July 5, 1993

                                HEAT STRESS


Produced by the Professional
and Specialized Services of the Occupational
Health and Safety Branch, Ministry of Labour.


WHAT IS HEAT STRESS?

Working or playing where it is hot puts stress on our body's cooling 
system.  When the heat is combined with other stresses such as hard 
physical work, loss of fluids, fatigue or some medical conditions, it may 
lead to heat-related illness, disability and even death.

This can happen to anybody--even if you are young and fit.  In Ontario, 
heat stress is usually a concern during the summer.  This is especially 
true early in the season, when people are not used to the heat.

HOW WE COPE WITH HEAT

Your body is always generating heat and passing it to the environment.  
The harder your body is working, the more heat it has to lose.  When the 
environment is hot or humid or has a source of radiant heat (for example, a 
furnace or the sun), your body must work harder to get rid of its heat.

If the air is moving (for example, from fans) and it is cooler than your 
body, it is easier for your body to pass heat to the environment.

Workers over 40 should be more careful because of a reduced ability to 
sweat.

CONTROLLING HEAT STRESS

Acclimatization

The longer you do hard work in the heat the better your body becomes at 
keeping cool.  If you are not used to working in the heat then you must 
take a week or two to get acclimatized or used to the heat.  If you were 
ill or away from work for a week or so you can lose your acclimatization.

There are two ways to acclimatize:

1.  If you are experienced on the job, limit your time in the hot 
    environment to 50% of the shift on the first day and 80% on the second 
    day.  You can work a full shift the third day.

    If you are not experienced on the job (for example, a summer student), 
    you should start off spending 20% of the time in the hot environment on 
    the first day and increase your time by 20% each following day. 

2.  Instead of reducing the exposure times to the hot job, you can become 
    acclimatized by reducing the physical demands of the job for a week or 
    two. 

If you have health problems or are not in good physical condition, you may 
need longer periods of acclimatization.

Hot spells in Ontario seldom last long enough to allow acclimatization.  
When it is hot, consider some of the following engineering and 
administrative controls.

Modifying work and the environment

Management and the Joint Health and Safety Committee can reduce heat stress 
in the following ways:

Engineering Controls

-  Control the heat at source through the use of insulating and reflective 
   barriers (insulate furnace walls).

-  Exhaust hot air and steam produced by specific operations.

-  Reduce the temperature and humidity through air cooling.

-  Provide air-conditioned rest areas.

-  Increase air movement if temperature is less than 35 deg C (fans).

-  Reduce physical demands of work task through mechanical assistance 
   (hoists, lift-tables, etc.).

Administrative Controls

-  Health and safety committees should assess the demands of all jobs and 
   have monitoring and control strategies in place for hot days.

-  Increase the frequency and length of rest breaks.

-  Schedule hot jobs to cooler times of the day.

-  Provide cool drinking water near workers and remind them to drink a cup 
   every 20 minutes or so.

-  Workers should salt their food well, particularly while they are 
   acclimatizing to a hot job (workers will a low salt diet should discuss 
   this with their doctor). 

-  Assign additional workers or slow down work pace.

-  Make sure everyone is properly acclimatized.

-  Train workers to recognize the signs and symptoms of heat stress and 
   start a 'buddy system' since people are not likely to notice their own 
   symptoms. 

-  Pregnant workers and workers with a medical condition should discuss 
   working in the heat with their doctor.

Personal Protective Equipment

-  Light summer clothing should be worn to allow free air movement and 
   sweat evaporation. 

-  Outside, wear light-coloured clothing.

-  In a high radiant heat situation, reflective clothing may help.

-  For very hot environments, air, water or ice-cooled insulated clothing 
   should be considered.

-  Vapour barrier clothing, such as acid suits, greatly increases the 
   amount of heat stress on the body, and extra caution is necessary.

The Ministry of Labour uses the Threshold Limit Values for Heat Stress 
published by the American Conference of Governmental Industrial 
Hygienists.  These values are based on preventing fit, acclimatized 
workers' core temperatures from rising above 38 deg C.

