Heat Stress : NS Labour and Advanced Education, Health and Safety

Date of Issue: July 01, 2002

Hazard Summary

We all enjoy the hot days of summer, but care needs to be taken when we are physically active on those days.  Physical exertion on hot and humid days may make us susceptible to the risk of Heat Stress.  Care also needs to be taken indoors in areas of high temperature.

What is Heat Stress?

Heat stress is the build up of heat in the body to the point where the body's thermostat has difficulty maintaining normal internal body temperature. When the body is unable to cool itself through sweating, serious heat illnesses may occur.  The most severe heat induced illnesses are heat exhaustion and heat stroke.  If actions are not taken to treat heat exhaustion, the illness could progress to heat stroke and possible death!

What causes Heat Stress?

Generally speaking: High Temperature+High Humidity+Physical Work=Heat Stress .

While heat stress is commonly associated with warm weather, it can occur any time the temperature is above normal (working in a boiler room for example).  Some factors involved in causing heat stress are:

  • high humidity,
  • high temperature,
  • low movement of air,
  • high radiant temperature of surroundings (hot machinery),
  • high level of physical activity,
  • low degree of physical fitness,
  • age,
  • metabolism, and
  • medical conditions and medicines.

It is difficult to predict just who will be affected and when, because individual susceptibility varies.  It is important to recognize the symptoms of heat stress disorders and take immediate and appropriate remedial actions.

What are the results of Heat Stress?

Listed from least to most serious

Results of Heat Stress
Heat Disorder Health Effects
Heat Fatigue Signs include impaired performance of skills, mental concentration, or vigiliance.  Generally due to not being used to working in heat. No treatment except to remove the person from the heat before more serious conditions develop.
Heat Rashes Most common problem.  Prickly heat rash shows itself as red bumps normally where clothing is restrictive or chafes. As sweating increases the bumps begin to feel prickly. Prickly heat occurs in skin that is persistently wet from unevaporated sweat. Rash may become infected if not careful.  In most cases heat rash will disappear when the individual returns to a cooler environment.
Heat Collapse In a collapse or faint, the brain does not receive enough oxygen because blood pools in the extremities.  The individual may lose consciousness.  The onset of collapse is rapid and unpredictable. Move to cooler area, loosen clothing, give fluids.
Heat Cramps Usually caused by performing hard physical labour in a hot environment.   Cramps are caused by the lack of water - note: excess salt can build up in the body if water lost through sweating is not replaced; do not use salt pills.  Thirst cannot be relied on as a guide to need for water.  Water must be taken every 15 to 20 minutes in hot environments - avoid alcohol, coffee, tea, carbonated drinks (pop).
Heat Exhaustion Signs are headache, nausea, dizziness, blurred vision, weakness, giddiness, thirst. Skin is damp and looks muddy or flushed.  Fortunately, this condition responds readily to prompt treatment.  Symptoms in heat exhaustion are similar to heat stroke - a medical emergency.  People suffering from heat exhaustion should be removed from the hot environment, given fluids, loosen clothing, shower or sponge bath with cool water and rest in a cool place.
Heat Stroke Occurs when the body's system of temperature regulation fails and body temperatures rise to critical levels.  The condition is caused by a combination of highly variable factors and is difficult to predict.  This is a medical emergency.   Primary signs and symptoms of heat stroke are confusion, irrational behaviour, loss of consciousness, convulsions, hot dry skin, lack of sweating (usually), and an abnormally high body temperature.  If body temperature is too high it causes death.  The elevated metabolic temperatures caused by a combination of work load and environmental heat load are also highly variable and difficult to predict.

Above Table based on OSHA Technical Manual, Section III:Chapter 4 Heat Stress - http://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_4.html

What Can I Do?

Whether at home or at work:

Controlling the heat load Guard against heat illness
Work in ventilated areas. All workplaces should have good general ventilation as well as spot cooling in hot work areas Drink cool water in small amounts frequently, one cup every 20 minutes - even when you are not feeling thirsty. Avoid alcohol, coffee, tea and caffeinated soft drinks which cause dehydration
Do not use fans when the thermometer reads 35o Celsius as this actually can increase the heat load Make water supply easily accessible, place closer to work area
Take regular rest breaks, increase frequency in times of higher temperature and humidity. Short, frequent work-rest cycles are best Ask how workers are feeling. Supervisors should monitor workplace temperature and humidity and check workers' condition. Allow workers to stop their work if they become extremely uncomfortable.
During breaks rest in an air conditioned area if possible, or at least in shaded areas Employees and employers should learn to spot signs of heat stroke.   Get emergency medical attention if someone has one or more of these symptoms: mental confusion or loss of consciousness, flushed face, hot dry skin or has stopped sweating.
Turn off heat generating equipment that's not being used Train first-aid workers to recognize and treat signs of heat stress; be sure all workers know who is trained to give first-aid.
Schedule more physically demanding tasks in the cooler times of the day Reduce work for anyone at risk.  Employers should use common sense in determining fitness for work in hot environments. Some factors to consider: age, poor conditioning, pregnancy, previous heat injuries, certain medical conditions, lack of acclimatization.
Rotate people through hot, heavy demand jobs, if possible Check with your doctor for medical conditions - heart conditions and diabetes can increase the risk of injury from heat exposure.
Pay special attention to person having to wear impermeable clothing - rubber aprons, or full body protective wear - they may be at risk at temperatures of 21o Celsius or over Avoid eating heavy meals before working in the heat
Where possible wear lightweight, light-coloured, loose fiting clothing. Use sunscreen and wear a hat when working outdoors In general regular exercise and improving fitness will help reduce risk of heat illnesses

If you believe you may be subject to heat stress at your workplace notify your supervisor. Like all health and safety issues, if the supervisor does not respond to your concern to your satisfaction raise the issue with the joint occupational health and safety committee or representative, if any; or contact the OHS Division for investigation. Ultimately, as a last resort, you may refuse to work in the conditions if you believe there is a hazard of heat stress.

Note: Working in hot conditions is governed by the Occupational Health Regulations.  Criteria for working in heat related conditions are a difficult item to measure requiring specialized equipment.  It is recommended that factors related to  heat stress be measured professionally.  Consultants who offer this service may be found by on our Consultant's List

I work in an office; are there guidelines?

There is a Humidex chart that can be used as a guideline for working in an office environment. The humidex combines the temperature and humidity into one number to reflect the perceived temperature. Further information on Heat, Humidity and the Humidex may be found at http://www.ccohs.ca/oshanswers/phys_agents/humidex.html

Also CSA Standard Z412-00 “Guideline on Office Ergonomics” section 6.6.2 defines parameters for thermal comfort.

For a practical guide (pdf) to the UV index click on http://www.who.int/uv/publications/en/GlobalUVI.pdf

In summation - caution should be used when working in hot conditions.   Remember that even at lower temperatures but with high humidity there is a risk of heat illnesses; and pay particular attention to persons performing strenuous physical labour.