Guidelines for Environmental Infection Control in Health-Care Facilities (2003) Show
1. Airborne Contaminant RemovalTable B.1. Air changes/hour (ACH) and time required for airborne-contaminant removal by efficiency *The number of air changes per hour and time and efficiency.
* This table is revised from Table S3-1 in reference 4 and has been adapted from the formula for the rate of purging airborne contaminants presented in reference 1435. + Denotes frequently cited ACH for patient-care areas. § Values were derived from the formula: t2 – t1 = – [ln (C2 / C1) / (Q / V)] X 60, with t1 = 0 where t1 = initial timepoint in minutes ¶ Values apply to an empty room with no aerosol-generating source. With a person present and generating aerosol, this table would not apply. Other equations are available that include a constant generating source. However, certain diseases (e.g., infectious tuberculosis) are not likely to be aerosolized at a constant rate. The times given assume perfect mixing of the air within the space (i.e., mixing factor = 1). However, perfect mixing usually does not occur. Removal times will be longer in rooms or areas with imperfect mixing or air stagnation.213 Caution should be exercised in using this table in such situations. For booths or other local ventilation enclosures, manufacturers’ instructions should be consulted. Top of Page 2. Air Sampling for Aerosols Containing LegionellaeAir sampling is an insensitive means of detecting Legionella pneumophila, and is of limited practical value in environmental sampling for this pathogen. In certain instances, however, it can be used to
Top of Page Methods used to sample air for legionellae include impingement in liquid, impaction on solid medium, and sedimentation using settle plates.1436 The Chemical Corps.-type all-glass impingers (AGI) with the stem 30 mm from the bottom of the flask have been used successfully to sample for legionellae.1436 Because of the velocity at which air samples are collected, clumps tend to become fragmented, leading to a more accurate count of bacteria present in the air. The disadvantages of this method are
Yeast extract broth (0.25%) is the recommended liquid medium for AGI sampling of legionellae;1437 standard methods for water samples can be used to culture these samples. Andersen samplers are viable particle samplers in which particles pass through jet orifices of decreasing size in cascade fashion until they impact on an agar surface.1218 The agar plates are then removed and incubated. The stage distribution of the legionellae should indicate the extent to which the bacteria would have penetrated the respiratory system. The advantages of this sampling method are
Top of Page 3. Calculation of Air Sampling ResultsAssuming that each colony on the agar plate is the growth from a single bacteria-carrying particle, the contamination of the air being sampled is determined from the number of colonies counted. The airborne microorganisms may be reported in terms of the number per cubic foot of air sampled. The following formulas can be applied to convert colony counts to organisms per cubic foot of air sampled.1218 For solid agar impactor samplers: C / (R H P) = N where N = number of organisms collected per cubic foot of air sampled For liquid impingers: (C H V) / (Q H P H R) = N where C = total number of colonies from all aliquots plated Top of Page 4. Ventilation Specifications for Health-Care FacilitiesThe following tables from the AIA Guidelines for Design and Construction of Hospitals and Health-Care Facilities, 2001 are reprinted with permission of the American Institute of Architects and the publisher (The Facilities Guidelines Institute).120 Note: This table is Table 7.2 in the AIA guidelines, 2001 edition. Superscripts used in this table refer to notes following the table. Table B.2. Ventilation requirements for areas affecting patient care in hospitals and outpatient facilities1The format of this section was changed to improve readability and accessibility. The content is unchanged.Surgery and critical careVentilation requirements for surgery and critical care areas.
Top of Page NursingVentilation requirements for nursing areas.
Top of Page Ancillary/Radiology19Ventilation requirements for radiology areas.
Top of Page LaboratoryVentilation requirements for laboratory areas.
Top of Page Diagnostic and treatmentVentilation requirements for diagnostic and treatment areas.
Top of Page Sterilizing and supplyVentilation requirements for sterilizing and supply areas.
Top of Page Central medical and surgical supplyVentilation requirements for central medical and surgical supply areas.
Top of Page ServiceVentilation requirements for service areas.
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Top of Page Appendix I: A7. Recirculating devices with HEPA filters may have potential uses in existing facilities as interim, supplemental environmental controls to meet requirements for the control of airborne infectious agents. Limitations in design must be recognized. The design of either portable or fixed systems should prevent stagnation and short circuiting of airflow. The supply and exhaust locations should direct clean air to areas where health-care workers are likely to work, across the infectious source, and then to the exhaust, so that the healthcare worker is not in position between the infectious source and the exhaust location. The design of such systems should also allow for easy access for scheduled preventative maintenance and cleaning. A11. The verification of airflow direction can include a simple visual method such as smoke trail, ball-in-tube, or flutterstrip. These devices will require a minimum differential air pressure to indicate airflow direction. Top of Page Note: This table is Table 8.1 in the AIA guidelines, 2001 edition. Superscripts used in this table refer to notes following the table. Table B.3. Pressure relationships and ventilation of certain areas of nursing facilities1Pressure relationships and ventilation of certain areas.
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Top of Page Table B.4. Filter efficiencies for central ventilation and air conditioning systems in general hospitals*Filter efficiencies for central ventilation, listing number of filter beds and efficiency (%) of each for hospitals.
Note: This table is Table 7.3 in the AIA guidelines, 2001 edition. * Additional roughing or prefilters should be considered to reduce maintenance required for filters with efficiency higher than 75%. The filtration efficiency ratings are based on average dust sopt efficiency per ASHRAE 52.1–1992. Top of Page Table B.5. Filter efficiencies for central ventilation and air conditioning systems in outpatient facilities*Filter efficiencies for central ventilation in outpatient facilities.
Note: This table is Table 9.1 in the AIA guidelines, 2001 edition. * Additional roughing or prefilters should be considered to reduce maintenance required for main filters. The filtration efficiency ratings are based on dust spot efficiency per ASHRAE 52.1–1992. + These requirements do not apply to small primary (e.g., neighborhood) outpatient facilities or outpatient facilities that do not perform invasive applications or procedures. Top of Page Table B.6. Filter efficiencies for central ventilation and air conditioning systems in nursing facilitiesFilter efficiencies for central ventilation, in nursing facilities.
Note: This table is Table 8.2 in the AIA guidelines, 2001 edition. * The filtration efficiency ratings are based on average dust spot efficiency as per ASHRAE 52.1–1992. Top of Page Table B.7. Filter efficiencies for central ventilation and air conditioning systems in psychiatric hospitalsFilter efficiencies for central ventilation in psychiatric hospitals.
Note: This table is Table 11.1 in the AIA guidelines, 2001 edition. * The filtration efficiency ratings are based on average dust spot efficiency as per ASHRAE 52.1–1992. Top of Page |