SARS and Air Filtration Application
Severe Acute Respiratory Syndrome (SARS) is thought to be spread through airborne droplets generated from coughing, sneezing or talking. It is also possible to contract the virus from contact with body secretions that typically emanate from the eyes, nose or mouth. Droplet infection is most likely within 3 feet of infected patients. It is also important to note that unlike most viruses which cannot live outside a host for long periods, SARS has been noted to survive up to 24 hours on uncleaned surfaces. Current standard infection control practices are being recommended for environmental areas where suspected SARS patients, or probable infected individuals, are being cared for.
The environment should be controlled by using proven methods to reduce the probability of exposure. Possible control methods include individual respiratory protection, direct source capture using local exhaust ventilation, controlling air flow direction to prevent cross-contamination, dilution and removal of contaminated air through general ventilation, and air cleaning through air filtration and ultraviolet germicidal irradiation.
The information presented includes recommendations from the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) and the United States Department of Health & Human Services (DHHS). It is important to note that while some of these guidelines are also expressed in the Centers for Disease Control document, Guidelines for the Control of Mycobacterium Tuberculosis (TB), TB is a bacterium whose size is measured in microns. The coronavirus associated with SARS is viral and measured in nucleotides (magnitudes smaller than a micron).
These recommendations are consistent with current World Health Organization (WHO) and CDC recommended precautions for environmental control for SARS.
Critical areas for environmental control include waiting/admittance areas, treatment areas, patient rooms, satellite treatment areas and defined infectious isolation rooms. The following chart shows recommendations for specific areas of a medical facility.
It is important to note that negative pressure can only be maintained when access is controlled (door closed). Doors should only be opened for entrance and exiting of attending personnel, and should be closed immediately afterwards.
When exhausting air from an isolation room, exhaust criteria should be used as defined by the ASHRAE Fundamentals Handbook Chapter 14 or the ACGIH Industrial Ventilation Manual (never less than within 30 feet of inhabitant areas). Air should not be exhausted in the vicinity of walkways or adjacent to windows or openings that may allow re-entrance of contaminant.
When infectious isolation rooms cannot be 100% exhausted, HEPA filters should be used in duct systems discharging into general ventilation (recirculated air), in ducts for individual room recirculation, in exhaust ducts from booths and enclosures, or in exhaust ducts to remove droplet nuclei from being discharged to other facility areas of habitation.
It is important to note that a HEPA filter is tested and certified to meet HEPA performance criteria (procedure as defined by the Institute of Environmental Sciences & Technology (IEST)). The term HEPA has been misused in the air filtration industry. For critical applications as defined herein, you should request a letter of certification with each filter. This is common practice in the air filtration industry when critical applications are involved. These documents are supplied free of charge if they are requested at the same time the filter is ordered. For your facility’s protection, these letters should be stored in a file to note conformity with the latest standards of care or recommended practices.
Air filtration serves an important function in the control of airborne droplet nuclei. A MERV 14 filter, as evaluated by ASHRAE Filter Testing Standard 52.2, will be more than 95% efficient in removing droplet nuclei provided it is given the opportunity to clean the air by moving air through the filter.
In critical situations, air changes should be increased to the maximum ability of the HVAC system serving the area. Variable air volume systems should be modified to operate at full capacity, and the fan on all systems should be in the constant-on position rather than the typical mode of cycling based upon temperature. Please note that if an air filter can remove 90% of all 1 micron size particles within a space in 23 minutes, the same filter only requires 9 minutes if the air change rate is increased to 15.
Exposure and susceptibility towards contracting a disease are linked to the volume of contaminant that the individual is exposed to. If the volume of contaminant is reduced, the individual’s risk of contraction is also reduced. Air filters and air changes are the critical factors in this equation.
Camfil Farr can provide a copy of the CDC Guidelines for the Control of Mycobacterium Tuberculosis (the document most often referred to in infectious disease situations) and some of the latest published materials specific to SARS. All documents are in PDF format and compressed into one zip file. Send your name, affiliation and e-mail to: literature@camfilfarr.com for your electronic copy. Click here to send request.
Your local Camfil Farr Distributor is well versed in the intricacies of applying air filtration in medical or other critical care facilities. Your local Camfil Farr Representative can assist engineering and contracting firms in new system or room design. Contact camfilfarr@camfilfarr.com for the name of your local Camfil Farr agency.
Additional important SARS sites:
Hospital Infection Control Guidance for Severe Acute Respiratory Syndrome (SARS), World Health Organization,
http://www.who.int/csr/sars/infectioncontrol/en/
SARS, What Everyone Should Know,
United States Centers for Disease Control,
http://www.cdc.gov/ncidod/sars/index.htm