The following information is taken from the
SECTION III: CHAPTER 4
Appendix III:4-1. Heat Stress: General
Appendix III:4-2. Heat Stress-Related
Appendix III:4-3. Measurement of Wet Bulb
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 inducing heat stress in
employees engaged in such operations. Such places include: 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, and steam tunnels.
Outdoor operations conducted in hot weather, such as construction,
refining, asbestos removal, and hazardous waste site activities,
especially those that require workers to wear semipermeable or
impermeable protective clothing, are also likely to cause heat stress
among exposed workers.
- CAUSAL FACTORS
- Age, weight, degree of physical fitness, degree of
acclimatization, metabolism, use of alcohol or drugs, and a
variety of medical conditions such as hypertension all affect
a person's sensitivity to heat. However, even the type of
clothing worn must be considered. Prior heat injury
predisposes an individual to additional injury.
- It is difficult to predict just who will be affected and
when, because individual susceptibility varies. In addition,
environmental factors include more than the ambient air
temperature. Radiant heat, air movement, conduction, and
relative humidity all affect an individual's response to heat.
- The American Conference of Governmental Industrial
Hygienists (1992) states that workers should not be permitted
to work when their deep body temperature exceeds 38°C
- Heat is a measure of energy in terms of quantity.
- A calorie is the amount of heat required to raise 1
gram of water 1°C (based on a standard temperature of 16.5 to
- Conduction is the transfer of heat between materials
that contact each other. Heat passes from the warmer material
to the cooler material. For example, a worker's skin can
transfer heat to a contacting surface if that surface is
cooler, and vice versa.
- Convection is the transfer of heat in a moving fluid.
Air flowing past the body can cool the body if the air
temperature is cool. On the other hand, air that exceeds 35°C
(95°F) can increase the heat load on the body.
- Evaporative cooling takes place when sweat evaporates
from the skin. High humidity reduces the rate of evaporation
and thus reduces the effectiveness of the body's primary
- Radiation is the transfer of heat energy through
space. A worker whose body temperature is greater than the
temperature of the surrounding surfaces radiates heat to these
surfaces. Hot surfaces and infrared light sources radiate heat
that can increase the body's heat load.
- Globe temperature is the temperature inside a
blackened, hollow, thin copper globe.
- Metabolic heat is a by-product of the body's
- Natural wet bulb (NWB) temperature is measured by
exposing a wet sensor, such as a wet cotton wick fitted over
the bulb of a thermometer, to the effects of evaporation and
convection. The term natural refers to the movement of air
around the sensor.
- Dry bulb (DB) temperature is measured by a thermal
sensor, such as an ordinary mercury-in-glass
thermometer, that is shielded from direct radiant energy
- HEAT DISORDERS AND HEALTH EFFECTS.
- HEAT STROKE occurs when the body's system of temperature
regulation fails and body temperature rises to critical levels.
This condition is caused by a combination of highly variable
factors, and its occurrence is difficult to predict. Heat stroke
is a medical emergency. The primary signs and symptoms of heat
stroke are confusion; irrational behavior; loss of consciousness;
convulsions; a lack of sweating (usually); hot, dry skin; and an
abnormally high body temperature, e.g., a rectal temperature of
41°C (105.8°F). If body temperature is too high, it causes
death. The elevated metabolic temperatures caused by a combination
of work load and environmental heat load, both of which contribute
to heat stroke, are also highly variable and difficult to predict.
If a worker shows signs of possible heat stroke, professional
medical treatment should be obtained immediately. The worker
should be placed in a shady area and the outer clothing should be
removed. The worker's skin should be wetted and air movement
around the worker should be increased to improve evaporative
cooling until professional methods of cooling are initiated and
the seriousness of the condition can be assessed. Fluids should be
replaced as soon as possible. The medical outcome of an episode of
heat stroke depends on the victim's physical fitness and the
timing and effectiveness of first aid treatment.
Regardless of the worker's protests, no employee suspected of
being ill from heat stroke should be sent home or left unattended
unless a physician has specifically approved such an order.
- HEAT EXHAUSTION. The signs and symptoms of heat
exhaustion are headache, nausea, vertigo, weakness, thirst, and
giddiness. Fortunately, this condition responds readily to prompt
treatment. Heat exhaustion should not be dismissed lightly,
however, for several reasons. One is that the fainting associated
with heat exhaustion can be dangerous because the victim may be
operating machinery or controlling an operation that should not be
left unattended; moreover, the victim may be injured when he or
she faints. Also, the signs and symptoms seen in heat exhaustion
are similar to those of heat stroke, a medical emergency.
Workers suffering from heat exhaustion should be removed from
the hot environment and given fluid replacement. They should also
be encouraged to get adequate rest.
- HEAT CRAMPS are usually caused by performing hard
physical labor in a hot environment. These cramps have been
attributed to an electrolyte imbalance caused by sweating. It is
important to understand that cramps can be caused by both too much
and too little salt. Cramps appear to be caused by the lack of
water replenishment. Because sweat is a hypotonic solution (±0.3%
NaCl), excess salt can build up in the body if the water lost
through sweating is not replaced. Thirst cannot be relied on as a
guide to the need for water; instead, water must be taken every 15
to 20 minutes in hot environments.
Under extreme conditions, such as working for 6 to 8 hours in
heavy protective gear, a loss of sodium may occur. Recent studies
have shown that drinking commercially available carbohydrate-electrolyte
replacement liquids is effective in minimizing physiological
disturbances during recovery.
- HEAT COLLAPSE ("Fainting"). In heat collapse,
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 heat
collapse, the worker should gradually become acclimatized to the
- HEAT RASHES are the most common problem in hot work
environments. Prickly heat is manifested as red papules and
usually appears in areas where the clothing is restrictive. As
sweating increases, these papules give rise to a prickling
sensation. Prickly heat occurs in skin that is persistently wetted
by unevaporated sweat, and heat rash papules may become infected
if they are not treated. In most cases, heat rashes will disappear
when the affected individual returns to a cool environment.
- HEAT FATIGUE. A factor that predisposes an individual to
heat fatigue is lack of acclimatization. The use of a program of
acclimatization and training for work in hot environments is
advisable. The signs and symptoms of heat fatigue include impaired
performance of skilled sensorimotor, mental, or vigilance jobs.
There is no treatment for heat fatigue except to remove the heat
stress before a more serious heat-related condition
- INVESTIGATION GUIDELINES.
These guidelines for evaluating employee heat stress approximate
those found in the 1992-1993 ACGIH publication, Threshold
Limit Values for Chemical Substances and Physical Agents and
Biological Exposure Indices.
- EMPLOYER AND EMPLOYEE INTERVIEWS.
- The inspector will review the OSHA 200 Log and, if possible,
the OSHA 101 forms for indications of prior heat stress
- Following are some questions for employer interviews: What
type of action, if any, has the employer taken to prevent heat
stress problems? What are the potential sources of heat? What
employee complaints have been made?
- Following are some questions for employee interviews: What
heat stress problems have been experienced? What type of
action has the employee taken to minimize heat stress? What is
the employer's involvement, i.e., does employee training
include information on heat stress? (Appendix
III:4-1 lists factors to be evaluated when
reviewing a heat stress situation, and Appendix
III:4-2 contains a follow-up
- WALKAROUND INSPECTION. During the walkaround inspection,
the investigator will: determine building and operation
characteristics; determine whether engineering controls are
functioning properly; verify information obtained from the
employer and employee interviews; and perform temperature
measurements and make other determinations to identify potential
sources of heat stress. Investigators may wish to discuss any
operations that have the potential to cause heat stress with
engineers and other knowledgeable personnel. The walkaround
inspection should cover all affected areas. Heat sources, such as
furnaces, ovens, and boilers, and relative heat load per employee
should be noted.
- WORK-LOAD ASSESSMENT.
- Under conditions of high temperature and heavy workload, the
CSHO should determine the work-load category of
each job (Table III:4-1 and Figure III:4-1).
