INTRODUCTION

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

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

OSHA

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

Outdoor operations

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

• 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

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.

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

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.

Thermal Strains Disorder And Health Effect

HEAT FATIGUE

HEAT CRAMPS

HEAT EXHAUSTION

HEAT STROKE

HEAT COLLAPSE

HEAT RASHES

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

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.

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

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.

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.

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.

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

• 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

• 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

• 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

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

• 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

• 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

Wet bulb globe temperature

index

• 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

• 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)

• 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.

Metabolic rate, M WBGT Reference value

Metabolic Rate class

Related to a unit skin surface areaW/m-2

Total(for a mean skin surface area of 1.8m2)W

Personacclimatised 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

What are exposure limits for

heat stress?

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)

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 Heav

y

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.

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

What are exposure limits for

working in the cold?

The recommended exposure times are based on:• Wind chill factor• Air temperature• Wind speed

The warm-up break periods are of 10 minute durationin a warm location.

The schedule assumes that "normal breaks" are takenonce every two hours.

At the end of a 4-hour period, an extended break(e.g. lunch break) in a warm location is recommended.

*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.

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