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Traffic officers guiding traffic
Traffic officers may experience high temperatures during outdoor work.

Hot work environment


Some workplaces have special challenges related to high temperatures. Such workplaces are for instance outdoors in tropical and subtropical areas, such as agricultural work, road paving, outdoor construction, forestry, powerline maintenance, traffic regulation, fire fighting and mining. Also, indoor work may be related to very high temperatures, such as work in smelteries.

Smelteries are examples of workplaces with very high temperatures Iron foundries are workplaces with very high temperatures.
© G. Tjalvin


The human body has a core temperature of 37°C. To maintain this temperature the body has several mechanisms. In the brain, heat sensors are located in the hypothalamus. When temperatures exceeds 37°C they send out warning signals which causes

  • Increased blood flow in the skin to increase heat loss
  • Sweating (evaporation)

This way, the body copes with high temperature levels. Body heat balance is simply a balance between the body’s heat gain and heat loss.

Sources of heat
Air temperature, wind and humidity
Radiation from the sun, machines and processes
Muscular work

How the body loses heat

Firefighters experience high temperatures during their work Firefighters experience high temperatures during their work, due to the fire and the hard physical work they perform. © B.E. Moen

Heat stress, heat stroke

Very hot work conditions may cause serious health problems. Heat stress is the overall heat load on the body, in its mild form it is uncomfortable and may affect performance, but when it is more extreme the heat can be very dangerous and lead to heat stroke.

Heat stress symptoms
Nausea, vomiting
Fatigue, weakness
Headache, dizziness
Muscle cramps and aches

Heat stroke is a form of hyperthermia, an abnormally elevated body temperature with accompanying physical symptoms including changes in the nervous system function.

Heat stroke is a true medical emergency
that is often fatal if not
treated properly and promptly.

Heat stroke is also sometimes referred to as heatstroke or sun stroke. Severe hyperthermia is defined as a body temperature of 40ºC or higher.

Heat stroke symptoms/signs
High body temperature
No sweating
Red, hot skin with rash (tiny red spots)
Difficulty breathing
Strange behaviour, confusion
Coma, death

All workers and leaders should be aware of signs of heat stress to prevent the serious health effects from occurring. Signs of heat stress are often treated simply by moving the worker to a cool place to relax and by giving him/her water and salt.

Environmental temperature measurement

These are the four main variables that influence the degree of heat stress: Air temperature, relative humidity, radiant temperature and wind speed. These variables can be measured, but you need to have the correct instruments and you need to learn how to use them.

Wet bulb and dry bulb thermometer Wet bulb and dry bulb thermometer. © Colourbox

We can use the following instruments:

A thermometer (sometimes called dry-bulb thermometer) is used to measure air temperature in the shade. Air temperature can vary from below zero to up to about 50°C;

A wet-bulb thermometer is used to measure the humidity

A globe thermometer is used to measure radiant temperature, which can be quite different from air temperature. The thermometer’s bulb is placed in the middle of a 15 cm diameter hollow black copper sphere. The black globe absorbs radiation and warms the air inside.

An anemometer is a wind speed gauge.

There are many different expressions used for temperature, and it is necessary to know the difference between them if you read literature on this topic. You can find an overview of different expressions and definitions on temperature in the pdf-file at the download section. (Temperature Expressions).


During working hours, the temperature in all indoor workplaces must be reasonable. There’s no clear laws for minimum or maximum working temperatures, eg when it’s too cold or too hot to work. Some countries have guidelines, suggesting levels of temperature for certain types of work. For instance, a minimum of 16ºC or 13ºC is suggested for persons performing physical work. There’s no guidance for a maximum temperature limit. The risk of developing heat stroke is high at temperatures above 40ºC.


We can treat heat stress and heat stroke, but the most important is to prevent these situations at work. The main methods for prevention are the same as always in occupational health:

  • Remove the agent; eliminate or substitute
  • Reduce exposure by environmental changes
  • Personal protective equipment

If workers can avoid the heat, this is the best solution. When this is not possible, the period of heat exposure can be restricted. Personal protective equipment in this situation can be light clothing. When working outdoors, a hat for sun protection can be very important.

Woman wearing a hat while working in a field A hat is a great protection against heat stress. © G. Tjalvin

Workers who have to be exposed to hot conditions should be of good health and acclimated to the environment. In hot environments the workers should have good access to water and drinks with salt supplements. They should have possibility to take breaks out of the sun and there should be routines for changing work tasks, if possible.

Turist guides form an occupational group which is increasing in numbers in many countries. The guide below is working outdoors in the turist attraction Lalibela in Ethiopia. He needs a hat to protect him from the sun, as it can be very hot during his work. However, the hat also protects from rain showers - also common from time to time in this area.

guide.jpg Guide in Lalibela, Ethiopia.
© B. Moen

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This article is from the free online course:

Occupational Health in Developing Countries

University of Bergen