Last reviewed 11 July 2022

Mike Everley outlines the main risks to be considered when assessing outside work in hot weather and provides guidance on managing these risks.

The weather, when working outdoors, can have a serious impact on an employee's health if the risks have not been properly managed. This impact may be immediate but may occur over a long time period.

The Health and Safety at Work, etc Act 1974 requires employers to provide their employees with, among other things, a safe and healthy working environment. The Management of Health and Safety at Work Regulations 1999 require employers to assess the risks to the health and safety of their employees arising out of their work activity.

Main risks and their control

General hazards

At high temperatures (25°C and above) employees may become drowsy and less aware of dangers. There is also an increased risk of accidents due to slips, trips, falls, poor manual handling, injury from hand tools, etc. Thermal discomfort gives rise to reduced efficiency that can lead to poor decision-making with resultant errors. In addition, exposure to insects and animal faeces, etc, may prove more harmful if the skin is uncovered or the pores are open due to sweating.

Skin cancer and other effects of sunlight

Too much sunlight is harmful to the skin, with a tan indicating that it has become damaged. Particularly vulnerable are those people with:

  • fair or freckled skin that does not tan, or goes red or burns before it tans

  • red or fair hair and light coloured eyes

  • a large number of moles.

Although workers of Asian or Afro-Caribbean origin are at less risk, they should still take care in the sun to avoid eye damage, skin ageing and dehydration.

In the short term, sunburn can blister the skin and make it peel. Over the longer term, it can speed up the ageing of the skin, making it leathery, mottled and wrinkled, with the most serious effect being an increased risk of developing skin cancer.

According to the HSE publication Sun Protection: Advice for Employers of Outdoor Workers, skin cancer is the most common form of cancer in the UK, with over 40,000 new cases diagnosed each year. Therefore, employers should:

  • include sun protection advice in routine health and safety training

  • encourage workers to keep covered up during the summer months (using a long-sleeved shirt and a hat with a brim or flap that protects the ears and neck), especially at lunchtime when the sun is at its hottest

  • encourage workers to use sunscreen of at least Sun Protection Factor 30 on any part of the body they cannot cover up and to apply it as directed on the product

  • encourage workers to take their breaks in the shade, rather than in the sun

  • schedule work to minimise exposure

  • site water points and rest areas in the shade

  • encourage workers to drink plenty of water to avoid dehydration

  • keep workers informed about the dangers of sun exposure

  • encourage workers to check their skin regularly for unusual spots or moles that change size, shape or colour and to seek medical advice promptly if they find anything that causes them concern.

Further information is contained in the HSE publication INDG147 Keep Your Top On: Health Risks from Working in the Sun. This suggests that certain medicines, contact with certain chemicals used at work (eg dyes, wood preservatives, coal-tar and pitch products) and contact with certain plants can all make the skin more sensitive to sunlight.

The first warning sign of skin cancer is often a small scabby spot that does not clear after a few weeks. Also, changed or newly formed moles or any skin discolouration may provide a warning. Particular attention should be paid to any growths that appear on the face, especially around the nose and eyes, or on the backs of the hands. More information on skin types, identifying skin problems and sun protection is available on Cancer Research UK’s website.

Heat stroke and heat stress

Heat stroke occurs when the core body temperature approaches 41°C. It affects the co-ordination of the nervous system and thermal regulation mechanism. Heat stroke carries a high risk of fatality from cardiac or respiratory arrest, can lead to liver failure and must be treated as a medical emergency. Body temperature may rise to 41°C or higher within 10–15 minutes. Warning signs of heat stroke may include:

  • an extremely high body temperature (above 39.5°C, orally)

  • red, hot and dry skin (no sweating)

  • rapid, strong pulse

  • throbbing headache

  • dizziness

  • nausea

  • confusion

  • unconsciousness.

It is important not to give the victim any fluids to drink. While waiting for medical assistance, it may be necessary to:

  • get the victim to a shady area

  • cool the victim rapidly using whatever methods are available, eg immerse the victim in a tub of cool water, place the person in a cool shower, spray the victim with cool water from a hose, sponge the person with cool water, or, if the humidity is low, wrap the victim in a cool, wet sheet and fan them vigorously

  • monitor body temperature and continue cooling efforts until the body temperature drops to 38–39°F.

Where the muscles begin to twitch uncontrollably, it is important to keep the victim from injuring themselves. However, no object should be placed in the mouth. If there is vomiting, it is vital to keep the airway open by turning the victim onto their side.

The HSE information sheet INDG451 Heat Stress in the Workplace states that “as well as air temperature, factors such as work rate, humidity and clothing worn while working may lead to heat stress”. Heavy work in hot and humid conditions can lead to an increased risk of heat stress because:

  • sweat evaporation is restricted by the type of clothing worn and by the humidity of the environment

  • heat will be produced within the body due to the work rate and, if insufficient heat is lost, deep body temperature will rise

  • as deep body temperature rises, the body reacts 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 reaching a point when the body’s control mechanism itself starts to fail

  • the symptoms will worsen the longer the person remains working in the same conditions.

