This document summarizes heat stress and provides guidance on prevention. It describes symptoms of heat-related illnesses like heat rash, heat cramps, heat exhaustion, and heat stroke. It recommends drinking water, acclimatizing to heat, monitoring temperature and humidity, wearing loose clothing, and being aware of symptoms in yourself and coworkers. The document also discusses legal requirements to take precautions against heat stress.

1. Heat StressHeat Stress
EssentialsEssentials
Occupational Health Clinics
for Ontario Workers Inc.
Prevention in Action

2. OutlineOutline
• Heat stress/strain health effects
• What you can do to prevent them
• What the law says
• Simple ways to monitor the heat

3. Symptoms: General
feeling of tiredness or
fatigue.
First Aid: Fluid
replacement and rest.
Transient Heat Fatigue:Transient Heat Fatigue:

4. First Aid: Practice good
personal hygiene; keep the
skin clean and the pores
unclogged, allow skin to
dry, wear loose clothing,
see doctor if rash persists.
Heat Rash (prickly heat)Heat Rash (prickly heat)
Symptoms: Skin becomes
reddened and may itch, feel
prickly or hurt.

5. Symptoms: Syncope means
“fainting.” First signs are
dizziness, feeling light-headed
and perhaps nauseous, then
the person may faint. Usually
occurs in the beginning of heat
stress season before the
circulation system is adapted.
First Aid: Lay victim in a cool
location horizontally with feet
elevated. If conscious, give
fluids. Treatment the same as
shock.
HeatHeat
SyncopeSyncope
(fainting)(fainting)

6. Symptoms: Cramping of either
active muscles (arms, legs) or
involuntary (usually abdominal)
muscles (or both).
First Aid: Replenish electrolytes
through drinking of fluids such
as Gator-Ade, Squincher,
PowerAde, etc-Ade. Rest in a
cool environment.
Heat Cramps:Heat Cramps:

7. Symptoms: Nausea,
dizziness, weakness
headache, blurred vision,
profuse sweating, cold/wet
(clammy) grayish skin,
unconsciousness, coma and
death.
First Aid: Place victim in a
prone position in a cool
location, administer fluids if
the victim is conscious. If
unconscious, seek medical
care or transport to a
medical emergency room.
Heat Exhaustion:Heat Exhaustion:

8. Symptoms: Chills, restlessness,
irritability, euphoria, red face
and skin, disorientation, hot/dry
skin (not always), collapse,
unconsciousness, convulsions
and death.
First Aid: Immediate,
aggressive cooling of the
victim’s body using wet cloths,
immersion into cold water or
alcohol wipes. Transport to
emergency medical facility
ASAP!
Heat Stroke:Heat Stroke:

9. Watch out for each other!Watch out for each other!
• A worker heading into a heat
stroke will no longer realize
what’s happening to him/her
• It is vital that co-workers be
able to recognize what’s
happening and intervene
• Without quick attention, the
co-worker may die!

10. Indirect Health Effects:Indirect Health Effects:
Reduced Work Performance: tired, fatigued
workers perform with reduced accuracy, efficiency
Increased Accidents: tired, fatigued workers are
more susceptible to accident and injury
Reproductive Problems: heat has been shown to
reduce both male and female fertility and can be a
problem for the fetus
Heart/Lung Strain: if you already have heart, lung,
kidney or circulatory problems; heat stress is an
added strain on your body which in severe situation
may precipitate serious episodes of acute problems

11. PredisposingPredisposing
Factors:Factors:
 very small body size
 overweight
 over 40 years old (the older
the more sensitive)
 previous heat illness
 heart disease
 high blood pressure
 diabetes
 inactivity
 physical activity
 …sooner or later we’re
all vulnerable …

12. …… with all thesewith all these
vulnerabilities who typicallyvulnerabilities who typically
gets heat stroke?gets heat stroke?
young physically fit males
and sick older people

13. S S
Cooling
evaporation
of sweat
Heat
Balance
H
H
Internal
Heat sources
muscle activity
H
External
Heat sources
hot weather
radiant heat sources

14. External heatExternal heat
source controlssource controls
• At the source
– Replace/isolate heat producing processes
– Block radiant heat with barriers (shade)
• Along the path
– Isolate worker from heat
– Air condition workplace (booth)
– Capture hot air with exhaust ventilation
External
Heat sources
hot weather
radiant heat sources
H

15. Internal sourceInternal source
controls:controls:
• At the source
– Reduce workload
• improve ergonomics,
• provide assistance,
• increase relief time
• slow down
– Provide adequate water
– Actively cool body
– Gradually acclimatize
– Ensure good nutrition and rest
Internal
Heat sources
muscle activity
H
H

