Guideline for Managing Occupant Health and Productivity in
Unconditioned Indoor Environments During High Heat Events

Adopted by the MIAQC Board of Directors on February 12, 2014

(Click HERE for PDF Version)


Document Scope & Purpose



Maine is typically identified as a cold climate state.  As a result, many of Maine’s buildings are designed to keep heat in during the winter, with secondary consideration for keeping heat out in the summer.

Several times each year, Maine experiences extreme heat events: days during which the maximum daily temperature exceeds 90 degrees F.[1]   Not all buildings in Maine have cooling systems to lower temperatures to acceptable comfort levels in hot weather, thus increasing the risk that building occupants will experience adverse health effects and reduced productivity.

This document is designed to provide building owners and facility managers with simple guidance for how to prevent heat-related illness and reduced productivity in building occupants when extreme temperatures outdoors create the potential for extreme temperatures indoors.  This document is most appropriate for use by facility managers and others in larger buildings (such as workplaces, schools, large residential or care facilities).  However, homeowners will also find the document useful when managing their own personal residential spaces.

The primary concern is for unconditioned spaces (those without summertime mechanical cooling) as well as managing spaces during emergency events (such as power outages) that prevent existing cooling systems from functioning properly.


Exposure to High Heat and Humidity Causes Illness:

The human body adapts to changing temperatures.  For example, when exposed to excessively hot and humid air on a summer day, our bodies sweat to provide cooling.  When exposed to a frosty winter morning, our bodies shiver to redirect blood from fingers and toes to keep vital organs warm.  Unfortunately, our bodies can only adapt to a narrow range of temperatures for a short period of time.[2]

Heat-related illness occurs when the body is unable to cool off in high heat environments.  Often high humidity will diminish the effectiveness of sweating.  When this occurs the body’s temperature rises rapidly.  This increase in body temperature may damage vital organs including the brain and may lead to death.  Factors that affect the body’s ability to cool include high temperatures, high humidity, physical exertion or activity from work or exercise, and health status.[3]  Health status factors include age (infants and the elderly are most susceptible); chronic health conditions such as heart disease, diabetes, and obesity; mental illness; and use of some prescription and illicit drugs or alcohol.[4]  Social factors such as poverty, homelessness, and social isolation can also put people at risk for heat illnesses in hot weather.[5]


Heat-related illness is preventable

Heat-related illness is preventable through awareness of the risks and taking action before the onset of symptoms.  Knowing who is at risk is the first step to prevent heat-related illness.  Those who are at risk, or who care for people at risk, should take extra steps to ensure they are protected from heat exposures.  The most effective way to prevent heat-related illness is to use air conditioning or find a facility that has air conditioning.  When air conditioning is not available, locating to cooler parts of the building, using shades to block heat from the sun, drinking lots of water, and limiting activity all help to reduce heat stress. Use of fans may also help when temperatures are lower than skin temperature (e.g., below approximately 95oF).[6]


Symptoms of heat-related illness

Symptoms of heat-related illness may be reviewed at the Maine Center for Disease Control’s webpage (  Symptoms of the most dangerous type of heat illness,hyperthermia (heat stroke) include a very high body temperature (103oF or greater); red, hot, dry skin, with no sweating; rapid pulse; rapid and shallow breathing; headache; dizziness; confusion; and unconsciousness. Symptoms of less severe heat illnesses include heavy sweating; fainting; nausea and vomiting; cold, pale, and clammy skin; dizziness; headache; and weakness.

Less severe heat illnesses can quickly turn into heat stroke if left untreated. Always call 911 or contact a medical professional if you suspect heat-related illnesses are occurring.

Additional information about heat-related illness is available from these sources:

·         Symptoms and Stages of Heat-Related Illnesses:
·         Impact on specific populations:
·         Protecting Workers from Heat Illness:

·         Glossary of terms:


High Heat and Humidity Impacts Learning and Worker Productivity

Numerous studies have been conducted regarding the impact of high heat and humidity on the human body and its ability to perform – both physically and mentally.

In the indoor environment, the presence of high heat and humidity can negatively impact the ability of building occupants to perform physical or mental tasks at optimal levels.  Numerous studies of the indoor environment show that both learning and worker productivity drop when the heat and humidity levels indoors rise above the optimal comfort zone.[7],[8]


Optimal Comfort Zone

It is widely accepted that the optimal thermal comfort zone for both health and performance is 68-72°F.[9]    As conditions indoors exceed this accepted optimal comfort zone, the risk of both heat-related illness and decreased learning capacity and productivity also increases.[10],[11]

Maintaining indoor conditions within the optimal thermal comfort zone will therefore maintain optimal productivity, as well as prevent conditions that lead to heat-related illness.



The following recommendations provide building owners, facility managers, and others with some basic guidance to manage building populations when temperatures indoors exceed the optimal thermal comfort zone.

Recommendation #1:  All buildings should have a heat stress policy, administered by a health and safety coordinator or team.