Work-load category is determined by averaging
metabolic rates for the tasks and then ranking them:
- Light work: up to 200 kcal/hour
- Medium work: 200-350 kcal/hour
- Heavy work: 350-500 kcal/hour
- Cool Rest Area: Where heat conditions in the rest
area are different from those in the work area, the metabolic
rate (M) should be calculated using a time-weighted
average, as follows:
Equation III:4-1. Average
||time in minutes
In some cases, a videotape is helpful in evaluating work
practices and metabolic load.
FIGURE III:4-1. ACTIVITY EXAMPLES
- Light hand work: writing, hand knitting
- Heavy hand work: typewriting
- Heavy work with one arm: hammering in nails
- Light work with two arms: filing metal, planing
wood, raking the garden
- Moderate work with the body: cleaning a floor,
beating a carpet
- Heavy work with the body: railroad track laying,
digging, barking trees
|Sample Calculation: Assembly line
work using a heavy hand tool
||Intermediate value between heavy work with two arms
and light work with the body
||Add for basal metabolism
||Total: 6.0 kcal/min
Source: ACGIH 1992.
TABLE III:4-1. ASSESSMENT OF WORK
|Body position and movement
||add 0.8 for every meter (yard) rise
|Type of work
|Work: One arm
|Work: Both arms
|Work: Whole body
|* For a "standard"worker of 70
kg body weight (154 lbs) and 1.8m2
body surface (19.4 ft2).
Source: ACGIH 1992.
- SAMPLING METHODS.
- BODY TEMPERATURE MEASUREMENTS. Although instruments are
available to estimate deep body temperature by measuring the
temperature in the ear canal or on the skin, these instruments are
not sufficiently reliable to use in compliance evaluations.
- ENVIRONMENTAL MEASUREMENTS. Environmental heat
measurements should be made at, or as close as possible to, the
specific work area where the worker is exposed. When a worker is
not continuously exposed in a single hot area but moves between
two or more areas having different levels of environmental heat,
or when the environmental heat varies substantially at a single
hot area, environmental heat exposures should be measured for each
area and for each level of environmental heat to which employees
- WET BULB GLOBE TEMPERATURE INDEX.
- Wet Bulb Globe Temperature (WBGT) should be calculated using
the appropriate formula in Appendix III:4-2.
The WBGT for continuous all-day or several hour
exposures should be averaged over a 60-minute
period. Intermittent exposures should be averaged over a 120-minute
period. These averages should be calculated using the
Equation III:4-2. Average
Web Bulb Globe Temperature (WBGT)
For indoor and outdoor conditions with no solar load, WBGT
is calculated as:
For outdoors with a solar load, WBGT is calculated as
|WBGT = 0.7NWB + 0.2GT
||Wet Bulb Globe Temperature Index
||Nature Wet-Bulb Temperature
- The exposure limits in Table III:4-2 are valid for employees
wearing light clothing. They must be adjusted for the
insulation from clothing that impedes sweat evaporation and
other body cooling mechanisms. Use Table III:4-3
to correct Table III:4-2 for various kinds of
- Use of Table III:4-2 requires knowledge of the WBGT and
approximate workload. Workload can be estimated using the data
in Table III:4-1, and sample calculations are
presented in Figure III:4-1.
- MEASUREMENT. Portable heat stress meters or monitors are
used to measure heat conditions. These instruments can calculate
both the indoor and outdoor WBGT index according to established
ACGIH Threshold Limit Value equations. With this information and
information on the type of work being performed, heat stress
meters can determine how long a person can safely work or remain
in a particular hot environment. See Appendix III:4-2
for an alternate method of calculation.
TABLE III:4-2. PERMISSIBLE HEAT EXPOSURE THRESHOLD LIMIT
|75% Work, 25% rest, each hour
|50% Work, 50% rest, each hour
|25% Work, 75% rest, each hour
|*Values are in °C and °F, WBGT.
These TLV's are based on the assumption that nearly
all acclimatized, fully clothed workers with adequate
water and salt intake should be able to function
effectively under the given working conditions without
exceeding a deep body temperature of 38°C (100.4° F).
