Ali Bahloul

Impact of two particle measurement techniques on the determination of N95 class respirator filtration performance against ultrafine particles.

The purpose of this experimental study was to compare two different particle measurement devices; an Electrical Low Pressure Impactor (ELPI) and a Scanning Mobility Particle Sizer (SMPS), to measure the number concentration and the size distribution of NaCl salt aerosols to determine the collection efficiency of filtering respirators against poly disperse aerosols. Tests were performed on NIOSH approved N95 filtering face-piece respirators (FFR), sealed on a manikin head. Ultrafine particles found in the aerosols were also collected and observed by transmission electron microscopy (TEM). According to the results, there is a systematic difference for the particle size distribution measured by the SMPS and the ELPI. It is largely attributed to the difference in the measurement techniques. However, in spite of these discrepancies, reasonably similar trends were found for the number concentration with both measuring instruments. The particle penetration, calculated based on mobility and aerodynamic diameters, never exceeded 5% for any size range measured at constant flow rate of 85 L/min. Also, the most penetrating particle size (MPPS), with the lowest filtration efficiency, would occur at a similar ultrafine size range <100 nm. With the ELPI, the MPPS was at 70 nm aerodynamic diameter, whereas it occurred at 40 nm mobility diameter with the SMPS.

The Need for a Comprehensive Approach to Managing Confined Space Entry: Summary of the Literature and Recommendations for Next Steps

Despite all the regulatory and standard-setting efforts that have been made in North America, judging from the most recent statistics many fatal incidents related to work in confined spaces still occur. In Canada, fatal incidents in the province of Quebec reveal failures in and absence of the identification and preparation of work situations in confined spaces and in risk management. In this study, we performed a literature review consisting of 77 documents on existing hazards and risk assessment for confined spaces. Moreover, we formulated proposals regarding the design of specific and improved tools for assessing such risks. We found that atmospheric hazards monopolized attention in the literature on confined spaces, while risk estimation specific to confined space interventions received little practical coverage overall, apart from atmospheric hazards. The parameters used to establish classes or groupings of confined spaces in existing tools were imprecise. The development of a risk analysis process that is (i) more systematic and based on the concepts recognized in risk management standards, (ii) multidisciplinary, and (iii) adapted to the specific characteristics of confined spaces is therefore needed. Such a process will better support managers and occupational health and safety (OH&S) personnel in their efforts to prioritize and reduce risks. Suggestions on such a risk analysis tool and categorization of interventions in confined spaces are proposed in this article. Lastly, risk analysis tools adapted to confined space interventions are needed to ensure the inherently safe design of these spaces.

Contribution of Breathing Frequency and Inhalation Flow Rate on Performance of N95 Filtering Facepiece Respirators

The investigation of particle penetration through filtering facepiece respirators under cyclic flows is very necessary because cyclic flows represent actual breathing flow patterns. This article reports the development of a procedure to investigate the individual impact of breathing frequency and flow rate on the performance of N95 filtering facepiece respirators. Experiments were performed for two peak inhalation flows (PIFs; 135 and 360 l min(-1)) and two breathing frequencies [24 and 42 breaths per minute (BPM)] for a total of four cyclic flows (Flow A: 135 l min(-1) and 24 BPM; Flow B: 135 l min(-1) and 42 BPM; Flow C: 360 l min(-1) and 24 BPM; and Flow D: 360 l min(-1) and 42 BPM). Each experiment was performed using two different set-ups: the first set-up included both inhalations and exhalations through the filter media and test chamber, while with the second set-up, only inhalation flows were considered. The results showed that, for the most penetrating particle size range, an increase in both PIF and breathing frequency could potentially enhance the penetration with both set-ups; however, the effect of PIF was observed to be much more pronounced than that of frequency. The results indicated that with both set-ups, when the PIF was increased from 135 to 360 l min(-1) (for the given frequency: 24 or 42 BPM), an increase of up to 139-152% in penetration was observed. On the other hand, only a 10-16% increase in penetration occurred when the frequency was changed from 24 to 42 BPM (for a given PIF: 135 or 360 l min(-1)). This suggests that, from low to high respiratory efforts, a huge portion of penetration enhancement is due to PIF variations and only a small portion is contributed by frequency variations.

