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

Abstract

AbstractAerosols 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 μm 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 > 11μm 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 280 – 400 particles per second at a concentration of typically 9 to 12 number per cm3 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 - 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.