Tracer study of proximity and recirculation effects on exposure risk in an airliner cabin.

There is continuing concern about whether and to what extent airliner cabins represent an increased risk of transmission of airborne infectious disease. The purpose of this study was to examine through a simple experiment the relative importance of close proximity and partial recirculation of cabin air on the potential risk of disease transmission. Results are presented from measurements of instantaneous point source dispersion in a cabin on a commercial airline flight. A small amount of tracer gas was released as a puff in the passenger cabin of a wide body jet at cruise altitude. Tracer gas samples were taken manually in the period immediately after the release by two technicians sitting 2 m and 30 m forward of the release point in the cabin. The maximum tracer concentration observed at the 2 m sampling point occurred at 5 s after the release and was a factor of 500 greater than the maximum observed at the 30 m sampling point, which occurred 6.5 min after the release. The integrated tracer exposure at the 2 m location was approximately a factor of 30 greater than at the 30 m location. Assuming risk of transmission is proportional to dose, then the results support the hypotheses that infectious diseases are transmitted primarily between people sitting in close proximity to each other in an aircraft cabin and that partial recirculation of ventilation air in the cabin has a negligible impact on occupants' risk of exposure.

A simple method for tracer containment testing of hospital isolation rooms.

A simple method for tracer containment testing of hospital isolation rooms is presented. The method does not require any equipment setup in tested rooms and can be completed in approximately one-half hour per room. Tracer samples are taken at specified time intervals in the corridor outside of an isolation room and analyzed on a portable gas chromatograph system. Results are presented from tracer testing of two isolation rooms in two different hospitals. One isolation room had a significant negative pressure differential between room and corridor, and the other isolation room was not at negative pressure. A small quantity of sulfur hexafluoride gas was injected manually from a polyethylene syringe over a bed in an isolation room. Tracer concentrations were thereafter measured in the corridor adjacent to the room at 5-minute intervals for 20 minutes after the injection, yielding a quantitative measure of leakage of the tracer from the isolation room. Finally, measuring the tracer concentration in the isolation room 30 minutes after injection yielded an indication of how effectively the ventilation system removed a contaminant released at the position of the bed. The results show that an instantaneous release of a small quantity of tracer gas in an isolation room yields tracer concentrations in the corridor outside of the room that are within the analytical range of the measuring equipment both for a properly functioning isolation room and an improperly functioning isolation room, and thus that the method is well-suited for studying containment in hospital isolation rooms. Possible practical applications of the method are discussed.

A tracer method for evaluating recirculation of pollutant releases in buildings.

A method is introduced for evaluating recirculation in a building ventilation system from pollutant emissions in or near the building. Tracer was released at a known rate at the point of pollutant emission. Using measured tracer concentrations, the tracer release rate, and an estimate of the pollutant release rate, pollutant concentrations were estimated at the locations in the building where the tracer was measured. The method can be used to test whether a ventilation system is adequate for maintaining an acceptable work environment before work with a hazardous substance begins. In a case study presented to illustrate the technique, initial attempts to correct a problem of recirculation of sulfuric acid from a fume hood in a chemistry laboratory were shown to be inadequate, prompting the ventilation contractor to make further repairs before work with sulfuric acid could be resumed.