When is it too hot to work?

It is a question that pops up every summer and has started to appear in the recent UK heatwaves: when is it too hot to work? As these summer heatwaves increase, employers need to consider the effect of the heat on employees and what the necessary steps are to protect their health and welfare.

Hot conditions, apart from medical emergencies caused by heat exhaustion or heatstroke, can cause the following concerns:

• loss of concentration;
• increased tiredness;
• dizziness;
• fainting; or
• heat cramps.

The likelihood of accidents may also increase due to reduced concentration and sweating.

Indoor temperatures

Indoor environmental conditions substantially influence health and safety productivity, and the air temperature in the office has a strong effect on working performance.

Although there is some disagreement on the best temperature for productivity, most studies found it is between 21°C and 23°C. It is generally agreed that productivity decreases when office temperatures rise above this:

• an over-hot workplace can impact the health and wellbeing of employees, with risks including dehydration and heat exhaustion or heatstroke;
• if a person's blood temperature rises above 39°C, there is a risk of heatstroke or collapse;
• above 41°C, delirium or confusion can occur, and there is a risk that if blood temperature reaches this level, it can prove fatal or cause irreparable organ damage.

Everyone is different, young people, pregnant women, disabled people and those on certain medication tend to have a lower tolerance to high temperatures, and there is some evidence of a gradual reduction in the effectiveness of the body to regulate its temperature after the age of 60.

In the UK, there is no maximum temperature for workplaces inside buildings, but the Workplace (Health, Safety and Welfare) Regulations SI 1992/3004 require that the temperature in all workplaces inside buildings during working hours is "reasonable".

There is no consensus over what a reasonable temperature is. It depends on the:

• type of work being done - manual, office, etc;
• type of workplace - kitchen, air-conditioned office, etc; and
• nature of the work.

The Health and Safety Executive (HSE) claims that a meaningful maximum temperature cannot be given due to the high temperatures found in, for example, glassworks or foundries. The HSE states that in such environments it is still possible to work safely provided appropriate controls are present. In addition, factors other than air temperature, such as radiant temperature, humidity and air velocity, become more significant and the interaction between them becomes more complex with rising temperatures.

Other factors likely to have an effect, other than the temperature alone, including:

• humidity;
• wind speed;
• radiant heat sources;
• clothing, including personal protective equipment (PPE).

Risk assessment for hot weather

A risk assessment needs to be carried out to assess whether there is a risk of exposure of indoor workers to high temperatures during the summer. This should:

• identify any hazards and problems;
• identify those at risk; and
• indicate the precautions that need to be taken to ensure the health of the workers.

Factors that should be considered during the risk assessment include:

• the climate - air temperature, humidity, air movement, and any heat sources;
• physical activity - how strenuous the physical activity is going to be, the amount of work and time it needs to be done, working hours and the time of day;
• clothing and PPE - how will these contribute to overheating;
• vulnerable workers - young, old, disabled, pregnant employees, or those on medication, and any additional procedures or resources required.

What can employers do?

Employers are not legally obliged to provide air conditioning in workplaces, but are expected to provide reasonable temperatures and a sufficient quantity of fresh or purified air:

• ventilation should be used to combat high temperatures and humidity;
• blinds or curtains can be used to block out sunlight;
• solar control window film can be used to reduce solar heat gain and combat glare.

If employers use air conditioning, they need to ensure that the system is regularly serviced and checked to ensure it is working at optimal levels at all times.

During periods of high summer temperatures, employers should encourage workers to take regular breaks.

An indoor heat stress prevention plan should be developed to handle indoor heat, which should include the following:

• hydration - employees should be encouraged to keep hydrated, and employers should provide cool water supplies in the workplace;
• information - if it is necessary for employees to work in high temperatures, they should be educated about the symptoms of heat-related illnesses and the measures they can take to protect themselves;
• clothing - if a workplace has a dress code, in hot weather it is important to assess whether there is a case for relaxing the dress code so workers can wear comfortable, lightweight clothing;
• PPE - assess the risk from wearing PPE in hot weather and whether the PPE is the most appropriate available, and whether the time spent working in PPE can be reduced;
• vulnerable workers - employers may wish to give vulnerable workers more frequent rest breaks and reduce their hours;
• manual work - workers carrying out manual work in hot conditions should have regular breaks and drink plenty of water;
• sun glare - use blinds or solar control window film to reduce sun glare on computer screens;
• first aid - make sure first aiders are aware of the symptoms of heat stress and its treatment.

What can I do?

Tips for coping in hot weather include:

• keep out of the heat if you can - if you have to go outside:
  • try to stay in the shade, especially between 11am and 3pm,
  • wear sunscreen, a hat and light clothes, and
  • avoid exercise or activity that makes you hotter;
• cool yourself down:
  • have cold food and drinks,
  • avoid alcohol, caffeine and hot drinks, and
  • have a cool shower or put cool water on your skin and clothes;
• keep your living space cool:
  • close windows during the day and open them at night when the temperature outside has gone down,
  • electric fans can help if the temperature is below 35°C, and
  • check the temperature of rooms, especially where people at higher risk live and sleep;
• keep an eye out for symptoms of heat exhaustion, and if you are concerned about these symptoms, call 111:
  • tiredness,
  • dizziness,
  • headache,
  • nausea,
  • vomiting,
  • excessive sweating and pale, clammy skin;
• keep an eye out for these symptoms of heatstroke and if suspected, call 999:
  • confusion or lack of co-ordination,
  • seizures (fits),
  • loss of consciousness,
  • high body temperature – a temperature of or above 40°C (104°F),
  • red, hot skin that can be sweaty or dry, 
  • fast heartbeat,
  • fast shallow breathing, 
  • diarrhoea.

For more information on this subject, see:

• Temperature in the workplace.