This document discusses heat stress and heat-related illnesses that can affect workers. It describes how heat from the environment and physical activity can overload the body's ability to regulate temperature. Factors like temperature, humidity, air movement, clothing and metabolic heat from work influence heat stress levels. When the body can no longer maintain a stable core temperature, heat-related disorders may develop like heat cramps, heat exhaustion, heat stroke and heat rash. The document outlines various workplaces and jobs with high heat exposure risks. It also discusses heat stress indices used to assess risk and guidelines for controlling heat exposure to protect worker health and safety.

1. INTRODUCTION

2. SCENARIOS AT WORKPLACES
• Many people are exposed to heat on some
jobs, outdoors or in hot indoor environments.
• Operations involving high air temperatures,
radiant heat sources, high humidity, direct
physical contact with hot objects, or strenuous
physical activities have a high potential for
causing heat-related illness.
• Every year, thousands of workers become sick
from occupational heat exposure, and some
even die.
• These illnesses and deaths are preventable.
OSHA

3. Heat stress is the total heat burden that the body is
subjected to by both external and internal factors such as:
External
• Temperature
• Humidity
• Amount of air
movement
• Radiant temperature of
surroundings
• Clothing
Internal
• Physical activity
(metabolic heat load)
SWSA 2013

4. OSHA

5. EXAMPLE OF WORKPLACES
• iron and steel foundries
• nonferrous foundries
• brick-firing and ceramic
plants
• glass products facilities
• rubber products
factories
• electrical utilities
(particularly boiler
rooms),
• Bakeries
• confectioneries
• commercial kitchens
• Laundries
• food canneries
• chemical plants
• mining sites
• Smelters
• steam tunnels

6. Outdoor operations
• farm work
• Construction
• oil and gas well operations
• asbestos removal
• Landscaping
• emergency response operations
• hazardous waste site activitieS

7. • Workers at greater risk of heat stress include those
who are 65 years of age or older, are overweight,
have heart disease or high blood pressure, or take
medications that may be affected by extreme heat.
NIOSH

8. HEAT STRESS INDICES
• A single number which integrates the effects of the
basic parameters in any human thermal
environment such that its value will vary with the
thermal strain experienced by the person exposed
to a hot environment.
• All of the parameters* can be quantified, either by
measurement or estimation.

9. Environmental parameters
• Air temperature
• Mean radiant
temperature
• Relative humidity
• Air velocity
• Radiation
“human” factors
• Work rate (which
affects metabolic rate)
and
• Clothing level
• Whether the person is
acclimatised to hot
conditions

11. FUNCTION OF HEAT STRESS
INDICES
• provide tools for assessing hot environments and
predicting likely thermal strain on the body.
• Limit values based upon heat stress indices will
indicate when that strain is likely to become
unacceptable.
• The index value (measured or calculated) can be
used in design or in work practice to establish safe
limits.

14. Thermal Strains Disorder
And Health Effect
HEAT
FATIGUE
HEAT
CRAMPS
HEAT
EXHAUSTION
HEAT
STROKE
HEAT
COLLAPSE
HEAT
RASHES

15. Heat Stroke
• the most serious heat-related disorder.
• symptoms : i) the body's temperature rises
rapidly,
ii) the sweating mechanism fails,
iii) body is unable to cool down.
• the body temperature can rise to 106 degrees Fahrenheit
or higher within 10 to 15 minutes.
• can cause death or permanent

16. Heat Exhaustion
• the body's response to an excessive loss of the
water and salt, usually through excessive sweating.
• Workers most prone to heat exhaustion are those
that are elderly, have high blood pressure, and
those working in a hot environment.

17. Heat fatigue
• A factor : lack of acclimatization.
• The use of a program of acclimatization & training for
work in hot environments is advisable.
• Symptoms : i) impaired performance of skilled
sensorimotor, mental, or
vigilance jobs.
• no treatment for heat fatigue except remove the heat
stress before more

18. Heat Cramps
• affect workers who
sweat a lot during strenuous activity.
• This sweating depletes the body's salt and moisture
levels. - causes painful cramps.
• Heat cramps may also be a symptom of heat
exhaustion.

19. Heat Rashes
• is a skin irritation caused by excessive sweating
during hot, humid weather.
• Symptoms : Heat rash looks like a red cluster
of pimples or small blisters.
• Occur at : i) on the neck and upper chest,
ii) in the groin,
iii) under the breasts,
iv) in elbow creases.

20. Heat collapse (fainting)
• the brain does not receive enough oxygen because
blood pools in the extremities.
• As a result, the exposed individual may lose
consciousness. This reaction is similar to that of heat
exhaustion and does not affect the body's heat
balance.
• However, the onset of heat collapse is rapid and
unpredictable.
• To prevent, the worker should gradually become
acclimatized to the hot environment.

