ASHRAE Position Document on Infectious Aerosols

EXECUTIVE SUMMARY
With infectious diseases transmitted through aerosols, HVAC systems can have a major effect on the transmission from the primary host to secondary hosts. Decreasing exposure of secondary hosts is an important step in curtailing the spread of infectious diseases. Designers of mechanical systems should be aware that ventilation is not capable of addressing all aspects of infection control. HVAC systems,1 however, do impact the distribution and bio-burden of infectious aerosols. Small aerosols may persist in the breathing zone, available for inhalation directly into the upper and lower respiratory tracts or for settling onto surfaces, where they can be indirectly transmitted by resuspension or fomite2 contact.

Infectious aerosols can pose an exposure risk, regardless of whether a disease is classically defined as an “airborne infectious disease.” This position document covers strategies through which HVAC systems modulate aerosol3 distribution and can therefore increase or decrease exposure to infectious droplets,4 droplet nuclei,5 surfaces, and intermediary fomites6 in a variety
of environments.

This position document provides recommendations on the following:
• The design, installation, and operation of heating, ventilating, and air-conditioning (HVAC) systems, including air-cleaning, and local exhaust ventilation (LEV) systems, to decrease the risk of infection transmission.
• Non-HVAC control strategies to decrease disease risk.
• Strategies to support facilities management for both everyday operation and emergencies.

Infectious diseases can be controlled by interrupting the transmission routes used by a pathogen. HVAC professionals play an important role in protecting building occupants by interrupting the indoor dissemination of infectious aerosols with HVAC and LEV systems.

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