Heat Stress in the Building Environment


The purpose of this document is to provide information regarding precautions, risk factors and symptoms of heat related illnesses, and provide guidance for supervisors on assessing when indoor environments move from the uncomfortable to the unhealthy range. This document was created in 2008 as a collaborative effort with Human Resources in case flood damage affected the ability to air condition buildings and indoor offices needed to assess heat conditions. 
This document is not for indoor environments involving heat-producing equipment or higher physical activity levels and it is not for outdoor working environments. 

Information on Heat Related Illnesses

When the body is unable to cool itself by sweating, several heat-induced illnesses such as heat exhaustion and the more severe heat stroke can occur.


  • Drink plenty of fluids. During heavy exercise or activity, two to four 16 ounce servings of cool, nonalcoholic, sugar-free fluids are recommended.
  • Replace salt and minerals. Heavy sweating removes salt and minerals from your body. A sports beverage can replace the salt and minerals lost in sweat.
  • Wear appropriate clothing and sunscreen. Choose lightweight, light-colored, loose-fitting clothing. When outdoors protect yourself from the sun by wearing a hat, sunglasses and a sunscreen of SPF 15 or higher.
  • Pace yourself. Start slowly and pick up intensity gradually. If exertion makes your heat pound and leaves you gasping for breath, STOP the activity.
  • Take care of each other. Monitor the condition of co-workers or those around you. Heat-induced illness can cause a person to become confused or lose consciousness.

Risk Factors:

Environmental conditions, activity levels, and personal factors affect thermal comfort. 
Environmental factors include airflow, temperature, humidity, and radiation from the sun and nearby hot surfaces. 
Activity levels are rated as low, medium, and high based on metabolic heat generated. Typical office work is rated as low, while construction, manual labor, or proximity to heat sources is a medium or high level for heat stress potential.
Personal factors include the type of clothing worn, and to a lesser degree, age, sex, body shape, state of health, diet, sleep, and acclimatization. The level of heat stress at which health effects occur is highly individual and depends upon the heat tolerance capabilities of each individual.  Some medical conditions and/or medications may create a higher level of risk of heat related illness, or the heat may exacerbate the existing medical condition.  Encourage staff members to talk with their supervisor or Human Resource representative if they have personal factors that may put them at higher risk of health related illness.

Heat Related Medical Conditions:

Heat exhaustion occurs when the body is dehydrated.

  • Symptoms: headaches, nausea, dizziness, cool and clammy skin, pale face, cramps, weakness, profuse perspiration.
  • First aid: move to a cooler spot, drink water, and rest.
  • It can lead to collapse and heatstroke.

Heatstroke occurs when perspiration cannot occur and the body overheats.

  • Symptoms: headache nausea, face flushed, hot and dry skin, no perspiration, body temperature of 101 degrees Fahrenheit, chills, rapid pulse
  • First aid: cool the person immediately, move to shade or indoors, wrap in a cool, wet sheet, and always get medical assistance.
  • It can lead to confusion, coma, and death.

How to Monitor Environmental Conditions

The heat index is a useful indicator of conditions ranging from uncomfortable to when effects of heat can lead to heat exhaustion or heatstroke. The full heat index chart may be viewed at NOAA’s National Weather Service website. Copied below is the portion of the chart relative to indoor environments. 

Heat Index Graphic

Guidelines for Supervisors

  • Indoor Environments in the Uncomfortable Range
  • The uncomfortable range is a heat index of 80 – 90 for average individuals.  Supervisors and staff will need to monitor the impact as the heat index rises within that range, recognizing the various factors impacting how any individual may be physically impacted.
  • Encourage use of precautions, such as light clothing, frequent breaks, water and sports drink intake, and breaks in cooler areas.
  • Most individuals will experience a range of effects depending on their personal tolerance including whether they are acclimatized (already used to being in the heat for 3-5 days) and personal risk factors (age, weight, fitness, and some medications used for blood pressure, water retention, thyroid, and mental health).
  • For individuals most impacted, consider flexible schedules, work at home or use of vacation to avoid peak temperature periods.  

Indoor Environments that are At Risk of Heat Related Illness

  • A heat index between 90 and 105 warrants additional caution, as there is an increased risk of heat related illness.  Individuals may experience muscle cramps or heat exhaustion, particularly with prolonged exposure and/or with physical activity.  
  • Increase use of precautions and options for alternate schedules and work sites become more important.  Monitor the impact of heat on individual employees closely.
  • Contact Environmental Health & Safety if the heat index approaches 90 and staff will be wearing impermeable protective clothing; staff are in close proximity to heat-producing sources such as industrial washers/dryers; activity levels include moving cargo, constant walking/use of stairs, and/or work in the sun.

Indoor Environments that are at High Risk of Heat Related Illness

  • This range begins with a heat index of 105.  Conditions at this level and above are most likely to result in heat related medical conditions.
  • For essential personnel, administrative or engineering controls will be needed, and you should contact Environmental Health & Safety for additional guidance. Examples of these activities may be wearing impermeable protective clothing or performing heavy labor in heat or humidity or with sun exposure. 

Other Resources: