Providing ventilation for health care and related facilities was discussed. Ventilation standards for health care facilities recommended by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) and other organizations were discussed. The ASHRAE standards were based on specifying a specific cubic feet per minute (cfm) flow rate of outdoor air per person for various occupied spaces in hospitals and similar facilities except in autopsy rooms where the standards are based on cfm per square foot of floor area. For most hospital spaces, air exchange rates of 5 and 25 air changes per hour (ACH) for outdoor and total air, respectively, are recommended. The 1987 standards proposed by the American Institute of Architects were 3 and 15ACH for outdoor and total air, respectively. Most research has investigated ventilation and air distribution patterns in operating rooms. Other research efforts have been directed at establishing criteria for controlling the risk of airborne infection from microorganisms. Infectious aerosols, even those of respirable size, can be removed from the air by medium to high efficiency filters. Even well filtered recirculated air can contain contaminants such as noxious gases and vapors, some originating from outdoor sources and some from occupants in inhabited areas. A discussion of health risks associated with ventilation systems included a description of the Wells Riley equation which is used for predicting the risks from inhaling infectious droplet nuclei. It was noted that infectious organisms can be produced within ventilation systems as a result of accumulations of biological materials and organic nutrients. Toxic chemicals used as biocides can also be unwittingly introduced into ventilation systems. Health risks associated with heating, ventilating, and air conditioning (HVAC) systems were discussed. Features that increase the probability of HVAC systems becoming a source of contamination include poor access to components, low efficiency filters, flat condensate pans with side drain connections, and inadequate provision for humidity control. Improper operation of HVAC systems can also introduce contaminants into the inside air.
Proceedings of the Workshop on Engineering Controls for Preventing Airborne Infections in Workers in Health Care and Related Facilities, July 14-16, 1993, Cincinnati, Ohio