They are also based on the assumption that the WBGT of
the resting place is the same or very close to that of
the workplace. Where the WBGT of the work area is
different from that of the rest area, a time-weighted
average should be used (consult the ACGIH 1992-1993
Threshold Limit Values for Chemical Substances and
Physical Agents and Biological Exposure Indices
These TLV's apply to physically fit and acclimatized
individuals wearing light summer clothing. If heavier
clothing that impedes sweat or has a higher insulation
value is required, the permissible heat exposure TLV's
in Table III:4-2 must be reduced by the
corrections shown in Table III:4-3.
Source: ACGIH 1992.
- OTHER THERMAL STRESS INDICES.
- The Effective Temperature index (ET) combines the
temperature, the humidity of the air, and air velocity. This
index has been used extensively in the field of comfort
ventilation and air-conditioning. ET remains a
useful measurement technique in mines and other places where
humidity is high and radiant heat is low.
- The Heat-Stress Index (HSI) was developed by Belding and
Hatch in 1965. Although the HSI considers all environmental
factors and work rate, it is not completely satisfactory for
determining an individual worker's heat stress and is also
difficult to use.
TABLE III:4-3. WBGT CORRECTION FACTORS IN °C
|Summer lightweight working clothing
|Winter work clothing
|Water barrier, permeable
|*Clo: Insulation value of
clothing. One clo = 5.55 kcal/m2/hr
of heat exchange by radiation and convection for each
degree °C difference in temperature between the skin
and the adjusted dry bulb temperature.
Note: Deleted from the previous version
are trade names and "fully encapsulating suit,
gloves, boots and hood" including its clo value
of 1.2 and WBGT correction of -10.
Source: ACGIH 1992.
Ventilation, air cooling, fans, shielding, and insulation are the
five major types of engineering controls used to reduce heat stress in
hot work environments. Heat reduction can also be achieved by using
power assists and tools that reduce the physical demands placed on a
However, for this approach to be successful, the metabolic effort
required for the worker to use or operate these devices must be less
than the effort required without them. Another method is to reduce the
effort necessary to operate power assists. The worker should be
allowed to take frequent rest breaks in a cooler environment.
- The human body can adapt to heat exposure to some extent.
This physiological adaptation is called acclimatization. After
a period of acclimatization, the same activity will produce
fewer cardiovascular demands. The worker will sweat more
efficiently (causing better evaporative cooling), and thus
will more easily be able to maintain normal body temperatures.
- A properly designed and applied acclimatization program
decreases the risk of heat-related illnesses.
Such a program basically involves exposing employees to work
in a hot environment for progressively longer periods. NIOSH
(1986) says that, for workers who have had previous experience
in jobs where heat levels are high enough to produce heat
stress, the regimen should be 50% exposure on day one, 60% on
day two, 80% on day three, and 100% on day four. For new
workers who will be similarly exposed, the regimen should be
20% on day one, with a 20% increase in exposure each
- FLUID REPLACEMENT. Cool (50°-60°F) water or any cool
liquid (except alcoholic beverages) should be made available to
workers to encourage them to drink small amounts frequently, e.g.,
one cup every 20 minutes. Ample supplies of liquids should be
placed close to the work area. Although some commercial
replacement drinks contain salt, this is not necessary for
acclimatized individuals because most people add enough salt to
their summer diets.
- ENGINEERING CONTROLS.
- General ventilation is used to dilute hot air with
cooler air (generally cooler air that is brought in from the
outside). This technique clearly works better in cooler
climates than in hot ones. A permanently installed ventilation
system usually handles large areas or entire buildings.
Portable or local exhaust systems may be more effective or
practical in smaller areas.
- Air treatment/air cooling differs from ventilation
because it reduces the temperature of the air by removing heat
(and sometimes humidity) from the air.