Evaluation of N95 Filtering Facepiece Respirator Efficiency with Cyclic and Constant Flows

An increasing demand for protecting workers against harmful inhalable ultrafine particles (UFPs), by means of filtering facepiece respirators (FFRs), necessitates assessing the efficiency of FFRs. This article evaluates the penetration of particles, mostly in the ultrafine range, through one model of N95 FFRs exposed to cyclic and constant flows, simulating breathing for moderate to heavy work loads. The generated particles were poly-dispersed NaCl, within the range of 10–205.4 nm. The tests were performed for several cyclic flows, with mean inhalation flows (MIFs) ranging from 42 to 360 L/min, and constant flows with the same range. The measurements were based on filter penetration and did not consider particle leakage. With the penetrations recorded for the selected constant and cyclic flows, the worst-case scenario penetrations at the most penetrating particle size (MPPS) were obtained. The MPPS penetrations measured with the cyclic and constant flows equivalent to minute volume, MIF and peak inhalation flow (PIF) of the cyclic flows were then compared. It was indicated that the constant flows equivalent to the minute volume or PIF of the cyclic flow could not accurately represent the penetration of the corresponding cyclic flow: the constant flow equal to the minute volume of the cyclic flow significantly underestimated the MPPS penetration of the corresponding cyclic flow, while the constant flow equal to the PIF of the cyclic flow overestimated it. On the other hand, for the constant flow equal to the MIF of the cyclic flow, the MPPS penetrations were almost equal for both the constant and cyclic flows, for the lower flow rates (42 to 170 L/min). For higher flow rates (230 to 360 L/min), however, the MPPS penetration was exceeded under the constant flows, compared with the corresponding cyclic flows. It was therefore concluded that the constant flow equal to the MIF of the cyclic flow could better predict the results of corresponding cyclic flow, since it could provide the MPPS penetrations (worst-case scenario) equal to or greater than the MPPS penetrations of the cyclic flow.

Deactivation and ultraviolet C-induced regeneration of photocatalytic oxidation air filters

Ultra-violet photocatalytic oxidation has been regarded as one of the promising air purification technologies for improving indoor air quality. However, limited availability of experimental data in terms of photocatalyst deactivation and regeneration has hindered successful implementation of ultra-violet photocatalytic oxidation air cleaners in mechanical ventilation systems. The objective of this study is to obtain knowledge of the ultraviolet C-induced regeneration method, the simplest on-site approach, for the recovery of photocatalytic activity of photocatalytic oxidation filters after challenging ultra-violet photocatalytic oxidation systems with approximately 100 ppb of acetone or methyl ethyl ketone. Experimental observations of photocatalyst deactivation, and characterization of fresh and deactivated photocatalyst with the scanning electron microscope technique were presented. During the regeneration process, the production rates of formaldehyde, acetaldehyde, and acetone were hourly quantified under a short-term and a long-term ultraviolet C illumination. The regeneration performance was also examined and compared by testing the single-pass removal efficiency of regenerated photocatalytic oxidation filters by two methods: ultraviolet C illumination and O3-included ultraviolet C illumination. The results indicate that the ultraviolet C-induced regeneration method, superior to O3-assisted ultraviolet C method, plays a certain role in partial recovery of the photocatalytic activity. The degree of recovery would depend on the nature of contaminant gases previously processed in ultra-violet photocatalytic oxidation since different VOCs generate various types and amounts of surface adsorbed by-products, which resist regeneration at a different level. Graphical Abstract. UV-PCO represents a new generation technology for improving indoor air quality. However, little is known about photocatalyst deactivation and regeneration which is a major concern for the purpose of commercialization. The current objective is to explore the UVC-induced regeneration method, the simplest on-site approach, employed in an HVAC system. This work demonstrates a systematic evaluation of deactivation and UV-induced regeneration performance under the conditions relevant to the actual applications for two VOCs. In addition, the gaseous by-product generation rates and O3-assited UVC-induced recovery method were examined for the first time. GRAPHICAL ABSTRACT

Filtration of Nanoparticles Applied in General Ventilation

Nanoparticles (NPs) are particles with a diameter less than or equal to 100 nm. Because of their size, they pose a major challenge to workers’ health and safety. General ventilation is one of the solutions in order to minimize both occupational and general exposure. In North America, ventilation filters are tested according to ANSI/ASHRAE Standard 52.2 and rated according to their efficiency results as a function of particle diameter. The most penetrating particle size (MPPS) is commonly accepted as being 300 nm, but it no longer represents the worst-case scenario in terms of particle diameter and filter penetration. The purpose of this article is to compile an inventory of experimental knowledge on the performance of entire filters and their media. The scope of this experimental literature review is limited to studies of size-resolved penetration of media and entire filters published since 1980. Little information is available on size-resolved data for filters. The article also seeks to identify different trends by medium properties, particle properties, and operating conditions, particularly in terms of penetration and MPPS. These trends are already known for media, but more studies are still needed to determine whether the conclusions for media can be extrapolated to entire filters.

