Heat Stress Guide for Employers

“Heat related illnesses are preventable with the right tools and controls. At TSI®, our QUESTemp° Heat Stress Monitors are designed to quickly and accurately evaluate potential heat stress environments. These instruments deliver high-performance monitoring using Wet Bulb Globe Temperature (WBGT) sensing technology and the calculation of a WBGT Index value, the standard for heat stress management.”  Jason Rutz, Global Product Manager, TSI, Jason.Rutz@tsi.com, 800-680-1220, TSI.com 


OSHA does not have a specific standard that covers working in hot environments. Nonetheless, under the OSH Act, employers have a duty to protect workers from recognized serious hazards in the workplace, including heat-related hazards. The Heat Index: A Guide for Employers was created to help employers and worksite supervisors prepare and implement hot weather plans. This guide explains how to use the heat index to determine when extra precautions are needed at a worksite, with the goal to protect workers from environmental contributions to heat-related illness.

Why Standard is Important

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Outdoor workers exposed to hot and humid conditions can be at risk of heat-related illness. The risk of heat-
related illness becomes greater as the weather gets hotter and more humid. The combination of both air temperature and humidity affect how hot outdoor workers feel in hot-weather conditions. 

Employers need to take into consideration the “heat index,” which is a single value that takes both temperature and humidity into account. The higher the heat index, the hotter the weather feels. The heat index is considered a better measure than air temperature alone for estimating the risk to workers from environmental heat sources.

  • NOAA issues extreme-heat advisories to indicate when excessive, extended heat will occur. The advisories are based mainly on predicted heat index values: 
  • Excessive Heat Outlook: issued when the potential exists for extended excessive heat (heat index of 105-110°F) over the next 3-7 days. This is a good time to check on supplies, such as extra water coolers, and refresh worker training. 
  • Excessive Heat Watch: issued when excessive heat could occur within the next 24-72 hours, but the timing is uncertain. 
  • Excessive Heat Warning: issued when the heat index will be high enough to be life-threatening in the next 24 hours. This warning indicates that the excessive heat is imminent or has a very high probability of occurring. 
  • Excessive Heat Advisory: similar to an Excessive Heat Warning, but less serious. This is issued when the heat index could be uncomfortable or inconvenient but is not life-threatening if precautions are taken.

Key Compliance Requirements

Extra measures, including implementing precautions at the appropriate risk level, are necessary for reducing the risk of heat stress for employees working outdoors in extreme heat. The employer’s response at the four risk levels is the subject of the remainder of OSHA’s guidelines. The steps employers should take in response to an elevated heat index are the same type of steps that they would follow to address other hazards in the workplace:

  • Develop an illness-prevention plan for outdoor work based on the heat index.
  • Train your workers how to recognize and prevent heat-related illness. Train workers about safe work practices before heat index levels go up. Workers should be prepared, so they recognize the signs and symptoms of heat-related illness; how to prevent it; and what to do if someone is demonstrating symptoms. 
  • Track the worksite heat index daily; communicate it and the required precautions to workers. Knowing how hot it will be during scheduled work activities can help to determine which preventive measures should be taken in preparation.
  • Implement your plan; review and revise it throughout the summer.

It is suggested that workers are trained before hot outdoor work begins, and training can be more effective if it is matched to job tasks and conditions and is reviewed and reinforced throughout hot weather conditions. The following OSHA-suggested training topics might be addressed in one session or in a series of shorter sessions:

  • Risk factors for heat-related illness
  • Different types of heat-related illness, including how to recognize common signs and symptoms
  • Heat-related illness prevention procedures
  • Importance of drinking small quantities of water often
  • Importance of acclimatization; how it is developed; and how your worksite procedures address it
  • Importance of immediately reporting signs or symptoms of heat-related illness to the supervisor
  • Procedures for responding to possible heat-related illness
  • Procedures to follow when contacting emergency medical services
  • Procedures to ensure that clear and precise directions to the worksite will be provided to emergency medical services 


  • You can find more about information about heat stress at Using the Heat Index: A Guide for Employers https://bit.ly/34v0nYJ or, for training documents, you can visit https://bit.ly/2M6Eto9. 

OSHA’ Critical Actions for Heat Risk

According to OSHA*, the most critical actions employers should take to help prevent heat-related illness at each risk level:

Heat Index: <91°F

Risk Level: Lower-Caution

Suggested Measures: 

  • Provide drinking water
  • Ensure that adequate medical services are available
  • Plan ahead for times when heat index is higher, including worker heat-safety training
  • Encourage workers to wear sunscreen
  • Acclimatize workers

If workers must wear heavy protective clothing, perform strenuous activity or work in the direct sun, additional precautions are recommended to protect workers from heat-related illness.

Heat Index: 91°-103°F

Risk Level: Moderate

Suggested Measures: 

In addition to the steps listed above:

  • Remind workers to drink water often (about four cups/hour)
  • Review heat-related illness topics with workers: how to recognize heat-related illness; how to prevent it; and what to do if someone gets sick
  • Schedule frequent breaks in a cool, shaded area
  • Acclimatize workers
  • Set up buddy system/instruct supervisors to watch workers for signs of heat-related illness

If workers must wear heavy protective clothing, perform strenuous activity or work in the direct sun, additional precautions are recommended to protect workers from heat-related illness.

  • Schedule activities at a time when the heat index is lower
  • Develop work/rest schedules

Monitor workers closely

Heat Index: 103°-115°F

Risk Level: High

Suggested Measures: 

In addition to the steps listed above:

  • Alert workers of high-risk conditions
  • Actively encourage workers to drink plenty of water (about four cups/hour)
  • Limit physical exertion (e.g., use mechanical lifts)
  • Have a knowledgeable person at the worksite who is well-informed about heat-related illness and able to determine appropriate work/rest schedules
  • Establish and enforce work/rest schedules
  • Adjust work activities (e.g., reschedule work, pace/rotate jobs)
  • Use cooling techniques
  • Watch/communicate with workers at all times

When possible, reschedule activities to a time when heat index is lower

Heat Index: >115°F

Risk Level: Very High-Extreme

Suggested Measures: 

Reschedule non-essential activity for days with a reduced heat index or to a time when the heat index is lower

Move essential work tasks to the coolest part of the work shift; consider earlier start times, split shifts, or evening and night shifts.

Strenuous work tasks and those requiring the use of heavy or non-breathable clothing or impermeable chemical protective clothing should not be conducted when the heat index is at or above 115°F.

If essential work must be done, in addition to the steps listed above:

  • Alert workers of extreme heat hazards
  • Establish water drinking schedule (about four cups/hour)
  • Develop and enforce protective work/rest schedules
  • Conduct physiological monitoring (e.g., pulse, temperature, etc.)

Stop work if essential control methods are inadequate or unavailable.

*This chart is available online at http://www.osha.gov/SLTC/heatillness/heat_index/.

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