- Air conditioning is a method of air cooling, but it
is expensive to install and operate. An alternative to air
conditioning is the use of chillers to circulate cool water
through heat exchangers over which air from the ventilation
system is then passed; chillers are more efficient in cooler
climates or in dry climates where evaporative cooling can be
- Local air cooling can be effective in reducing air
temperature in specific areas. Two methods have been used
successfully in industrial settings. One type, cool rooms, can
be used to enclose a specific workplace or to offer a recovery
area near hot jobs. The second type is a portable blower with built-in
air chiller. The main advantage of a blower, aside from
portability, is minimal set-up time.
- Another way to reduce heat stress is to increase the air
flow or convection using fans, etc. in the work area
(as long as the air temperature is less than the worker's skin
temperature). Changes in air speed can help workers stay
cooler by increasing both the convective heat exchange (the
exchange between the skin surface and the surrounding air) and
the rate of evaporation. Because this method does not actually
cool the air, any increases in air speed must impact the
worker directly to be effective.
If the dry bulb temperature is higher than 35°C (95°F),
the hot air passing over the skin can actually make the worker
hotter. When the temperature is more than 35°C and the air is
dry, evaporative cooling may be improved by air movement,
although this improvement will be offset by the convective
heat. When the temperature exceeds 35°C and the relative
humidity is 100%, air movement will make the worker hotter.
Increases in air speed have no effect on the body temperature
of workers wearing vapor-barrier clothing.
- Heat conduction methods include insulating the hot
surface that generates the heat and changing the surface
- Simple engineering controls, such as shields, can be used to
reduce radiant heat, i.e. heat coming from hot surfaces
within the worker's line of sight. Surfaces that exceed 35°C
(95°F) are sources of infrared radiation that can add to the
worker's heat load. Flat black surfaces absorb heat more than
smooth, polished ones. Having cooler surfaces surrounding the
worker assists in cooling because the worker's body radiates
heat toward them.
With some sources of radiation, such as heating pipes, it
is possible to use both insulation and surface modifications
to achieve a substantial reduction in radiant heat. Instead of
reducing radiation from the source, shielding can be used to
interrupt the path between the source and the worker. Polished
surfaces make the best barriers, although special glass or
metal mesh surfaces can be used if visibility is a problem.
Shields should be located so that they do not interfere
with air flow, unless they are also being used to reduce
convective heating. The reflective surface of the shield
should be kept clean to maintain its effectiveness.
- ADMINISTRATIVE CONTROLS AND WORK PRACTICES.
- Training is the key to good work practices. Unless all
employees understand the reasons for using new, or changing
old, work practices, the chances of such a program succeeding
are greatly reduced.
- NIOSH (1986) states that a good heat stress training program
should include at least the following components:
- Knowledge of the hazards of heat stress;
- Recognition of predisposing factors, danger signs, and
- Awareness of first-aid procedures for, and the potential
health effects of, heat stroke;
- Employee responsibilities in avoiding heat stress;
- Dangers of using drugs, including therapeutic ones, and
alcohol in hot work environments;
- Use of protective clothing and equipment; and
- Purpose and coverage of environmental and medical
surveillance programs and the advantages of worker
participation in such programs.
- Hot jobs should be scheduled for the cooler part of the day,
and routine maintenance and repair work in hot areas should be
scheduled for the cooler seasons of the year.
- WORKER MONITORING PROGRAMS.
- Every worker who works in extraordinary conditions that
increase the risk of heat stress should be personally
monitored. These conditions include wearing semipermeable or
impermeable clothing when the temperature exceeds 21°C
(69.8°F), working at extreme metabolic loads (greater than
500 kcal/hour), etc.
- Personal monitoring can be done by checking the heart rate,
recovery heart rate, oral temperature, or extent of body water
- To check the heart rate, count the radial pulse for 30
seconds at the beginning of the rest period. If the heart rate
exceeds 110 beats per minute, shorten the next work period by
one third and maintain the same rest period.
- The recovery heart rate can be checked by comparing the
pulse rate taken at 30 seconds (P1)
with the pulse rate taken at 2.5 minutes (P3)
after the rest break starts. The two pulse rates can be
interpreted using Table III:4-4.
