Engineering Controls Database
Expedient Airborne Infection Isolation
| NIOSH has conducted research on airborne infection isolation based on a well-documented acknowledgment of insufficient engineered airborne infection isolation capacity within the United States healthcare system. This coincided with an increased awareness of the threat demonstrated by terrorism concerns, recent experiences with severe acute respiratory syndrome (SARS), the ongoing evolution of influenza virus strains, and documented respirator shortages that could occur during a moderately-prolonged airborne infectious epidemic. | |
| During a mass casualty or pandemic event, it is possible that isolation needs will surpass available isolation units. Without expedient, cost-effective options for airborne isolation, the alternatives will be an abandonment of many airborne infection isolation (AII) practices, patients cohorting within large “hot zones” of potential airborne infectious aerosol, and healthcare workers relying on N95 respirators or even surgical masks for protection. | |
The purpose of this research was to evaluate portable filtration technology combined with increased levels of containment (as opposed to general room dilution) and directed airflows to provide expedient airborne isolation capability to a variety of healthcare settings not currently equipped for such isolation. The selection of this technology was driven by its compatibility with existing ventilation systems, its affordability, and its recognition in published literature as an available engineering control to assist in patient isolation [Marier and Nelson 1993]. Two approaches were studied, zone-within-zone dilution filtration (figure 1) and local exhaust ventilation (LEV) via ventilated headboard (figure 2).  Zone-within-Zone dilution filtration In ventilation system design, a “zone” is the space served by a ventilation system. The zone-within-zone isolation approach involved establishing a high-ventilation-rate inner isolation zone within a larger ventilated zone, by enclosing and ventilating the space immediately around an infectious patient’s bed within a ventilated room. The approach relied upon a high dilution ventilation rate within the smaller contained inner isolation zone to rapidly dilute airborne contaminant levels within that space. This smaller inner zone was defined using a floor-to-ceiling retractable curtain with a designated curtain gap as the entrance point. The inner zone was located within a larger outer zone, which was defined by the overall patient room boundary. Air was exhausted from the inner zone through the use of a freestanding HEPA filtration system that utilized a nonducted air inlet. The HEPA system was positioned to serve two patient inner-zones simultaneously, with no exchange of contaminated air between the inner zones. LEV via ventilated headboard The ventilated headboard expedient isolation approach relied upon an LEV configuration to create localized capture of patient-generated contaminant before the contaminant had an opportunity to dilute throughout the overall patient room. A semi-enclosing hood (retractable when required for extensive hands-on patient care) extended over and along both sides of the pillow area of the patient bed and assisted in establishing parallel flow streamlines across the contaminant generation point (the patient’s head) and into the ventilated headboard, without requiring excessive capture velocities to overcome potential room cross-currents. The ventilated headboard was ducted to a small, portable HEPA filtration unit, similar to those used to contain dust and other aerosol contaminants during construction renovation activities in healthcare facilities. |
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DART/EPHB [2012]. Expedient methods for surge airborne isolation within healthcare settings during response to a natural or manmade epidemic. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Pre¬vention, National Institute for Occupational Safety and Health, Division of Applied Research and Technology (DART), Engineering and Physical Hazards Branch (EPHB), EPHB Publication No. EPHB 301-05f. Marier RL, Nelson T [1993]. A ventilation-filtration unit for respiratory isolation [see comment]. Infect Control Hosp Epidemiol 14(12):700–705. Mead, Kenneth and David L. Johnson (2004). An Evaluation of Portable HEPA Filtration for Expedient Patient Isolation in Epidemic and Emergency Response. Annals of Emergency Medicine 44(6):635-645. |
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engineering controls engineering controls expedient airborne isolation expedient airborne isolation healthcare workers healthcare workers infectious agents infectious agents |
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| The evaluated expedient airborne isolation configurations were universally successful in their ability to contain surrogate infectious aerosol within the inner isolation zones. Center-of-room sample results across all sites and configurations resulted in geometric mean reduction ratios (GMRRs) ranging from 99.5 to 99.9 percent with 90 percent lower confidence limits ranging from 97 to 99.6 percent. Worker exposure reductions were more variable depending upon room configuration corner-to-corner/zone-within-zone isolation configurations under the evaluated test conditions; however, these areas still benefited from the increased dilution at a set ventilation rate that resulted from establishing the smaller isolation zone. For the two side-draft/zone-within-zone configurations and all of the ventilated headboard field studies, GMRR results observed for healthcare worker positions ranged from 98.7 to 99.9 percent, with lower 90 percent limits ranging from 94.7 to 99.6 percent. Analysis of temperature log data revealed either no impact or insignificant impact in regards to moving room temperatures outside of the ASHRAE-recommended range of 70–75°F. |