Heat Stress Plan

Heat Stress Plan


The purpose of this Heat Stress Plan is to protect employees from the adverse effects of heat while they are performing their job.  This not only applies to employees who work outside in the sun but also to employees who work inside buildings where there is no air-conditioning and little air movement.

Guidelines for the Wet Bulb Globe Temperature Index 

Heat stress levels will be assessed by measuring the Wet Bulb Globe Temperature Index (WBGT) which takes into account environmental factors such as humidity, wind speed, temperature, and radiant heat.  This environmental index correlates with deep body temperatures and other physiological responses to heat.

The heat stress level determined by measuring the WBGT and corresponding recommended break schedule are listed in the following table.  This break schedule is based on the 1999 American Conference of Governmental Industrial Hygienists threshold limit values.

Recommended Break Schedule for Measured WBGT and Work Load:


Heat Stress Level Break Schedule

Light Workload1


Moderate Workload2


  Continuous Work 86 80
Level I 15 Minute Break Every Hour 87 82.5
Level II 30 Minute Break Every Hour 88.5 85
Level III 45 Minute Break Every Hour 90 88







1. A light workload would be performing light hand or arm work.

2. A moderate workload would be walking about with moderate lifting and pushing.

Guidelines when WBGT is not measured:

Supervisors of evening or weekend work crews when measured WBGT is not available can use the following guidelines to judge heat stress levels and break schedule.  As always, the workload of the employee and an individual’s susceptibility to heat-related illnesses must be considered.  Common sense should prevail.

These guidelines are designed on the temperature of the ambient air as measured on a traditional thermometer and for moderate activities.  They have been calculated from an average of the ambient temperatures measured on heat stress days.

Recommended Break Schedule for Nights and Weekends When WGBT Is Not Measured:

Heat Stress Level Break Schedule Indoors Outdoors & Sunny
Level I 15 Minute Break Every Hour 90 °F 88 °F
Level II 30 Minute Break Every Hour 93 °F 90 °F
Level III 45 Minute Break Every Hour 98 °F 96 °F


Environmental Health and Safety Responsibilities

  • Monitor heat stress levels indoors and outdoors on days likely to cause heat stress.
  • Alert Facilities Management, Auxiliary Enterprises, Division of Student Affairs, Office of Sustainability, Dining Services, Custodial Services, and the Athletic Equipment Room prior to 12:00 p.m. to the level of heat stress following those measurements.  
  • Please inform the EHS Department at (269) 387-5589 if you would like to be added to the phone distribution list.
  • Send out a Twitter message through the WMU EHS account.

Departmental Responsibilities

  • Inform supervisors who in turn inform each of their employees of the occurrence of heat stress conditions and the recommended break schedule. If a heat stress level is reported it will continue at that level until dusk. 
  • On days likely to cause heat stress, schedule activities that cause a high metabolic workload or require working in an enclosed area in the early part of the day.
  • On heat stress days (WBGT reaches 82.5o F) an employee should not be working at a high metabolic rate such as occurs with pick and shovel work.  
  • Provide readily available fresh water in the work vicinity in order that the employees can frequently drink small quantities.  
  • It has been demonstrated that areas such as stairwells and hallways under certain conditions can be at a higher heat stress level than outdoor areas.  Air movement provided by fans can significantly lower the level of heat stress.
  • Ensure rapid treatment or medical evaluation for employees reporting heat-related illnesses and complete an accident injury report form.

Employee Responsibilities

  • Dress properly for the heat.  Natural-fiber clothing that is lightweight and loose-fitting is recommended for hot days.  If the work will take place outside in the sun, the clothing should be light-colored.
  • On heat stress days (WBGT reaches 82.5o F), adjust work rate to a moderate level.  Walking about with moderate lifting and pushing is an example of a moderate level of activity.
  • Drink water frequently on heat stress days.  Approximately eight (8) oz. of fresh water every twenty (20) minutes is recommended.
  • Eat regular meals and snacks to provide salt and electrolytes to replace those lost through sweating.
  • Recognize and report symptoms of heat-related illnesses.


WMU EHS Twitter Advisories


Follow WMU Environmental Health and Safety (@EHSWMU) on Twitter.  Types of messages posted by WMU Environmental Health and Safety via Twitter include general environmental, health, safety information, and heat stress level alerts.


Revised 9/2020