- Oral temperature can be checked with a clinical thermometer
after work but before the employee drinks water. If the oral
temperature taken under the tongue exceeds 37.6°C, shorten
the next work cycle by one third.
- Body water loss can be measured by weighing the worker on a
scale at the beginning and end of each work day. The worker's
weight loss should not exceed 1.5% of total body weight in a
work day. If a weight loss exceeding this amount is observed,
fluid intake should increase.
- OTHER ADMINISTRATIVE CONTROLS. The following
administrative controls can be used to reduce heat stress:
- Reduce the physical demands of work, e.g., excessive lifting
or digging with heavy objects;
- Provide recovery areas, e.g., air-conditioned enclosures and
- Use shifts, e.g., early morning, cool part of the day, or
- Use intermittent rest periods with water breaks;
- Use relief workers;
- Use worker pacing; and
- Assign extra workers and limit worker occupancy, or the
number of workers present, especially in confined or enclosed
TABLE III:4-4. HEART RATE RECOVERY CRITERIA
|Heart rate recovery pattern
P1 and P3
High recovery (Conditions may require further study)
No recovery (May indicate too much stress)
- PERSONAL PROTECTIVE EQUIPMENT.
- REFLECTIVE CLOTHING, which can vary from aprons and
jackets to suits that completely enclose the worker from neck to
feet, can stop the skin from absorbing radiant heat. However,
since most reflective clothing does not allow air exchange through
the garment, the reduction of radiant heat must more than offset
the corresponding loss in evaporative cooling. For this reason,
reflective clothing should be worn as loosely as possible. In
situations where radiant heat is high, auxiliary cooling systems
can be used under the reflective clothing.
- AUXILIARY BODY COOLING.
- Commercially available ice vests, though heavy, may
accommodate as many as 72 ice packets, which are usually
filled with water. Carbon dioxide (dry ice) can also be used
as a coolant. The cooling offered by ice packets lasts only 2
to 4 hours at moderate to heavy heat loads, and frequent
replacement is necessary. However, ice vests do not encumber
the worker and thus permit maximum mobility. Cooling with ice
is also relatively inexpensive.
- Wetted clothing is another simple and inexpensive
personal cooling technique. It is effective when reflective or
other impermeable protective clothing is worn. The clothing
may be wetted terry cloth coveralls or wetted two-piece,
whole-body cotton suits. This approach to
auxiliary cooling can be quite effective under conditions of
high temperature and low humidity, where evaporation from the
wetted garment is not restricted.
- Water-cooled garments range from a hood, which cools
only the head, to vests and "long johns," which
offer partial or complete body cooling. Use of this equipment
requires a battery-driven circulating pump, liquid-ice
coolant, and a container.
Although this system has the advantage of allowing wearer
mobility, the weight of the components limits the amount of
ice that can be carried and thus reduces the effective use
time. The heat transfer rate in liquid cooling systems may
limit their use to low-activity jobs; even in
such jobs, their service time is only about 20 minutes per
pound of cooling ice. To keep outside heat from melting the
ice, an outer insulating jacket should be an integral part of
- Circulating air is the most highly effective, as well
as the most complicated, personal cooling system. By directing
compressed air around the body from a supplied air system,
both evaporative and convective cooling are improved. The
greatest advantage occurs when circulating air is used with
impermeable garments or double cotton overalls.
One type, used when respiratory protection is also
necessary, forces exhaust air from a supplied-air
hood ("bubble hood") around the neck and down inside
an impermeable suit. The air then escapes through openings in
the suit. Air can also be supplied directly to the suit
without using a hood in three ways:
- by a single inlet;
- by a distribution tree; or
- by a perforated vest.
In addition, a vortex tube can be used to reduce the
temperature of circulating air. The cooled air from this tube
can be introduced either under the clothing or into a bubble
hood. The use of a vortex tube separates the air stream into a
hot and cold stream; these tubes also can be used to supply
heat in cold climates. Circulating air, however, is noisy and
requires a constant source of compressed air supplied through
an attached air hose.
