Abstract

Detrimental impacts associated with inhalation of ultrafine particles (UFPs) (diameter of particle, Dp <100 nm), on various respiratory organs, can be controlled by means of N95 filtering facepiece respirators (FFRs), widely used by industrial and healthcare workers. In this regard, investigation of N95 FFRs efficiency, against UFPs, under cyclic flow, in addition with constant flow, is very necessary, since cyclic flow represents actual breathing pattern.

The first objective of the thesis was to report the development of a procedure to investigate the individual impact of breathing frequency and flow rate on the performance of N95 FFRs. Experiments were performed for two peak inhalation flows (PIFs) (135 and 360 L/min) and two breathing frequencies (24 and 42 breaths per minute (BPM)) for a total of four cyclic flows. The results showed that, for the most penetrating particle size (MPPS) range, an increase in both PIF and breathing frequency could potentially enhance the penetration; however the effect of PIF was observed to be much more pronounced than frequency. Therefore, from low to high respiratory efforts, a huge portion of penetration enhancement was due to the PIF variations and only a small portion was contributed by the frequency variations.

With the second objective of the thesis, the penetrations measured with the cyclic flows (with mean inhalation flows (MIFs) ranging from 42 to 360 L/min) were compared with those measured with the constant flows equal to the cyclic flow minute volume, mean inhalation flow (MIF) and peak inhalation flow (PIF). The results indicated that, for the MPPS, constant flows equal to the cyclic flow minute volume and PIF significantly underestimated and overestimated the penetration of cyclic flows, respectively. Constant flows equal to the MIFs of cyclic flows, however, resulted in closer penetrations compared to the cyclic flows. At higher flow rates, of course, the maximum penetrations under constant flow exceeded the maximum penetrations under cyclic flow (MIF).

With the third objective of the thesis, the impact of particle loading on the penetration was tested. Investigations were performed with a cyclic flow (with equivalent MIF of 170 L/min) and two constant flow rates (85 L/min and 170 L/min) for a period of 6-hour loading time. The results indicated that, for small particles (usually less than 100 nm), the particle loading effect lead to decrease in the penetration with the loading time. The MPPS was also found to shift towards larger sizes, as the respirators were loaded with more particles. For the final stage of loading, unlike the initial stage, the penetration of a large range of particles under cyclic flow was significantly higher than the penetrations under constant flow (equal to cyclic flow MIF).