Chun-Wan Chen

Effects of ultraviolet germicidal irradiation and swirling motion on airborne Staphylococcus aureus, Pseudomonas aeruginosa and Legionella pneumophila under various relative humidities.

UNLABELLED Staphylococcus aureus, Pseudomonas aeruginosa, and Legionella pneumophila have been detected in indoor air and linked to human infection. It is essential to adopt control methods to inactivate airborne pathogens. By passing bioaerosols horizontally into a UV device at two flow rates (Qs) and moving cells around a central UVC lamp at relative humidity (RH) of 12.7-16.7%, 58.7-59.6%, and 87.3-90%, the effects of swirling motion and 254-nm ultraviolet germicidal irradiation (UVGI) against bioaerosols were assessed under UV-off and UV-on settings, respectively. An inverse relationship between RH and UVGI effectiveness was observed for every test bioaerosol (r = -0.74 ∼ -0.81, P < 0.0001). Increased UV resistance with RH is likely associated with the hygroscopicity of bioaerosols, evident by increased aerodynamic diameters at high RH (P < 0.05). UVGI effectiveness was significantly increased with decreasing Q (P < 0.0001). Moreover, P. aeruginosa was the most susceptible to UVGI, while the greatest UV resistance occurred in L. pneumophila at low RH and S. aureus at medium and high RH (P < 0.05). Results of UV off show P. aeruginosa and L. pneumophila were more sensitive to air-swirling motion than S. aureus (P < 0.05). Overall, test bioaerosols were reduced by 1.7-4.9 and 0.2-1.7 log units because of the UVGI and swirling movement, respectively. PRACTICAL IMPLICATIONS The studied UV device, with a combination of swirling motion and UVGI, is effective to inactivate airborne S. aureus, P. aeruginosa, and L. pneumophila. This study also explores the factors governing the UVGI and swirling motion against infectious bioaerosols. With understanding the environmental and operational parameters, the studied UV device has the potential to be installed indoors where people are simultaneously present, for example, hospital wards and nursing homes, to prevent the humans from acquiring infectious diseases.

Filter Quality of Pleated Filter Cartridges

The performance of dust cartridge filters commonly used in dust masks and in room ventilation depends both on the collection efficiency of the filter material and the pressure drop across the filter. Currently, the optimization of filter design is based only on minimizing the pressure drop at a set velocity chosen by the manufacturer. The collection efficiency, an equally important factor, is rarely considered in the optimization process. In this work, a filter quality factor, which combines the collection efficiency and the pressure drop, is used as the optimization criterion for filter evaluation. Most respirator manufacturers pleat the filter to various extents to increase the filtration area in the limit space within the dust cartridge. Six sizes of filter holders were fabricated to hold just one pleat of filter, simulating six different pleat counts, ranging from 0.5 to 3.33 pleats cm(-1). The possible electrostatic charges on the filter were removed by dipping in isopropyl alcohol, and the air velocity is fixed at 100 cm s(-1). Liquid dicotylphthalate particles generated by a constant output atomizer were used as challenge aerosols to minimize particle loading effects. A scanning mobility particle sizer was used to measure the challenge aerosol number concentrations and size distributions upstream and downstream of the pleated filter. The pressure drop across the filter was monitored by using a calibrated pressure transducer. The results showed that the performance of pleated filters depend not only on the size of the particle but also on the pleat count of the pleated filter. Based on filter quality factor, the optimal pleat count (OPC) is always higher than that based on pressure drop by about 0.3-0.5 pleats cm(-1). For example, the OPC is 2.15 pleats cm(-1) from the standpoint of pressure drop, but for the highest filter quality factor, the pleated filter needed to have a pleat count of 2.65 pleats cm(-1) at particle diameter of 122 nm. From the aspect of filter quality factor, this study suggests that the respirator manufacturers should add approximately 0.5 pleats cm(-1) to the OPC derived from the generalized correlation curve for pleated filter design based on minimum pressure drop.

