinking water and encourage workers to drink plenty of water regularly to prevent dehydration
  • Increase the number of rest breaks in cool / shaded locations. Av cooled rest area may be required indoors
  • Ensure that contractors are also aware of the risks and are taking preventative actions
  • Give sun protection / heat stress advice to staff and managers
  • Take account of sun and heat stress risks in first aid provisions
  • Consider the risks of heat stress when selecting clothing and PPE
  • Take action to reduce exposure to a safe level, e.g. by the timing of work, managing exposure times, providing shelter
  • Provide training for your workers, especially new and young employees telling them about the risks of heat stress associated with their work, what symptoms to look out for, safe working practices and emergency procedures
  • Defining safe systems of work and training managers and staff in them (in industries with a significant heat stress issue these should ve based on medical assessment and advice)

Actions that an employee can introduce to help manage working in the sun and heat include:

The HSE has produced a sun protection six-point code for workers:

  • Keep your top on so you do not expose unprotected areas; clothing forms a barrier to the suns harmful rays, especially tightly woven fabrics
  • Wear a hat with a brim or flap that covers the back of the neck and ears to avoid sunburn
  • Stay in the shade whenever possible, especially at lunchtime
  • Use a high factor sunscreen of at least factor SPF15 on exposed skin. Apply as directed on the product
  • Drink plenty of water to avoid dehydration
  • Check your skin regularly for unusual spots or moles that may have changed. See a doctor immediately if you see anything that has changed in shape, size, colour, or is itching or bleeding
  • Remember: those with pale skin, freckles, moles, a family history of skin cancer or those who work outdoors have increased risks of skin damage
  • Ensuring they behave responsibly to themselves and others to minimise pressures and demands
  • Reporting concerns to their line manager
  • Request welfare meetings – to have opportunities to express any concerns
  • Considering opportunities for counselling when recommended
  • Ensuring they are meaningfully involved in the stress risk assessment process
  • Seeking advice from Human Resources, Occupational Health, or their GP when needed
  • Being supportive of their colleagues as far as they are able