Typical symptoms include:

  • an inability to concentrate

  • muscle cramps

  • heat rash

  • severe thirst — a late symptom of heat stress

  • fainting

  • heat exhaustion — fatigue, giddiness, nausea, headache, moist skin

  • heat stroke — hot dry skin, confusion, convulsions and eventual loss of consciousness.

Heat stroke is the most severe disorder. Remember, it can result in death if not detected at an early stage.

Heat exhaustion

Heat exhaustion results from high body temperature caused by a reduction of blood flow and could drive up core body temperature to 39°C. The reduction of blood flow may result from dehydration under hot conditions or extremely fast heartbeat caused by high temperature and intense physical labour.

Heat exhaustion is a milder form of heat-related illness that can develop after several days of exposure to high temperatures and inadequate or unbalanced replacement of fluids. It is the body's response to an excessive loss of the water and salt contained in sweat. Warning signs of heat exhaustion include: heavy sweating, paleness, muscle cramps, tiredness, weakness, dizziness, headache, nausea or vomiting, fainting and the lowering of mental alertness. The skin may become cool and moist, the pulse rate fast and weak, and breathing fast and shallow. If heat exhaustion is left untreated, it may progress to heat stroke. Cooling measures include:

  • cool, non-alcoholic beverages

  • rest

  • cool shower, bath or sponge bath

  • an air-conditioned environment

  • lightweight clothing.

Heat cramps

Heat cramps can occur when excessive sweating takes place during strenuous activity. The sweating depletes the body's salt and moisture, and the low salt level in the muscles may be the cause of the cramps. Heat cramps can also be a symptom of heat exhaustion. Where they occur, the employee should:

  • stop all activity and sit quietly in a cool place

  • drink clear juice or a sports beverage

  • not return to strenuous activity for a few hours after the cramps subside, because further exertion may lead to heat exhaustion or heat stroke

  • seek medical attention if the heat cramps do not subside within one hour.


Sunburn damages the skin, and although the discomfort is usually minor, with healing usually taking place within a week, more severe sunburn may require medical attention. Symptoms include: the skin becoming red, painful and abnormally warm after sun exposure. However, severe sunburn can cause:

  • fever

  • fluid-filled blisters

  • severe pain.

When treating sunburn:

  • apply cold compresses or immerse the sunburned area in cool water

  • apply moisturising lotion to affected areas (do not use salve, butter or ointment)

  • do not break blisters.

Heat rash

Heat rash is a skin irritation caused by excessive sweating during hot, humid weather. Heat rash looks like a red cluster of pimples or small blisters. It is more likely to occur on the neck and upper chest, in the groin, under the breasts and in elbow creases. The best treatment for heat rash is to provide a cooler, less humid environment. Keep the affected area dry. Dusting powder may be used to increase comfort.

Heat syncope (fainting)

Heat syncope occurs when blood pools in the lower parts of the body, causing a temporary reduction in blood supply to the brain and hence a transient loss of consciousness.

First aid

Although slightly different treatments will be required for different conditions, in general the following is suggested.

  • Move the patient to a cooler place.

  • Lower their body temperature by:

    • removing some of their clothing (only if necessary)

    • wiping their body with a towel soaked in cold water

    • fanning them.

  • If the patient is unconscious, place them in the recovery position.

  • Do not give the patient any food or drink.

  • Send the patient to hospital as soon as possible.

Risk assessment

The main factors to consider when carrying out a risk assessment of outside work in hot weather are: temperature, humidity, heat radiation from direct sunlight, air movement, workload, work clothing and personal protective clothing to be worn, acclimatisation, duration of the work, age or vulnerability of those involved, and any plant or equipment involved that might generate additional heat.

The controls introduced following the risk assessment should adopt the usual hierarchy of control approach. For example:

  • elimination of risks, eg rescheduling the work to cooler periods of the day or using mechanical aids to replace manual work

  • reduction of risks, eg using equipment that generates less heat, doing the work in a way that requires less strenous effort

  • administrative controls and safe work practices, eg the provision of appropriate training and work instructions, additional breaks in cooler areas, cool water and job rotation

  • personal protective equipment, eg the provision of light clothing.

Other steps that can be taken include:

  • introducing shading in areas where individuals are working

  • encouraging the removal of personal protective equipment when resting to help encourage heat loss

  • educating workers to recognise the early symptoms of heat stress.

Finally, the findings of the risk assessment process and the risk control measures introduced should be subject to robust monitoring and review. The review should consider whether changes to policies and practice are required as a result of any:

  • incidents that have occurred

  • evidence that suggests that the risk assessment is no longer valid

  • significant changes that have taken place.

Further information

The following are available from the HSE: