Summary of ASHRAE’s position document on Airborne Infectious Diseases, June 24, 2009

This summary is intended to provide the membership of the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) and other interested persons with information on the health consequences of exposure to airborne infectious disease and on the implications of this knowledge for the design, installation and operation of heating, ventilating, and air-conditioning (HVAC) systems.

Examples of airborne infectious diseases include Influenza, Mumps and Rubella

ASHRAE Recommends that:

A strategic research agenda be developed to address the role of HVAC systems in the spread of infectious disease;

This topic be included in ASHRAE’s future strategic plans;

Further research be conducted to understand how reducing the energy footprint of buildings will impact infectious disease transmission;

Further research be conducted on engineering controls to reduce the infectious disease transmission

ASHRAE’s position at the present is:

Many infectious diseases are transmitted through inhalation of airborne infectious particles termed droplet nuclei

Airborne infectious particles can be disseminated through buildings including ventilation systems

HVAC systems may contribute far more to both transmission of disease and, potentially, to the reduction of transmission risk. The addition of highly efficient particle filtration to central ventilating systems is likely to reduce the airborne load of infectious particles. This control strategy may prevent the transport of infectious agents from one area, such as patient rooms in hospitals or lobbies in public access buildings to other occupied spaces, when these areas share the same central ventilation system.

Airborne infectious disease transmissions can be reduced using dilution ventilation, specific in-room flow regimes, room pressure differentials, personalized and source capture ventilation, filtration and UVGI.

A 1959 study of influenza prevention in a Veterans Administration nursing home identified an 80% reduction in influenza in staff and patients through the use of upper-room ultraviolet germicidal irradiation (UVGI) (McLean 1961). Use of personalized ventilation systems that supply 100% outdoor air, highly-filtered, or UV disinfected air directly to the occupant-breathing zone may be another solution.

A full version of the ASHRAE Position Document can be found at: http://www.ashrae.org/aboutus/page/335 

"The health and comfort of buildings occupants is too important to leave IAQ as an after-thought in design, construction and operation,"

(Andrew Persily, Ph.D., chair of the committee that wrote the new guidance)

The Indoor Air Quality Guide: Best Practices for Design, Construction and Commissioning is a collaboration between ASHRAE, the American Institute of Architects, the Building Owners and Managers Association International, U.S. Environmental Protection Agency, the Sheet Metal and Air Conditioning Contractors of North America and the U.S. Green Building Council.

The book describes 40 strategies for achieving critical IAQ objectives related to moisture management, ventilation, filtration and air cleaning and source control. It also highlights how design and construction teams can work together to ensure good IAQ strategies are incorporated from initial design through project completion.

Here a few tips from the guide on improving IAQ in buildings:

Bring IAQ into the very earliest design discussions. Don't get stuck retrofitting the design for IAQ at the end of the process

Strictly limit liquid water penetration and condensation in the envelope, and control indoor humidity.

Where outdoor air quality is poor, use enhanced filtration and air cleaning to provide high quality ventilation air. Locate outdoor air intakes away from contaminant sources and provide the means to measure and control minimum outdoor airflows.

Select building materials and furnishings that have low contaminant emissions and don't require use of high-emitting cleaning products.

Exhaust contaminants from indoor activities as close to their source as possible.

Recognize that O&M is essential to long term IAQ, and provide the access, training and documentation needed to facilitate O&M.

Commission from design through occupancy to ensure that IAQ objectives are met.