AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Some Aspects of Aerosol Production by Modern Flush Toilets of Various Designs
DAVID L. JOHNSON, Robert A. Lynch, Jacob F. Jones, Kenneth R. Mead, Deborah V.L. Hirst, Dept Occup/Envir Health, Univ OK HSC
Abstract Number: 26 Working Group: Health Related Aerosols
Abstract Background. A microbe-contaminated toilet will produce bioaerosol droplets when flushed, some of which will remain airborne. We assessed toilet plume aerosol from dual flush high efficiency (HET), dual flush pressure-assisted high efficiency (PAT), and Flushometer siphonic toilets.
Methods. Both total and droplet nuclei “bioaerosol” production were assessed for the toilets, which had similar bowl water and flush volumes. Monodisperse 0.25 or 0.30 µm fluorescent microspheres served as microbe surrogates. Experiments were conducted in the particle-free environment of a mockup 175 cu ft water closet (WC) purged with HEPA-filtered air. Bowl water was seeded with microspheres before each flush. Airborne particles were sampled onto 0.2µm pore size MCE filters for 30 minutes beginning 15 minutes after the flush, using 4 open-face cassettes mounted 2 and 5 feet high on the WC side walls. Pre- and post-flush bowl water samples were filtered through the same type filter, and all filter particle counts were analyzed via fluorescent microscopy.
Results. Bowl headspace droplet count size distributions were bimodal and similar for all toilet types and flush conditions, with 95% of droplets < 2 µm diameter and over 99% < 5 µm. Up to 145,000 droplets were produced per flush, with the relatively high energy Flushometer producing over 3 times as many as the lower energy PAT and over 12 times as many as the lowest energy HET despite similar flush volumes. However, the mean numbers of fluorescent particles aerosolized and remaining airborne were similar for the three toilets at approximately 1100-1200 per flush.
Conclusions. Toilets produced denser aerosols, but with similar size distributions, with increasing flush energy. However, the number of droplet nuclei “bioaerosols” was similar for similar flush volumes. These findings suggest two concurrent aerosolization mechanisms – splashing for large droplets and bubble bursting for the fine droplets that form droplet nuclei.