One problem with this system is the limited mobility of
workers whose suits are attached to an air hose. Another is
that of getting air to the work area itself. These systems
should therefore be used in work areas where workers are not
required to move around much or to climb. Another concern with
these systems is that they can lead to dehydration. The cool,
dry air feels comfortable and the worker may not realize that
it is important to drink liquids frequently.
- RESPIRATOR USAGE. The weight of a self-contained
breathing apparatus (SCBA) increases stress on a worker, and this
stress contributes to overall heat stress. Chemical protective
clothing such as totally encapsulating chemical protection suits
will also add to the heat stress problem.
American Conference of Governmental Industrial Hygienists (ACGIH).
1990. Documentation of the Threshold Limit Values and Biological
Exposure Indices. 6th ed. Cincinnati: American Conference of
Governmental Industrial Hygienists.
American Conference of Governmental Industrial Hygienists (ACGIH).
1992. 1992-1993 Threshold Limit Values for Chemical
Substances and Physical Agents and Biological Exposure Indices.
Cincinnati: American Conference of Governmental Industrial Hygienists.
American Industrial Hygiene Association (AIHA). 1975. Heating and
Cooling for Man in Industry. 2nd ed. Akron, OH: American Industrial
Electric Power Research Institute (EPRI). 1987. Heat-Stress
Management Program for Nuclear Power Plants. Palo Alto, CA: Electric
Power Research Institute.
Eastman Kodak Company. 1983. Ergonomic Design for People at Work.
Vol. II. Belmont, CA: Lifetime Learning Publications.
National Institute for Occupational Safety and Health. Criteria
for a Recommended Standard--Occupational Exposure to Hot
Environments. DHHS (NIOSH) Publication No. 86-113,
National Institute for Occupational Safety and Health.
Occupational Safety and Health Guidance Manual for Hazardous Waste Site
Activities. DHHS (NIOSH) Publication No. 85-115, 1985.
National Institute for Occupational Safety and Health. Standards
for Occupational Exposures to Hot Environments: Proceedings of a
Symposium. DHHS (NIOSH) Publication No. 76-100, January
National Institute for Occupational Safety and Health. Working in
Hot Environments. DHHS (NIOSH) Publication No. 86-112.
National Safety Council. 1985. Pocket Guide to Heat Stress.
Chicago, IL: National Safety Council.
Ramsey, J. D., Buford, C. L., Beshir, M.Y., and Jensen, R .C.
Effects of Workplace Thermal Conditions on Safe Work Behavior.
Journal of Safety Research 14:105-114, 1983.
Zenz, C. 1988. Occupational Medicine: Principles and Practical
Applications. 2nd ed. St. Louis, MO: Mosby Year Book, Inc.
APPENDIX III:4-1. HEAT STRESS: GENERAL
NOTE: Listed below are sample questions that the
Compliance Officer may wish to consider when investigating heat stress
in the workplace.
- Type of business
- Heat-producing equipment or processes used
- Previous history (if any) of heat-related problems
- At "hot" spots:
- Is the heat steady or intermittent?
- Number of employees exposed?
- For how many hours per day?
- Is potable water available?
- Are supervisors trained to detect/evaluate heat stress
ARE EXPOSURES TYPICAL FOR A WORKPLACE IN THIS INDUSTRY?
- Weather at Time of Review
- Air velocity
- Is Day Typical of Recent Weather Conditions?
(Get information from the
- Heat-Reducing Engineering Controls
- Ventilation in place?
- Ventilation operating?
- Air conditioning in place?
- Air conditioning operating?
- Fans in place?
- Fans operating?
- Shields or insulation between sources and employees?
- Are reflective faces of shields clean?
WORK PRACTICES TO DETECT, EVALUATE, AND PREVENT OR REDUCE HEAT
- Training program?
- Where given?
- For whom?
- Liquid replacement program?
- Acclimatization program?
- Work/rest schedule?
- Scheduling of work (during cooler parts of shift, cleaning and
maintenance during shut-downs, etc.)
- Cool rest areas (including shelter at outdoor work sites)?
