Measuring the flushing-generated flow and aerosols in lavatory of commercial aircraft

Lavatory use on commercial aircraft may present a risk of contagion, especially on long-haul flights. Flushing the toilet can induce a strong sweeping flow, which generates aerosols in the toilet bowl and also resuspends deposited particles from lavatory surfaces. Currently, the generation of aerosols, the flushing-induced airflow, and the potential of airborne particle exposure for a lavatory user are unclear. This investigation performed in-flight tests to measure the particle concentrations in the toilet bowl, near the floor, and in the breathing zone. A lavatory mockup was constructed in a laboratory for visualization of the airflow and measurement of airflow speeds. After the similarity in particle generation between the in-flight test and mockup model had been verified, the residual ratio of the generated aerosols in the toilet bowl after flushing was determined. Then the total number of generated aerosols in the toilet bowl of a commercial aircraft was inferred. In addition, the effects of the drainage pressure and rinse water pressure on the particle concentrations and spectrum were measured and evaluated. The results revealed that the total number of aerosols larger than 0.3 μm generated by the flushing of a toilet on a typical aircraft was 8498 ± 1,918, of which the submicron particles comprised 92%. A higher drainage pressure or a lower rinse water pressure resulted in a lower monitored aerosol concentration. The concentration in the breathing zone with an open toilet lid was clearly higher than that with a closed toilet lid, which should be given careful attention.