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The Development and Validation of Procedures 
for Working in Hot Environments
By: Joseph A. Cocciardi, MS, CSP
Many workers spend time in hot environments during their working days. The human body maintains a fairly constant internal temperature, even though it is exposed to varying degrees of environmental heat.

To maintain body safety, the body must rid itself of excess heat, primarily through varying the rating and amount of blood circulation through the skin (as heart rates expand and blood flows closer to skin surfaces, excess heat is lost) and the release of fluid onto the skin through sweating and subsequent evaporation (cooling).  These are automatic responses.  As environmental temperatures approach normal skin temperatures cooling of the body becomes more difficult (i.e. blood brought to the body surface cannot lose its heat and sweating takes over as the primary body cooling mechanism).  During conditions of high humidity (or when sweat cannot evaporate through body coverings adequately) the body’s ability to maintain acceptable temperatures may become impaired.

Individuals work ability and alertness may also be effected.
Excessive exposure to hot work environments may induce a variety of heat related disorders such as heat stroke (the most serious health problem associated with working in hot environments and a medical emergency), heat exhaustion, heat cramps, fainting or transient heat fatigue.

There are four environmental stressors in a hot environment.  These are:

1. Temperature
2. Humidity
3. Radiant heat
4. Air velocity movement over the body surface

When these factors increase at a rate which cannot be handled by the body’s natural mechanisms for shedding heat, the physical heat disorders may occur.

This article recommends development and implementation of Heat Stress Monitoring and Safety Programs for industrial sites during times when heat related diseases can occur.  Specific programmatic recommendations are based on activities performed at an industrial cleanup site where a variety of personal protective equipment ensembles ranging from ordinary body coverings through supplied air respiratory protection systems and impervious clothing were used.  Heavy construction work was performed.  This particular industrial operation occurred during the Summer of 1997, when ambient temperatures averaged daily highs between 85oF and 92oF.


A variety of criteria documents for working in hot environments exist.  These include the U.S. Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health (NIOSH) Criteria for Recommended Standard:  Occupational Exposure to Hot Environments; The American Conference of Governmental Industrial Hygienists:  Heat Stress Recommendations, as published in Threshold Limit Values and Biological Exposure Indices for Harmful Physical Agents; the Occupational Safety and Health Administration’s Technical manual, Section II:  Heat Stress; and various components of health hazard evaluation reports such as NIOSH Report TA80-77-853:  Health Hazard Evaluation, Chemical Control Corporation, Elizabeth, New Jersey.  The key components of each of these programs are listed in Table I.



a) Work Place Limits and Surveillance
b) Medical Surveillance
c) Surveillance of Heat Induced Sentinel Health Events
d) Posting of Hazardous Areas
e) Protective Clothing and Equipment Programs
f) Worker Information and Training
g) Control of Heat Stress
h) Recordkeeping

OSHA (3)
a) Provision of Cool Rest Areas
b) Sampling of the Environment
c) Environmental Controls (ventilation, air cooling)
d) Fluid Replacement
e) Engineering Controls 
f) Administrative Controls and Work Practices (training)
g) Worker Monitoring Programs
h) Personal Protective Equipment (reflective clothing, auxiliary body cooling devices, wetted clothing, water cooled garments, circulating air)

a) Cool Off Period Provision
b) Heart Rate Monitoring
c) Body Temperature Monitoring
d) Weight Loss Monitoring
e) Environmental Surveillance Monitoring:Initiation and Recommendations

American conference of Governmental Industrial Hygienists (6)

a) Measurement of the Environment
b) Development of Work Load Categories
c) Development of Work Rest Regimen
d) Water and Salt Supplementation
e) Other Considerations:
1) Clothing
2) Acclimatization and Fitness
3) Adverse Health Effects
Typically, safety protocol for hot environments should be considered when temperatures reach 72OF (5).  Factors such as work regimen, area ventilation, ambient sunlight and worker health and fitness affect the initiation of hot environment monitoring.  As reference environmental conditions change, protocol may increase/decrease.

Additionally, time of the year, time of the day, or other environmental factors specific to sites, may affect the need for a Heat Stress Monitoring Program, as well as the acclimatization level of workers (i.e. how their bodies have been trained to compensate for heat).  At the site in question, the combination of environmental heat, environmental humidity and the workload to be performed (manual digging) in conjunction with protective equipment in excess of that used by general workers made obvious the need for a Heat Stress Monitoring Program.

