Target Audience
The guide is intended to serve as a handy reference for
health and safety committee members, health and safety
representatives, employees, supervisors and managers.
For training sessions, the guide can serve as a practical
handout for future reference.
Summary
Heat stress is the net heat load on the body from the
combined effect of hot environmental conditions (air
temperature, radiant heat, humidity and air movment),
internal body heat due to physical activity, and clothing
requirements. Workplaces and occupations associated
with excessive heat exposure include: foundries, steel
mills, bakeries, construction sites, kitchens, grounds
maintenance, dishwashing and steaming.
Heat strain is the overall response of the body resulting
from heat stress. It can cause a wide variety of health
disorders. Heat stroke is the most serious health risk,
which can be fatal if medical attention is not available
promptly. People doing heavy physical work in hot and
humid conditions are affected more than those doing
light work.
Heat stress is largely preventable by engineering and
administrative control methods. As a last resort or in
extreme conditions, the use of personal protection is
warranted. Engineering controls are designed to
eliminate or minimize the level of heat exposure at the
source of the hazard. Administrative controls reduce
heat exposure at the worker. These measures include
establishing procedures for acclimatization of new
workers, training in safe work practices, reducing the
duration of work in hot environments and providing
plenty of drinking water. Workers and supervisors
must receive adequate training and education to be
able to recognize early symptoms of health disorders
and seek timely medical help.
Table of Contents
Introduction
Section 1. Legal Responsibilities to Prevent Heat Stress
1. Responsibilities as set out in Health
and Safety legislation ...............................................2
2. Ways of meeting responsibilities: being prepared.......3
Section 2. The Body鈥檚 Response to Hot Environments
1. The body鈥檚 heat balance ..............................................8
2. Heat exchange between the body
and the environment.................................................9
3. Effect of clothing.......................................................13
4. Other contributing factors..........................................13
Section 3. Safety and Health Concerns
1. Safety Concerns.........................................................16
2. Health Concerns
(a) Heat Strain ..........................................................16
(b) Heat-related illnesses..........................................18
Section 4 Measures of Heat Exposure
1. Measures of Occupational Heat Exposure: ..............26
The WBGT index
2. Environmental Measures of Heat Exposure..............30
Section 5 Heat Exposure Standards and Guidelines
1. Occupational exposure limits ....................................32
2. Thermal comfort guidelines for offices.....................40
Section 6. Control Measures
1. Engineering Controls.................................................42
2. Administrative Controls.............................................45
3. Personal Protection....................................................50
4. Sample Safe Work Practices......................................53
Section 7. Occupational Health and Safety Legislation.
1. Canadian Legislation .................................................58
2. US Legislation ...........................................................61
Section 8. Sources of Additional Information.
1. Canadian Government Departments with .................64
ResponsibilityOccupational Health and Safety
2. US Federal Safety and Health Agencies ...................69
Section 9. Bibliography and Internet Links 73
Section 10. Appendices
A. A summary of health hazards and ...........................78
preventive measures
B. The Humidex ............................................................79
C. Safety tips for different levels of the UV index ......81
D. Glossary ....................................................................83
E. Abbreviations ...........................................................85
F. Sample heat stress policy and checklist ...................87
G. Case histories: fatalities from occupational ............ 92
heat exposure
3. Effect of Clothing
Clothing affects heat exchange between the body and
the environment. Heavy clothing that fails to 鈥渂reathe鈥?
does not allow the body to cool off by air circulation
and sweat evaporation processes.
Cool Down by removing clothes
4. Other contributing factors
In addition to high temperature and humidity, the
effect of heat stress on the body depends on several
individual factors such as general health and lack of
acclimatization. Certain medications such as
antihistamines, cold remedies, diuretics, tranquilizers,
etc. may cause heat intolerance by decreasing sweat-
ing or increasing urination. People taking such medica-
tions must consult their doctor about their ability to
work in hot environments.
2. Environmental measures of heat exposure
Environmental measures are generally based on air
temperature and relative humidity but do not take into
account the effect of radiant heat and air movement in
the workplace. Therefore, such measures cannot be used
to determine occupational heat stress in the industry.
Two commonly used environmental measures are:
1. The Humidex; and,
2. The Heat Index.
The Humidex
Environment Canada鈥檚 Weather Service uses the
humidex as a measure of how hot people feel in outdoor
environmental conditions. The humidex gives a
combined effect of air temperature and relative humid-
ity as a single number that is intended to reflect per-
ceived heat (see Appendix B). Humidex levels can be
obtained on the Environment Canada website:
http://www.weatheroffice.ec.gc.ca/canada_e.html.
Heat Index
The US National Weather Service has developed a
Heat Index Chart to express perceived heat for different
environmental conditions of temperature and humidity.
A heat index chart is available from the National
Weather Service (NWS), the US National Oceanic
and Atmospheric Administration (NOAA).
Website:http://www.srh.noaa.gov/lzk/images/hindex1.gif.
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Recommended Rest Break Schedules for Acclimatized Workers
Wet Bulb Globe Temperature (WBGT) Index
Work Load Work Rate
Continuous 15 minutes 30 minutes 45 minutes
work rest per hour rest per hour
rest per hour
up to 25.0掳C 25.0掳C to 26.0C 28.0掳C to 30.0掳C
Heavy 26.0掳C to 28.0掳C
28.0掳C to 29.0掳C
up to 27.0掳C 27.0掳C to 28.0C 29.0掳C to 31.0掳C
Moderate
up to 30.0掳C 30.0掳C to 30.6C 31.4掳C to 32.2掳C
Light 30.6掳C to 31.4掳C
"http://www.worksafesask.ca/topics/specific_hazards/physical/heat.html
"http://www.worksafesask.ca/topics/specific_hazards/physical/heat.html
http://www.labour.gov.sk.ca/safety/thermal/hot/page%208%20.htm, and
Sources: "http://www.labour.gov.sk.ca/safety/thermal/hot/page%208%20.htm"
33
Using fans to cool off
Fans don't cool the air 鈥? they just move air around. Fans
keep you cool by increasing the rate of sweat evaporation.
Following are some helpful tips for using fans.
USE your fan in or next to a window, box fans are
the best.
USE a fan to bring cool air in from outside.
USE your fan by plugging it directly into the wall outlet.
If you need an extension cord, it should be CSA
approved and should not present a trip hazard.
DO NOT use fans if the room is closed and filled with
hot air. Blowing hot air on the body will increase the
risk of adverse health effects.
DO NOT use a fan to blow extremely hot air on yourself.
This can cause heat exhaustion to happen faster.
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4. Sample safe work practices
The following are some examples of safe work practices
for preventing heat stress.
(a) Working outdoors during prolonged heat spells
In the summer months, outdoor workers are simultane-
ously exposed to two main health hazards:
i. Heat stress as air temperature and/or humidity
increases; and,
ii. UV rays from sunlight.
Preventing health effects of heat Stress
AVOID unnecessary or unusual stressful activity.
PERFORM stressful tasks during the cooler parts of
the day (early morning or at night).
AVOID double shifts and overtime whenever possible.
Employers must not permit double shift or overtime
to workers in hot environments.
ADOPT a recommended work-rest regimen to recover
from the heat stress.
DRINK plenty of water in frequent small portions.
Employers are required to provide plenty of drinking
water in hot workplaces.
AVOID alcohol consumption. The consumption of
alcoholic drinks increases the risk of dehydration
and other heat-related illnesses.
CONSULT your doctor about potential side effects if
you are taking blood pressure control medication,
diuretics or water pills.
TAKE sufficient sleep and good nutrition for maintaining
a high level of heat tolerance.
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