16. Promoting CoolingPromoting Cooling
• Wear loose clothes that allow
sweat to evaporate easily
(cotton)
• Take internal heat sources
into account when using any
personal protective clothing
that prevents sweat from
evaporating
• Wash clothes regularly and
maintain good personal
hygiene
S
S
Cooling
evaporation
of sweat

17. Body Changes due toBody Changes due to
Acclimatization:Acclimatization:
• Gradually build up your ability to handle heat
(increase exposure time by an hour/day)
• When your body gets used to the heat
(acclimatized) your sweating becomes more
“efficient” (more sweat, quicker but with less
salt in sweat)
• blood flow to skin is reduced; more blood is
available to muscles
• heart rate more stable, heart stoke volume
increases and blood volume increases

18. See your doctorSee your doctor
• If you are having trouble
getting used to the heat
or
• If you have questions about
how heat may affect a
medical condition you have
… see your doctor!

19. Drink Water
Acclimatization does not
decrease your body’s need
for water.
Drink plenty of water!

20. What to drink:What to drink:
• Electrolyte drinks (e.g. Gatorade) are usually not
needed for typical North American diet (can be
used for first aid for cramps).
• Stay away from caffeinated carbonated, diet
drinks and alcohol as they take water out of your
body.
• Water is the best; juices and/or noncaffeine sport
drinks are also good (juices contain energy
restoring glucose).

21. Dehydration
To prevent
dehydration, take
advantage of
scheduled water
breaks!

22. How Much WaterHow Much Water
is Enough?is Enough?
• More than you want just to satisfy your thirst
• Sources of water are:
1. Fluids - 1 cup or 8 oz = 240 mL every 20 min
2. Foods - fruit & veggies are 90% water
• Why 10-15°C? … to maximize the amount you
drink (not too cold, not luke warm)
• Does it need to be delivered to the work station?
… depends on workplace logistics …

23. DehydrationDehydration
fluid loss time* effect & symptoms
(* timing may vary based on intensity of work and
heat/humidity)
0.75 L 1 hr unnoticed (at 1.5% weight loss you are
considered dehydrated)
1.5 L 2-3 hrs loss of endurance, start to feel thirsty, feel
hot, uncomfortable
2.25 L 3-4 hrs loss of strength, loss of energy, moderate
discomfort
3 L 4-5 hrs cramps, headaches, extreme discomfort
3.5-4 L 5-6 hrs heat exhaustion, nausea, faint
5+ L 7+ hrs heat stroke, collapse, unconsciousness
taken from: OH&S Canada Volume 69, Number 5, page 52, May 2000

24. You can and should replace
essential elements lost during
sweating;
Eat a balanced diet
rather than taking salt
tablets or drinking
expensive sports
drinks.
Eat Healthy

25. Cooler FansCooler Fans
• Purpose of a cooling fan is primarily to
increase the rate of sweat evaporation
but it also cools by convection if the air is
cooler than the skin
• Fan coolers may interfere with local
exhaust ventilation for contaminant
control, therefore be careful in where they
are placed and how they are pointed

26. Cooler FansCooler Fans (limitations)(limitations)
• If the relative humidity is over
75-80% the fan will no longer
increase evaporation of sweat
• The closer the air temperature
is to skin temperature (35-
36°C) the less effective the
cooling
– if the air temperature exceeds skin
temperature then the fan may
even heat up the body (like a
convection oven)!

27. Personal Protective EquipmentPersonal Protective Equipment
Special cooling vests or
ice vests have been
developed to wear under
chemical–resistant suits
(use on a case by case basis –
they may not work for everyone)

28. What’s the Law?What’s the Law?
General Duty Clause:
– 25(2)(h) “… an employer shall, … take every precaution
reasonable in the circumstances for the protection of a
worker;” taken from: OH&S Act
MOL Heath and Safety Guidelines: Heat
Stress:
– “The MOL uses the TLVs®
for Heat Stress published by
the ACGIH”.
taken from: http://www.gov.on.ca/LAB/english/hs/guidelines/gl_heat.html

29. 1. clothing OK/adjustment?
2/3a. WBGT screening/
detailed action limit
2/3b. WBGT screening/
detailed TLV®
5. job-specific controls
NONO
4. heat strain evaluation
- heart rate
- core temperature
YESYES
aboveabove
belowbelow
above or no dataabove or no data
excessiveexcessive
OKOK
belowbelow
2007
ACGIH
Heat
Stress/
Strain
TLV®
keep monitoring
general controls

30. What is a WBGT?What is a WBGT?
1. normal thermometer (dry-bulb)
2. wet-bulb thermometer
• humidity
3. globe temperature
• radiant heat
WWet BBulb GGlobe TTemp.