Particle Size Concentration Distribution and Influences on Exhaled Breath Particles in Mechanically Ventilated Patients

Humans produce exhaled breath particles (EBPs) during various breath activities, such as normal breathing, coughing, talking, and sneezing. Airborne transmission risk exists when EBPs have attached pathogens. Until recently, few investigations had evaluated the size and concentration distributions of EBPs from mechanically ventilated patients with different ventilation mode settings. This study thus broke new ground by not only evaluating the size concentration distributions of EBPs in mechanically ventilated patients, but also investigating the relationship between EBP level and positive expiratory end airway pressure (PEEP), tidal volume, and pneumonia. This investigation recruited mechanically ventilated patients, with and without pneumonia, aged 20 years old and above, from the respiratory intensive care unit of a medical center. Concentration distributions of EBPs from mechanically ventilated patients were analyzed with an optical particle analyzer. This study finds that EBP concentrations from mechanically ventilated patients during normal breathing were in the range 0.47–2,554.04 particles/breath (0.001–4.644 particles/mL). EBP concentrations did not differ significantly between the volume control and pressure control modes of the ventilation settings in the mechanically ventilated patients. The patient EBPs were sized below 5 µm, and 80% of them ranged from 0.3 to 1.0 µm. The EBPs concentrations in patients with high PEEP (> 5 cmH2O) clearly exceeded those in patients with low PEEP (≤ 5 cmH2O). Additionally, a significant negative association existed between pneumonia duration and EBPs concentration. However, tidal volume was not related to EBPs concentration.

496 Shift of aerosol penetration in size-selective cyclone samplers

Introduction Size-selective aerosol samplers are used to assess the health effect, because the retention of deposited particles in the respiratory tract is strongly size dependent. The main objective of this work is to examine the particle loading effects on PM2.5 cyclone samplers. Methods In this work, five PM2.5 cyclones of different body diameters (9.3–35.6 mm), derived from the BGI VSCC, were designed and fabricated to investigate the effects of particle loading. An ultrasonic atomizing nozzle was used to generate micro-meter-sized potassium sodium tartrate (PST) particles and Sodium chloride (NaCl) particles as solid challenge aerosols, and di-ethyl-hexyl-sebacate (DEHS) particles as liquid challenge particles. Aerosol number size distributions and concentrations, both upstream and downstream of the cyclones, were measured using an aerodynamic particle sizer. In addition to the cyclone body diameter, other parameters investigated in this work included: challenge aerosol size distribution, chamber humidity, and the material of the cyclone. Results The PM2.5 cyclones could be used to sample liquid particles without any bias, because the deposited liquid aerosols dripped down and did not accumulate on the inner wall of the cyclone. However, when challenged with solid particles, the deposited and accumulated aerosols on the wall reduced the aerosol penetration, and changed the curve to be less sharp. The extent of underestimation was affected by many parameters, such as challenge aerosol size distribution, humidity, test agent, and the elastic properties of the cyclone and the test agent. On average, there was an underestimation of 20% of 2.5 µm aerosol penetration when challenged with PST particles, regardless of cyclone body size. This suggested that cyclones might not be ideal for sampling solid particles. Discussion Cyclone samplers currently used for size-selective sampling are likely subject to aerosol loading effect, and resulted in underestimation of the PM2.5 measurements. The use of virtual cyclone or wet cyclone might solve parts of the problem.

176 Modification and improvement of fit test method using ambient aerosols

Introduction Fit testing should be performed before the use of tight-fitting respirators. However, it may not always be conducted for various reasons, mostly time consuming and costly. This study aimed to shorten the fit testing procedures by improving the instrumental settings, sampling system design, and data analysis protocols. Methods Experiments of fit factor measurements were divided into two parts: constant flow and cyclic flow using a breathing simulator. To simulate leakage, capillaries (10 mm in length, diameter 1.0–1.5 mm) were used to insert on N95 and N100 filtering facepieces. The ratio of total to leak flow was considered the ‘true fit factor, FFt’. Flow rates ranging from 5–50 L/min were employed to study the flow dependency. The measured fit factors were determined by concurrent particle concentration measured by a Portacount and a OPS 3330. The default 1.7 m sampling tube was used to connect filtering facepiece to the aerosol instruments. In addition, the effects of breathing pattern (tidal volume: 0.5–1 L, frequency: 5–20 times/min) and lung deposition (with/without HEPA filter behind the respirator) on in-mask particle concentration during fit testing were analysed, to explore the minimal sampling time that approximated the FFt. Results The particle measurement response times for Portacount and OPS were approximately 5 and 2 s, respectively. For P100 respirators, most measured fit factors were close to the FFt. Whereas, there was an underestimation while using N95 respirator due to filter penetration. Therefore, N95-companion was necessary while testing N95 respirator. For the cyclic flow tests, the fit factor was overestimated because the sampling tube was connected onto the facepiece where filtered air was partly sampled. The higher the breathing flow rate, the more the fit factor was overestimated. On the other hand, the measured fit factor would be close to the FFt when using the highest concentration during a breathing cycle (FFmin). In theory, it could be decided in only one breathing cycle. Conclusion With improved design in instrumental setting and operating procedures, a fit test for an individual exercise would take approximately only 12 s. Therefore, the whole fit testing process could be shortened from 7.5 to about 3 min.