IAQ in health care settings
Air and ventilation requirements
Operating rooms, protective environment rooms, and burn units are required by the standard to have Type E, non-aspirating air devices located in the ceiling. These are typically laminar flow diffusers. Nonlaminar flow diffusers can entrain room air into their supply pattern and potentially carry airborne bacteria toward the patient. The diffusers should be located directly over the patient and the return or exhaust should be located away from the patient with two devices at or near floor level located diagonally opposite to maintain the laminar airflow.
Outdoor air usually contains very low densities of airborne bacteria. If the air handling unit’s outdoor air intake is located away from sources of contamination and is well maintained, the use of outdoor air ventilation to reduce concentrations of airborne bacteria indoors can be effective. Unfortunately, there is little empirical data showing the relationship between ventilation rates and infection rates.
Because the capital costs and energy costs to heat and cool outdoor air can be high, it is expected that the next release of Standard 170 will reduce some of the air change rates of outdoor air that have been used traditionally.
When the total air circulation rate is increased and the air handling system is equipped with high-efficiency filters, the filters will remove more airborne bacteria from the airstream. There is some theoretical research, mostly on surgical settings, showing a potential for reduction in airborne particle counts and associated surgical site infections. There is very little empirical evidence to show a linkage between increased total ventilation rates and decreased infection rates. In fact, there is actually clinical trial evidence showing an increase in surgical site infections at hospitals using laminar airflow (rather than turbulent airflow) in surgery theaters. This is significant because Standard 170 currently recommends laminar airflow in surgery theaters despite the clinical trial evidence to the contrary. Clearly, more clinical trial research is needed in order to recommend ventilation systems for surgery theaters based on facts, not just theories.
The simple approach of moving air from clean to less clean areas is the principle behind the required pressure relationships in Table 7-1 in Standard 170. The table classifies more than 70 types of areas as to whether they should be in a positive or negative pressure relationship with respect to adjacent areas. For some areas there is no requirement—the space maybe positive, negative, or neutral with respect to adjacent areas. For areas where there is a pressure relationship requirement, the return or exhaust air must be ducted.
Compared to earlier regulations, Standard 170 has reduced the requirements for adding humidification to many areas. For clinical reasons, most surgery and critical care areas require a minimum of 20% relative humidity, but all occupied areas are required to maintain humidity levels below 60%, which also helps to reduce concentrations of airborne pathogens.
Standard 170 requires air handling units and air distribution systems to have conveniently located access doors, panels, or other means for access and cleaning. For the most part, compliance with ASHRAE Standard 62.1-2010: Ventilation for Acceptable Indoor Air Quality is sufficient. This applies to the design, installation, start-up, operation, and maintenance of all air handling systems.
The future of HAIs in health care
It is clear that more empirical research is needed regarding the causes of HAI outbreaks. The organisms that cause HAIs are produced in many sources, but the role of the infection control professional should be to defeat the methods by which they are transmitted to patients, caregivers, and visitors.
Until more empirical information is available, the role of the HVAC engineer in infection control should be to use accepted standards to reduce the likelihood that the HVAC systems will promote the growth or transmission of these organisms by using accepted design and construction standards.
Every health care facility is unique. Designers of these facilities must become familiar with all the requirements of Standard 170 and should work closely with the clinical and maintenance staff to ensure that the requirements for providing a safe, reliable, and clean environment are met.
Jim Paul is a vice president with Peter Basso Assocs. He has significant experience in mechanical engineering design and is knowledgeable in the design of complex HVAC, plumbing, and fire protection systems for a variety of project types with a particularly strong emphasis on health care facility design.
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2. The Direct Medical Costs of Health Care-Associated Infections in U.S. Hospitals and the Benefits of Prevention (Scott RD II), Centers for Disease Control and Prevention, March 2009.
3. TABLE 1 – Common Diseases and Organisms in Hospital Environments, (James Paul); Peter Basso Associates, compiled from:
Comparison of operating room ventilation systems in the protection of the surgical site (Memarzadeh F and Manning A), ASHRAE Transactions, V. 108, Pt. 2, 2002.
Effects of Operating Room Geometry and Ventilation System Parameter Variations on the Protection of the Surgical Suite (Memarzadeh F and Jiang Z). IAQ, Critical Operations: Supporting the Healing Environment through IAQ Performance Standards, 2004.
4. Operating Room Ventilation with Laminar Airflow Shows No Protective Effect on the Surgical Site Infection Rate in Orthopedic and Abdominal Surgery (Christan Brandt, MD, Dorit Sohr, PhD, Franz Daschner, MD, PhD, Petra Gastmeier, MD, PhD, and Henning Rüden, MD, PhD), Annals of Surgery, Vol. 248, Number 5, November 2008.
5. ASHRAE Standard 170-2008 Section 7.4.1.
6. New Theories on Plumbing and HVAC Systems (Hermans, Richard, PE, HFDP), ASHE PDC Summit, February 27, 2013.
7. Guidelines for Environmental Infection Control in Health-Care Facilities, Recommendations of CDC and the Health care Infection Control Practices Advisory Committee (HICPAC), U.S. DHHS CDC–2003.
8. Where should one search when confronted with outbreaks of nosocomial infection? (P. Gastmeier, S. Stamm-Balderjahn, S. Hansen, I. Zuschneid, D. Sohr, M. Behnke, R. Vonberg, H. Ruden), American Journal of Infection Control, Volume 34, Issue 9, pages 603-605.