Airborne nanoparticles filtration performance of fibrous media: A review

Although the fundamental concepts of fibrous filters are clearly understood for the capture of micron and submicron sized particles, basic questions arise when the particles to be captured are nanometer-sized. The purpose of this article is to compile an inventory of knowledge on the performance of fibrous media for capturing nanoparticles. In the first part of this review, the classical theory of fibrous filters is described for media in general, with a focus on the principles that apply to nanoparticles filtration. The recent breakthroughs reviewed include theoretical and empirical models for single fiber efficiency. In the second part, we present the classical models of pressure drop for both clean and clogged flat fibrous media as applied to nanoparticles filtration. We also include an extensive discussion about pressure drop across a particle deposit (cake) during surface filtration. In the third part, the impact of several parameters such as air flow rate, humidity, particle shape and morphology, fibers diameter, heterogeneous fibers, electrostatic forces, upstream particle concentration and temperature are reviewed in detail.

Risk analysis for confined space entries: Critical analysis of four tools applied to three risk scenarios

ABSTRACT Investigation reports of fatal confined space accidents nearly always point to a problem of identifying or underestimating risks. This paper compares 4 different risk analysis tools developed for confined spaces by applying them to 3 hazardous scenarios. The tools were namely 1. a checklist without risk estimation (Tool A), 2. a checklist with a risk scale (Tool B), 3. a risk calculation without a formal hazard identification stage (Tool C), and 4. a questionnaire followed by a risk matrix (Tool D). Each tools structure and practical application were studied. Tools A and B gave crude results comparable to those of more analytic tools in less time. Their main limitations were lack of contextual information for the identified hazards and greater dependency on the users expertise and ability to tackle hazards of different nature. Tools C and D utilized more systematic approaches than tools A and B by supporting risk reduction based on the description of the risk factors. Tool D is distinctive because of 1. its comprehensive structure with respect to the steps suggested in risk management, 2. its dynamic approach to hazard identification, and 3. its use of data resulting from the risk analysis.

Validation of a Laboratory Test Bench for the Efficiency of an N95 Filtering Face Piece, using Simulated Occupational Exposure

Ultrafine particles (<100 nm) have special properties that nanotechnologies seek to exploit. However, due to their nanometric scale, these particles can be deposited in the lungs and cause damage. Based on current knowledge, occupational exposure to nanoparticles occurs mainly in workplaces handling nanomaterials, or when certain processes generate them indirectly. However, there are currently no limit values for exposure to ultrafine particles. To limit worker exposure, respiratory protective devices (RPD) are generally used. The aim of this study was to determine if (a) a laboratory test bench and (b) a simulated occupational exposure setup were reliable representations undesirable exposure in workplace. Thus, two tests benches were used to compare on the one hand conventional measurements and on the other hand sanding- simulation process measurements. NaCl aerosols were generated and then used to measure penetration with constant flow at 43 L/min, 85 L/min and 135 L/min, and one cyclic flow defined by 85 L/min as the mean inhalation flow. The results showed that initial penetrations were less than 5%, as required by the certification. The results also showed that there was a high correlation between the two penetration measurements. One also notes that the measurements had a slightly higher maximum penetration with a charge- neutralized NaCl aerosol than with an un-neutralized NaCl aerosol. The charged-neutralized particles constituted the worst-case scenario exposure.

Performance of ASHRAE models in assessing pollutant dispersion from rooftop emissions

The performance of different ASHRAE models besides their general development since 1997 forms the basis of this article. The experimental results of a few recent near-field pollutant dispersion studies are compared to those produced by ASHRAE models. These cases include isolated buildings and adjacent building configurations. In fact, ASHRAE can only be used to estimate rooftop dilutions on an emitting building and does not provide formulations to estimate dilutions on adjacent building surfaces. The results from this study show that ASHRAE models provide reasonable dilution estimates for low exhaust momentum ratios (M), while previous ASHRAE models predict lower dilutions than wind tunnel data for all cases. Furthermore, ASHRAE 2011 predicts reasonable dilutions on the leeward wall of the emitting building, which is an important contribution of the current ASHRAE model. It is suggested that future ASHRAE model versions should be capable of estimating reasonable dilutions on adjacent building surfaces for realistic urban scenarios, by taking into account the spacing between buildings.