Aerosol and bioaerosol particle size and dynamics from defective sanitary plumbing systems

Gormley, M.; Aspray, T. J.; Kelly, D. A.

Aerosols are readily transported on airstreams through building sanitary plumbing and sewer systems and those containing microbial pathogens (known as bioaerosols) are recognised as contributors to infection spread within buildings. When a defect occurs in the sanitary plumbing system that affects the system integrity, a cross transmission route is created that can enable the emission of bioaerosols from the system into the building. These emission occurrences are characterised as short burst events (typically < 1 minute in duration) which makes them difficult to detect and predict. The characterisation of these emission events is the focus of this research. Two methods were used to characterise bioaerosol emission events in a full scale test rig : (i) an Aerodynamic Particle Sizer (APS) for particle size distribution and concentrations; and (ii) a slit to agar sampler to enumerate the ingress of a viable tracer microorganism (Pseudomonas putida). The APS data confirmed that most particles (> 99.5%) were <5 m and were therefore considered aerosols. Particles generated within the sanitary plumbing system as a result of a toilet flush leads to emissions into the building during system defect conditions with an equivalence of someone talking loudly for over 6 and a half minutes. There were no particles detected of a size > 11 m anywhere in the system. Particle count was influenced by flush volume, but it was not possible to determine if there was any direct influence from airflow rate. Typical emissions resulting from a 6 litre flush were in the range of 200 to 400 particles per second at a concentration of typically 9 to 12 number per cm 3 and a total particle count in the region of 3,000 to 4,000 particles, whereas the peak emissions from a 1.2 litre flush was 60 to 80 particles per second at a concentration of 2.4 to 3 number per cm3 and a total particle count in the region of 886 to 1045 particles. The reduction in particles is in direct proportion to the reduction in flush volume. The slit to agar sampler was able to provide viable time course CFU data and confirmed the origin of the particles to be the tracer microorganism flushed into the system. The time course data also has characteristics consistent with the unsteady nature of a toilet flush.