As with any health and safety protocol, a Heat Stress Monitoring Program should be written.  During the specific situation reviewed, the Heat Stress Prevention Plan and Monitoring Program were part of a site Safety Plan.  Implementation and validation of the procedures occurred on-site, through axial temperature, pulse, and employee weight loss and liquid intake volume recordings.  Training and medical monitoring for workers was provided prior to the initiation of activities.

The site specific program developed included:

1. Medical pre-approval for workers by a licensed healthcare provider for workers to operate in hot environments, use personal protective equipment and certain types of body coverings.

2. Worker training, occurring the first day of the job for workers and subcontractors.

3. A hydration program, originally encouraged and later highly recommended with the need for increased liquid intake.

4. The development of an acclimatization period (developed from the documents previously stated).

After the initiation of work, physiological monitoring occurred during the acclimatization period.  Additionally, activities were moved to second shift to reduce ambient temperature exposures.  Physiological monitoring included axial pulse, radial pulse and body weight measurements before and after each regimen of work.  The purpose of the monitoring was to prohibit or restrict workers from activities in personal protective equipment if core body temperature exceeded 100.6OF as indicated by the referenced monitoring (with an adjustment for axial temperature) if heat rates (as measured by pulse) remained or returned to excessive high levels (110 bpm) at the completion of work regimens or if body weight (water) loss appeared to exceed 1.5% of total body weight/shift.  After the initiation of the project, modifications occurred to the procedure during a validation period.  These modifications included:

1. An increase in fluid intake of up to 32 ounces per work regimen and, for some workers, a recommended liquid intake increase of up to two gallons per day.

2. (While originally not included), a weighing regimen, added to the monitoring (weight loss).

3. Clocks were added for worker self review purposes at the work site.  Also, workers were taught and performed self radial pulse checks.  Through the training regimen, it was observed that workers had become aware of the heat stress monitoring protocol and began to self monitor.

Statistically, during this work event (three weeks), the following was noted:

1. Medium weight loss:  4-5 pounds per regimen.
2. Medium temperature gain:  1.9OF per regimen.
3. Radial pulse increases:  up to 42 beats per minute over baseline.
4. Fluid intake:  20 to 30 ounces per break.
5. 88OF during the regimens, average temperature.
6. Incident and accidents or sentinel health events.

During the time frame noted, the acclimatization period, which was originally intended to be three days, actually took eight days.  At the completion of the acclimatization period maximum work regimens (60 minutes of continuous work) were observed, without physiological indicators moving above recommended levels.  At those times a return to normal baselines occurred within 10 to 15 minutes.


The need for heat stress monitoring is apparent during warm and humid temperatures, in particular, during times where air velocity available for cooling/evaporation purposes is reduced due to the use of personal protective equipment.  At such times, physiological monitoring is essential.  Additional Heat Stress Monitoring Program requirements which may be applicable include hydrations and worker training and awareness.  Through modified programs, occupational health and safety personnel may develop amended heat stress work plans based upon site specific information acquired.

Note: This article has been developed from a presentation the author provided at the American Industrial Hygiene Conference and Exhibition in Atlanta, Georgia, June 1998. 


(1) Morbidity and Mortality Weekly Report, June 1998, Volume #47, #23, Page 473:  “Heat Related Mortality, U.S., 1997”, Massachusetts Medical Society, New England Journal of Medicine.

(2) The National Institute of Occupational Safety and Health, U.S. Public health Service, Centers for Disease Control and Prevention, Health Hazard Evaluation Report #TA80-77-853 (Chemical Control Corporation:  Elizabeth, NJ, April 1981).

(3) OSHA Technical Manual, Section 2, Chapter 4:  “Heat Stress”, U.S. Department of Labor, Occupational Safety and health Administration, Criteria for Recommended Standard Occupational Exposure to Hot Environments, Revised Criteria Document, U.S. Department of Health and Human Services, Public Health Service, Center for Disease Control and Prevention, National Institute for Occupational Safety and Health, April 1986.

(4) Cocciardi, J.A., “The Development and Validation of Procedures for Working in Hot Environments and Industrial Cleanup Situation During the Summer of 1997”, American Industrial Hygiene conference and Exhibition (Atlanta, GA, May 1998).

(5) Criteria for Recommended Standard…Occupational Exposure to Hot Environments, U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health (NIOSH)  [DHHS-No. 86-113], Washington, D.C., 1986.

(6) American Conference of Governmental Industrial Hygienists:  Threshold Limit Values for Chemical Substances and Physical Agents, ACGIH Worldwide:  Cincinnati, OH, 1998.

About the author: Joseph Cocciardi is the principal owner of Cocciardi and Associates, Inc. a safety, training and environmental service firm located in Mechanicsburg, PA. more...