- Heat monitoring program?
- Personal Protective Equipment
- Reflective clothing in use?
- Ice and/or water-cooled garments in use?
- Wetted undergarments (used with reflective or impermeable
clothing) in use?
- Circulating air systems in use?
- First Aid Program
- Trained personnel?
- Provision for rapid cool-down?
- Procedures for getting medical attention?
- Transportation to medical facilities readily available for
heat stroke victims?
- Medical Screening and Surveillance Program
- Who manages program?
- Additional Comments
(Use additional pages as needed.)
APPENDIX III: 4-2. HEAT STRESS-RELATED
ILLNESS OR ACCIDENT FOLLOW-UP.
- Describe events leading up to the episode.
- Evaluation/comments by other workers at the scene.
- Work at time of episode (heavy, medium, light)?
- How long was affected employee working at site prior to
- Medical history of affected worker, if known.
- Appropriate engineering controls in place?
- Appropriate engineering controls in operation?
- Appropriate work practices used by affected employee(s)?
- Appropriate personal protective equipment available?
- Appropriate personal protective equipment in use?
- Medical screening for heat stress and continued surveillance for
signs of heat stress given other employees?
- Additional comments regarding specific episode(s): (Use additional
pages as needed.)
APPENDIX III: 4-3. MEASUREMENT OF WET BULB
Measurement is often required of those environmental factors that
most nearly correlate with deep body temperature and other physiological
responses to heat. At the present time, the Wet Bulb Globe Temperature
Index (WBGT) is the most used technique to measure these environmental
factors. WBGT values are calculated by the following equations:
Equation III:4-4. Indoor or
Outdoor Wet Bulb Gobe Temperature Indexes (WBGI)
Indoor or outdoors with no solar load
Outdoors with solar load
|WBGT = 0.7NWB + 0.2GT +
||Wet Bulb Globe Temperature Index
||Natural Wet-Bulb Temperature
||Dry-Bulb (air) Temperature
||Globe Thermometer Temperature
The determination of WBGT requires the use of a black globe
thermometer, a natural (static) wet-bulb thermometer, and a
dry-bulb thermometer. The measurement of environmental
factors shall be performed as follows:
1. The range of the dry and the natural wet-bulb
thermometers should be -5°C to +50°C, with an accuracy of
±0.5°C. The dry bulb thermometer must be shielded from the sun and the
other radiant surfaces of the environment without restricting the
airflow around the bulb. The wick of the natural wet bulb thermometer
should be kept wet with distilled water for at least one-half
hour before the temperature reading is made. It is not enough to immerse
the other end of the wick into a reservoir of distilled water and wait
until the whole wick becomes wet by capillarity. The wick must be wetted
by direct application of water from a syringe one-half hour
before each reading. The wick must cover the bulb of the thermometer and
an equal length of additional wick must cover the stem above the bulb.
The wick should always be clean, and new wicks should be washed before
2. A globe thermometer, consisting of a 15 cm (6-inch) in diameter
hollow copper sphere painted on the outside with a matte black finish,
or equivalent, must be used. The bulb or sensor of a thermometer (range -5°C
to +100°C with an accuracy of ±0.5°C) must be fixed in the center of
the sphere. The globe thermometer should be exposed at least 25 minutes
before it is read.
3. A stand should be used to suspend the three thermometers so that
they do not restrict free air flow around the bulbs and the wet-bulb
and globe thermometer are not shaded.
4. It is permissible to use any other type of temperature sensor that
gives a reading similar to that of a mercury thermometer under the same
5. The thermometers must be placed so that the readings are
representative of the employee's work or rest areas, as appropriate.
Once the WBGT has been estimated, employers can estimate workers'
metabolic heat load (see Tables III:4-1 and III:4-2) and use the ACGIH
method to determine the appropriate work/rest regimen, clothing, and
equipment to use to control the heat exposures of workers in their
Heat Stress - Cool Draft Specifications
Heat Stress Infomation from OSHA Technical Manual
Heat Stress Management
Portable Drinking System