Buildings differ in their physical characteristics, the characteristics of the building occupants, and the procedures in place to ensure health and safety.  An established heat stress policy that identifies how and when monitoring should occur and what actions to take should be adopted as a component of a more comprehensive  environmental safety and health plan.
Recommendation #2:  Buildings should have adequately trained personnel

Ensure there are personnel in the building who are trained to recognize the symptoms of heat stress and dehydration, and who can refer building residents to medical care as needed.[12]  These personnel should also be trained in the use and application of the recommendations described in this document.
Recommendation #3:  Monitor both heat and humidity

Monitoring for temperature alone is insufficient to prevent adverse impact on building occupants   Humidity plays an increasingly critical role as temperatures rise above comfort levels.[13]
Recommendation # 4:  Conduct a heat index calculation for the indoor environment when indoor temperatures are at or exceed80oF

The heat index represents an easy-to-understand combination of temperature and humidity for evaluating the risk to human health and function.  It is broadly accepted and readily available through the National Weather Service (see and

Facility managers should use temperature and humidity readings to calculate an indoor heat index in the same way an outdoor heat index is calculated.[14]

Recommendation # 5:  Take appropriate actions at clearly identified environmental thresholds.

When indoor temperatures are below 78oF[15]

·         No action is required.

  When indoor temperatures exceed 78oF:

·         Adequately prepare for potential changes or worsening of indoor conditions by monitoring weather forecasts, advisories, and health alerts (such as those available through the National Weather Service ( and the Maine Center for Disease Control (

·         Provide adequate water, encourage occupants to drink extra water.[16],[17]

·         Provide reasonable accommodation for those at risk, as required by the Americans with Disabilities Act[18] (such as providing the precautionary measures identified in the next highest heat index threshold).

When the indoor heat index exceeds 80oF, precautionary measures should be considered:

·         Continue with the above recommendations, plus:

·         Allow for light clothing (shorts, cutoffs, or similar clothing that allows for air/water vapor movement away from the body.[19],[20]

·         Consider reduced hours of operation (e.g., limiting to the morning hours).

·         Reduce the intensity of any physical activity lasting more than 15 minutes or ensure activity is within ACGIH threshold limit values (need reference).[21]

·         Set up a cooling center within the building.[22]

When the indoor heat index exceeds 95oF:

·         Consider cancellation of operations and relocate populations to cooler environments.[23]




[1] NOAA. 2013. NOWData. Ithaca, NY: US Department of Commerce, National Oceanic and Atmospheric Administration, Northeast Regional Climate Center; 2012. Available: Accessed October 4, 2013.

[2]U.S. CDC. Extreme Heat: A Prevention Guide to Promote Your Personal Health and Safety. Centers for Disease Control and Prevention. Available: Accessed October 4, 2013.


[4]U.S. EPA. 2006. Excessive Heat Events Guidebook. EPA 430-B-06-005. U.S. Environmental Protection Agency,

Washington, DC.



[7]Mudarri, D. 2010. Public Health Consequences and Cost of Climate Change Impacts on Indoor Environments. Washington, D.C.: U.E. Environmental Protection Agency.

[8]Seppänen O., Fisk W.J., and Faulkner D.  2003. “Cost Benefit Analysis of the Night-Time Ventilative Cooling in Office Buildings.” Lawrence Berkeley National Laboratory, Berkeley, CA. Available: Accessed October 7, 2013.

[9]ASHRAE. 2010. ANSI/ASHRAE Standard 55-2010: Thermal Environmental Conditions for Human Occupancy. American Society of Heating, Refrigerating and Air-conditioning Engineers: Atlanta, GA.

[10] Kovats R. and Hajat S. 2008. Heat Stress and Public Health: A Critical Review. Annual Review of Public Health 28:29-41.

[11]Ballester J., et al. 2011. Long-term projections and acclimatization scenarios of temperature-related mortality in Europe. Nature Communications 2:358.


[12]Becker JA and Stewart LK. 2011. Heat-related illness. American Family Physician 83(11):1325-30.

[13]U.S. EPA. 2006. Excessive Heat Events Guidebook. EPA 430-B-06-005. U.S. Environmental Protection Agency,

Washington, DC.

[14]OSHA. Using the heat index: A guide for employers. U.S. Department of Labor, Occupational Safety and Health Administration. Available: Accessed October 8, 2013.

[15]The threshold of 78oF was chosen to match existing ASHRAE standards: ASHRAE. 2010. ANSI/ASHRAE Standard 55-2010: Thermal Environmental Conditions for Human Occupancy. American Society of Heating, Refrigerating and Air-conditioning Engineers: Atlanta, GA.

[16] U.S. CDC. Extreme Heat: A Prevention Guide to Promote Your Personal Health and Safety. Centers for Disease Control and Prevention. Available: Accessed October 4, 2013.

[17] OSHA. 2010. Fact Sheet: Protecting Workers from the Heat. Available: Accessed October 8, 2013.

[18]Americans with Disabilities Act(ADA) of 1990, 42 U.S.C. §§12101 et seq. (1990)

[19]Committee on School Health, American Academy of Pediatrics. 1984. Heat Stress and School Closings. Pediatrics 74(2): 313-14.

[20]ACGIH. 2012. Threshold Limit Values for Chemical Substances and Physical Agents: Heat Stress and Heat Strain. American Conference of Government Industrial Hygienists: Cincinnati, OH. pp. 202-211.


[22]U.S. EPA. 2006. Excessive Heat Events Guidebook. EPA 430-B-06-005. U.S. Environmental Protection Agency,

Washington, DC.

[23]ASHRAE Committee on School Health??