31. Screening WBGTScreening WBGT (in °C )(in °C )::
work
demands:
light moderate heavy very
heavy
100% work;
(breaks incl.)
28.0
31.0
25.0
28.0
not
allowed
not
allowed
75% work;
25% rest
28.5
31.0
26.0
29.0
24.0
27.5
not
allowed
50% work;
50% rest
29.5
32.0
27.0
30.0
25.5
29.0
24.5
28.0
25% work;
75% rest
29.0
32.5
29.0
31.0
28.0
30.5
27.0
30.0
Action Level
TLV®

32. How to measure heat stressHow to measure heat stress
using temperature & humidityusing temperature & humidity
1. Find a representative place
2. Find temperature and humidity on
chart and read off the Humidex
3. Take into account radiant heat (add
2° Humidex to measurement for full
sun)
4. Need to take clothing into account
(add 5° Humidex for overalls on top of
summer clothes)

33. Humidex Heat Stress ResponseHumidex Heat Stress Response
PlanPlan
Temp RH = 100% 95% 90% 85% 80% 75% 70% 65% 60% 55% 50% 45% 40% 35% 30%
47
46
45
44
43 45+
42 42-44 50
41 40-41 48
40 38-39 49 47
39 34-37 49 47 45
38 30-33 49 47 45 43
37 25-29 49 47 45 44 42
36 50 49 47 45 44 42 40
35 50 48 47 45 43 42 40 39
34 49 48 46 45 43 42 40 39 37
33 50 48 47 46 44 43 41 40 39 37 36
32 50 49 48 46 45 44 42 41 40 38 37 36 34
31 50 49 48 47 45 44 43 42 40 39 38 37 35 34 33
30 48 47 46 44 43 42 41 40 39 37 36 35 34 33 31
29 46 45 43 42 41 40 39 38 37 36 35 33 32 31 30
28 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29
27 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27
26 39 38 37 36 35 34 33 33 32 31 30 29 28 27 26
25 37 36 35 34 33 33 32 31 30 29 28 27 26 26 25
24 35 34 33 33 32 31 30 29 28 28 27 26 25
23 33 32 31 31 30 29 28 28 27 26 25
w at er as needed 32-35
warning & double w at er 40-42
alert & w at er 36-39
50% relief 45-46
25% relief 43-44
only medically supervised work
75% relief 47-49
Moderat e
Unacclimat i
zed &
Heavy
Moderat e
Acclimat iz
ed & Light
UnacclimatAct ion
50+
Temperature = 29°C
Relative Humidity = 60%
Humidex = 37°C

34. CAVEAT (warning)!CAVEAT (warning)!
never ignore symptoms
even if
measurements meet standards!

35. Why Worry AboutWhy Worry About
Heat Stress?Heat Stress?
• Heat can kill!
• Work-related heat stroke fatalities:
1990: student, second day collecting garbage
2001: bakery worker in Barrie
• If global warming is happening, heat
stress will become more important

36. August 9, 2001: Kim DouglasAugust 9, 2001: Kim Douglas
Warner Died of Heat StrokeWarner Died of Heat Stroke
• bakery worker was near the end of a 12 hour
shift on the 5th
day of a heat waver
• according to Environment Canada on August
9, 2001 outdoor temperature in Barrie is
33.4°C, and humidity was 30%; so the
outdoor humidex was 36°C
• if temperature in the bakery was estimated to
be 52°C and if the humidity inside was 10%,
then Humidex would have been 54°C

37. Heat stress death 1990 -Heat stress death 1990 -
Inquest Findings:Inquest Findings:
• Brian Freeman, arts student, on the second day on a
summer job as a garbage collector experienced a
heat stroke; died 17 days later
• He had received no training to recognize symptoms
• Heat stress measurements are too difficult to apply
and don’t take into account vulnerabilities
• Rather than relying on measurements, train workers
to enable them to self-regulate (recognize symptoms
and know how to reduce heat stress with breaks and
fluid intake)
• issues around malignant hyperthermia, a genetic
condition (1 in 200) which makes people more
susceptible to heat strain

38. Remember, when it’s hot:Remember, when it’s hot:
Heed your body! watch for
symptoms!
Ensure you’re drinking enough!
Adjust your activity level – slow
down!
Take clothing/PPE into account!