Abstract
Negative-pressure isolation rooms (NPIRs) are used to isolate patients who have a suspected or known airborne infectious disease from the general hospital environment. When a person passes through an NPIR doorway, there exists an exchange of air between the isolation room and the area beyond its door. In a recent study, National Institute for Occupational Safety and Health researchers used sulfur hexafluoride tracer gas to examine the magnitude of air volume migration (AVM) as a function of several independent variables. A small cart carried a mannequin through a doorway separating a laboratory NPIR and a sulfur hexafluoride measurement chamber. The configuration provided simulated entry/exit of a healthcare worker through the doorway. Upon completion of experiments using a swinging door (including various cycle speeds for the door), a sliding door was installed and the experiments were repeated. In all cases examined, air flow rate differential between the air supplied to, and exhausted from, the NPIR was the only statistically significant factor in determining the level of AVM. Across the range of flow differentials examined (50 to 220 ft3/min), AVM ranged from 35 to 65 ft3. This range of AVM remained statistically unchanged regardless of door type, operating speed of the door, or entry to or exit from the NPIR. (Although entry/exit did significantly increase AVM, travel direction, whether entering or exiting the NPIR, did not.) By knowing the level of AVM during entry/exit through a doorway - a cause of airborne contaminant migration through a facility - a more complete assessment of the risk of transmission of an airborne infectious disease is made possible. This study shows that an anteroom or buffer zone outside the contaminated area's doorway will offer a degree of containment during entry/exit not otherwise obtainable. While this study concerned itself primarily with the engineering control of the transmission of airborne infectious diseases provided by ventilation systems, the results are applicable to any environment where a clean area is separated from a less clean area by a doorway.
