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U.S. Geological Survey Manual

SM 445-2-H CHAPTER 45

The Management of Occupational Heat Stress

Instruction:  This new chapter is added to the Occupational Safety and Health Program Requirements Handbook 445-2-H in order to provide guidance on the prevention, recognition, and treatment of heat stress and related illnesses. 

1.  Purpose.  To establish policy and procedures to moderate the effects of worker exposures to excessive heat while working in hot environments.  This policy applies to U.S. Geological Survey (USGS) employees and those who work under USGS funding or direction.

2.  References.

A.  Occupational Exposure to Hot Environments, National Institute for Occupational Safety and Health, Revised Criteria 1986. 

B.  2006 TLVs ® and BEIs ® Based on the Documentation of the Threshold Limit Values for Chemicals Substances and Physical Agents and Biological Exposure Indices, American Conference of Governmental Industrial Hygienists, 2006 edition. 

3.  Requirements.  The USGS will implement a heat-stress management program based on written procedures that include as a minimum:

A.  Identifying work locations or processes where employees may be exposed to excessive heat. 

B.  Establishing a training program to educate employees, contractors, and volunteers about the dangers of exposure to excessive heat and the measures that can be put into place to decrease the incidence or severity of heat-related illnesses.

4.  Responsibilities.

A.  Bureau Safety Manager.  The Bureau Safety Manager, working with the Regional Safety Managers, provides oversight of the heat-stress management program.

B.  Regional Safety Managers/Regional Safety Officers.

(1)  Provide regional safety program oversight and assist Collateral Duty Radiation Safety Officers in establishing programs for the management of heat stress and the prevention of heat-related illnesses. 

(2)  Assist Collateral Duty Safety Officers as required in establishing local heat-stress management programs and coordinating employee training.

C.  Managers/Supervisors.

(1)  Ensure that adequate resources are available to fully implement a heat-stress management program. 

(2)  Ensure that all employees assigned to perform strenuous work in hot environments are physically capable of safely carrying out their duties.  New employees or employees assigned to new positions which are physically demanding or might expose employees to heat stress must be medically cleared prior to assignment in these types of jobs.  Reference the Department of the Interior (DOI) Occupational Medicine Handbook located at:

(3)  Identify all work activities and locations where employees will be exposed to excessive heat.
(4)  Provide cool water to replace fluids.  If employees will be out in the heat for extended periods of time, sports drinks are recommended to replace electrolytes lost due to sweating.

(5)  Provide cool areas for rest and recovery.

(6)  Arrange work schedules so that the most strenuous work is conducted during the coolest part of the day.

(7)  Monitor all employees on the work crew to ensure they are drinking adequate quantities of fluids and are not suffering from heat stress.

(8)  Be familiar with the signs of heat-related illnesses and take appropriate action when someone exhibits signs of heat stress. (See Appendix 45-1 for a list of heat-related illnesses and recommended first aid.) 

(9)  Report any heat-related incidents in the Safety Management Information System.

D.  Collateral Duty Safety Officers.

(1)  Assist managers with establishing and implementing a heat-stress management program. 

(2)  Provide input to managers on the effectiveness of the established heat-stress management program. 
E.  Employees.

(1)  Follow the locally established heat-stress management program.

(2)  Be familiar with the hazards associated with working in a hot environment and the signs and symptoms of overexposure to heat.  (See Appendix 45-1 for a list of heat-related illnesses and recommended first aid.) 

(3)  Keep track of the local heat index or WBGT (Wet Bulb Globe Temperature) and moderate work, rest, and hydration based on the heat and humidity.
(4)  Report any heat-related illnesses to the supervisor. 

5.  Definitions.

(1)  Acclimation/acclimatization - Acclimation/acclimatization is the gradual adaptation to a different thermal environment.  A person unaccustomed to a hot environment will normally take an average of 7 to 10 days to physiologically “adjust” to the warmer temperatures. 

(2)  Heat Index - The heat index is a relationship between air temperature and either the relative humidity or the dew point.  The relationship between these measurements provides a more scientific way to identify the effects of heat.  The heat index considers both temperature and the effects of humidity which can affect the body’s ability to cool itself. 

(3)  Dew Point - The dew point of a given volume of air is the temperature to which this air must be cooled, at constant barometric pressure, for the water vapor component to condense into water, called dew.

(4)  Relative Humidity - Relative humidity is a measure of the ratio of the actual mass of water in a volume of air as compared to the amount of water the air can hold, expressed as a percent. 

Relative Humidity = actual vapor density        x 100%
                             saturation vapor density

(5)  Wet Bulb Globe Temperature (WBGT) - The WBGT is a measurement taken using an apparatus with three different types of thermometer: one measures air temperature (dry bulb), one considers the air temperature with humidity (the wet bulb), and the third is the black globe which takes into consideration the radiant energy of the sun.  They are calculated as follows:

Outdoors:  WBGT equals 0.7(natural wet bulb) + 0.2(black globe) + 0.1(dry bulb)
Indoors: WBGT equals 0.7(natural wet bulb) + 0.3 (black globe)

6.  Procedures.

(A)  Managers, working with their Regional Safety Officers and Collateral Duty Safety Program Coordinators, should establish local written procedures for employees whose working environments expose them to excessive heat.  These procedures should provide guidance on how to recognize heat-related illnesses as well as provide instructions on when to modify or curtail activities based on either the heat index or WBGT. 

There are two widely accepted methods for determining “perceived” heat. Appendix 45-2 shows the National Weather Service’s Heat Index Chart which gives some guidance on the heat categories and gives predictions as to the likelihood of heat illnesses in particular categories.  Appendix 45-3 shows a similar chart devised by the Army which uses the WBGT and gives more detailed information including work/rest regimens and water intake based on heat category.  A similar system has been published by the American Conference of Governmental Industrial Hygienists, ACGIH ®.

7.  Training.  Training must be provided to all employees whose working environments expose them to excessive heat.  The training does not need to be formal or complicated and can be provided as a written instruction via “toolbox” meetings, videotapes, or any other method that can convey the information.  Training should include the following:

(A)  The symptoms of overexposure to the heat.  Training must be provided so that employees can recognize the most common types of heat-related illnesses.  (See Appendix 45-1 for a list of heat-related illnesses and recommended first aid.)

(B)  A discussion of ways to prevent heat-related illnesses.  This discussion should address proper hydration, acclimation or acclimatization, taking periodic rest breaks, restraining from the use of alcohol, eating smaller meals, drinking water or sports drinks, and limiting or postponing certain activities when the heat index goes above a certain temperature.

(C)  Medical treatment for heat-related illnesses to include initial first aid and when to seek professional medical help for heat-related illnesses. This information is also provided in Appendix 45-1.

8.  Additional Resources.

(A)  Occupational Safety and Health Administration (OSHA) Heat Stress page:

(B)  NIOSH Heat Stress Information:


_/s/__Karen D. Baker____________________________      __February 4, 2008________________

Karen D. Baker                                                                         Date

Associate Director for Administrative Policy and Services 

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