21. CONTROLLING THERMAL
EXPOSURE
• Action to take from Employers
• Schedule maintenance and repair jobs in hot areas for
cooler months.
• Acclimatize workers by exposing them for progressively
longer periods to hot work environments.
• Use relief workers or assign extra workers for physically
demanding jobs.
http://www.cdc.gov/niosh

22. • Provide cool areas for use during break periods.
• Provide cool water or liquids to workers.
• Provide heat stress training .
• Monitor workers who are at risk of heat stress.
http://www.cdc.gov/niosh

23. • Action from Workers
• Wear light-colored, loose-fitting, breathable clothing such
as cotton.
• Schedule heavy work during the coolest parts of day.
• Take more breaks in extreme heat and humidity.
• Drink water frequently. Drink enough water that you never
become thirsty. Approximately 1 cup every 15-20 minutes.
http://www.cdc.gov/niosh

24. • Be aware that protective clothing or personal protective
equipment may increase the risk of heat stress.
• Monitor your physical condition and that of your
coworkers.
http://www.cdc.gov/niosh

25. MECHANISM OF THERMAL
EXCHANGE
• The human body at rest will dissipate the heat
generated by metabolic process.
• Methods of body heat dissipation.
• Conduction
• Convection
• Evaporation
• Radiation
National Mine Safety and Health Academy

26. • Conduction is not a direct route of heat loss to the
environment for the human body most of the body is
in contact with the clothing.
• Heat rays (radiation) do not need a medium like air or
water for their transfer.
• For example, hot walls in a mine will not only warm
the mine air through convection, but also will emit
heat directly through radiation and affect persons
working in the area.
National Mine Safety and Health Academy

27. • Heat loss through evaporation can take place in the
following ways:
• sweat evaporation through almost two million sweat
glands in the skin
• saturation of the inhaled air in the lungs with water
vapor
• invisible loss of water through the skin without
involvement of the sweat glands
National Mine Safety and Health Academy

28. Wet bulb globe
temperature index

29. • The wet bulb globe temperature (WBGT) index is the
most widely used and accepted index for the
assessment of heat stress in industry
• The WBGT index is an empirical index.
• It represents the heat stress to which an individual is
exposed.
• The index was developed specifically for use in
industrial settings.
• The practicalities of an industrial application
necessitated a compromise between the requirement
for a precise index and the need to be able to easily
take controlled measurements

30. • The WBGT should be used to estimate whether or
not a problem exists, by identifying if the reference
values are exceeded by the measured values
• The WBGT-index combines three measurements:
• Natural wet-bulb temperature (tnw)
• Globe temperature (tg)
• Air temperature (ta)

31. • Inside buildings and outside buildings without
experiencing the effects of radiation from the sun
(solar load):
• WBGT = 0.7tnw + 0.3tg
• Outside buildings with solar load, or where a radiant
heat source is present indoors:
• WBGT = 0.7tnw +0.2tg +0.1ta
• The measurements are entered into the above the
equations to obtain a WBGT value.
• The WBGT value is then compared to the reference
values provided in the standard for the appropriate
metabolic rate and state of acclimation of the worker.

32. Metabolic rate, M WBGT Reference value
Metabolic
Rate class
Related to a
unit skin
surface area
W/m-2
Total
(for a mean
skin surface
area of
1.8m2)
W
Person
acclimatised to heat
°C
Person not acclimatised to
heat
°C
0 (resting) M≤65 M≤117 33 32
1 65<M≤130 117<M≤234 30 29
2 130<M≤200 234<M≤360 28 26
3 200<M≤260 360<M≤468
No sensible
air movement
25
Sensible Air
movement
26
No sensible
air movement
22
Sensible air
movement
23
4 M>260 M>468 23 25 18 20
Reference values of WBGT heat stress index related to a
maximum rectal temperature of 38°C

34. Two types of exposure limits:
• Occupational Exposure Limits
• Thermal Comfort Limits
ACGIH recommends TLVs (units of WBGT in °C).
WBGT unit takes into account environmental factors:
• Air temperature
• Humidity
• Air movement
• Solar load (heat from radiant sources)

35. ACGIH Screening Criteria for Heat Stress Exposure (WBGT values in °C)
for 8 hour work day five days per week with conventional breaks
Allocation of
Work in a
Work/Rest
Cycle
Acclimatized Action Limit
(Unacclimatized)
Light Moderate Heavy Very
Heavy
Light Moderate Heavy Very
Heavy
75-100% 31.0 28.0 -- -- 28.0 25.0 -- --
50-75% 31.0 29.0 27.5 -- 28.5 26.0 24.0 --
25-50% 32.0 30.0 29.0 28.0 29.5 27.0 25.5 24.5
0-25% 32.5 31.5 30.5 30.0 30.0 29.0 28.0 27.0
Notes:
• Assumes 8-hour workdays in a 5-day workweek with conventional breaks.
• TLVs assume that workers exposed to these conditions are adequately hydrated,
are not taking medication, are wearing lightweight clothing, and are in generally
good health.

36. Humidex and Thermal Comfort
Humidex Range
(°C)
Degrees of Comfort
20 - 29 Comfortable
30 - 39 Varying degrees of
discomfort
40 - 45 Uncomfortable
46 and Over Many types of labour must
be restricted

38. The recommended exposure times are based on:
• Wind chill factor
• Air temperature
• Wind speed
The warm-up break periods are of 10 minute duration
in a warm location.
The schedule assumes that "normal breaks" are taken
once every two hours.
At the end of a 4-hour period, an extended break
(e.g. lunch break) in a warm location is recommended.

39. *2008 TLVs and BEIs - Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. Cincinnati: American Conference
of Governmental Industrial Hygienists (ACGIH), 2008 - page 213
** Number of breaks: This
includes a normal break
after 2 hours and the
number of additional
warm-up breaks needed.

40. REFERENCE
• OSHA. https://www.osha.gov/SLTC/heatstress/
• Parsons, Kenneth C. in 42. Heat and Cold, Vogt,
Jean-Jacques, Editor, Encyclopedia of Occupational
Health and Safety, Jeanne Mager Stellman, Editor-
in-Chief. International Labor Organization, Geneva.
© 2011.
• SafeWork SA. 2013. Heat Stress Standard &
Documentation Developed for Use in the
Australian Environment.
http://www.aioh.org.au/product_pubs.asp