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A multi-zone model evaluation of the efficacy of upper-room air ultraviolet germicidal irradiation.

Authors
Nicas-M; Miller-SL
Source
Appl Occup Environ Hyg 1999 May; 14(5):317-328
NIOSHTIC No.
20024405
Abstract
Engineering controls can be used to reduce the spread of airborne infectious disease, particularly tuberculosis (TB), in high-risk settings. This article evaluates published data on the efficacy of upper-room air ultraviolet germicidal irradiation (UVGI). A three-zone representation of a TB patient room equipped with a germicidal UV lamp is developed. The lamp irradiates the upper-room zone and inactivates airborne mycobacteria; the unirradiated lower-room zone also contains a near-field zone surrounding the TB patient. Infectious particles are generated in the near-field zone and transported throughout the room by air flow between zones. Each zone is independently well-mixed; the whole room, however, is not well-mixed. The three-zone model is applied to a previously published study of UVGI against airborne mycobacteria in a test room. Based on the estimated slopes of the semi-log concentration decay curves for viable mycobacteria, and on the assumption that the test room was essentially well-mixed, the published study reported that UVGI provided 10 to 25 equivalent air changes per hour. However, when the same decay curve slopes are interpreted in the context of the three-zone model, UVGI is seen to be far less effective in reducing exposure intensity near the TB patient. Near-field exposure intensity is relevant because health care workers are usually in close proximity to the TB patients they attend. In general, the interpretation of concentration decay data depends on the specific model of room air mixing that is assumed appropriate. It is recommended that tests of the efficacy of UVGI and other control devices against airborne microorganisms be based on steady-state concentration measurements rather than concentration decay measurements, because the former measurements do not require inferences based on a particular model.
Keywords
Infectious-diseases; Infection-control; Aerosol-particles; Aerosol-sampling; Disease-transmission; Disease-incidence; Disease-control; Risk-analysis; Risk-factors; Health-care-facilities; Health-care-personnel; Simulation-methods; Analytical-models; Germicides; Engineering-controls; Airborne-particles; Ultraviolet-radiation
CODEN
AOEHE9
Publication Date
19990501
Document Type
Journal Article
Funding Amount
161775
Funding Type
Grant
Fiscal Year
1999
NTIS Accession No.
NTIS Price
Identifying No.
Grant-Number-K01-OH-000155
Issue of Publication
5
ISSN
1047-322X
Priority Area
Research Tools and Approaches: Risk Assessment Methods
Source Name
Applied Occupational and Environmental Hygiene
State
CA
Performing Organization
University of California-Berkeley, School of Public Health, Center for Occupational and Environmental Health, Berkeley, CA 94720
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