If you have questions about heat stress or how to measure it after 
reading this guide, call a Ministry of Labour office.  For more 
technical information, ask for the Ergonomist or Hygienist.


                            HEAT STRESS HAZARDS

Heat Rash

Cause:       Hot humid environment; plugged sweat glands.
Symptoms:    Red bumpy rash with sever itching.
Treatment:   Change into dry clothes and avoid hot environments.  Rinse 
             skin with cool water.
Prevention:  Wash regularly to keep skin clean and dry. 

Sunburn

Cause:       Too much exposure to the sun.
Symptoms:    Red, painful, or blistering and peeling skin.
Treatment:   If the skin blisters seek medical aid.  Use skin lotions 
             (avoid tropical anaesthetics) and work in the shade.
Prevention:  Work in the shade; cover skin with clothing; wear suntan 
             lotions with a sun protection factor of at least 15.  People 
             with fair skin should be especially cautious. 

Heat Cramps

Cause:       Heavy sweating drains a person's body of salt, which cannot be 
             replaced just by drinking water.
Symptoms:    Painful cramps in arms, legs or stomach which occur suddenly 
             at work or later at home.  Cramps are serious because they can 
             be a warning of other more dangerous heat-induced illnesses. 
Treatment:   Move to a cool area; loosen clothing and drink cool salted 
             water (1 tsp. salt per gallon of water) or commercial fluid 
             replacement beverage.  If the cramps are severe or don't go 
             away, seek medical aid.
Prevention:  When working in the heat, workers should put salt on their 
             food (if on a low-salt diet, this should be discussed with a 
             doctor).  This will give the body all the salt it needs; don't 
             take salt tablets.

Fainting

Cause:       Not enough blood flowing to the head, causing loss of 
             consciousness.
Symptoms:    Sudden fainting after at least two hours of work; cool moist 
             skin; weak pulse.
Treatment:   Fainting may be due to a heart attack or other illness.  GET 
             MEDICAL AID.  Assess need for CPR.  Move to a cool area; 
             loosen clothing; make person lie down; and if the person is 
             conscious, offer sips of cool water. 
Prevention:  Reduce activity levels and/or heat exposure.  Drink fluids
             regularly.  Workers should check on each other to help spot 
             the symptoms which often precede heat stroke.

Heat Exhaustion

Cause:       Inadequate salt and water intake causes a person's body's 
             cooling system to start to break down.
Symptoms:    Heavy sweating; cool moist skin; body temperature over 
             38 deg C; weak pulse; normal or low blood pressure; person is 
             tired, weak, clumsy, upset or confused; is very thirsty; or is 
             panting or breathing rapidly, vision may be blurred.
Treatment:   GET MEDICAL AID.  This condition can lead to heat stroke, 
             which can kill.  Move the person to a cool shaded area; loosen 
             or remove excess clothing; provide cool water to drink (salted 
             if possible); fan and spray with cool water. 
Prevention:  Reduce activity levels and/or heat exposure.  Drink fluids
             regularly.  Workers should check on each other to help spot 
             the symptoms which often precede heat stroke.

Heat Stroke

Cause:       If a person's body has used up all its water and salt, it will 
             stop sweating.  This can cause body temperature to rise.
Symptoms:    High body temperature (over 41 deg C) and any one of the 
             following: the person is weak, confused, upset or acting 
             strangely; has hot, dry, red skin; a fast pulse; a headache or 
             dizziness.  In later stages, a person may pass out and have 
             convulsions.
Treatment:   CALL AMBULANCE.  This condition can kill a person quickly.
             Remove excess clothing; fan and spray the person with cool 
             water; offer sips of cool water if the person is conscious.
Prevention:  Reduce activity levels and/or heat exposure.  Drink fluids
             regularly.  Workers should check on each other to help spot
             the symptoms which often precede heat stroke.