Ali Bahloul | Concordia University (Canada) (original) (raw)

Papers by Ali Bahloul

Journal of Occupational and Environmental Hygiene

Institut de recherche Robert-Sauvé en santé et en sécurité du travail, 2019

Journal of Occupational and Environmental Hygiene, 2022

Aerosol Science and Engineering, 2019

Aerosol transport is a fundamental phenomenon in many environmental and industrial applications. ... more Aerosol transport is a fundamental phenomenon in many environmental and industrial applications. The study of the dispersion of aerosols, such as contaminants, in the workplace and the search for solutions to capture them are the biggest challenges currently faced in the field of occupational safety and health. In addition, laws and regulations that limit the level of worker exposure to contaminants in workplaces are becoming stricter. The aim of this study was to help reduce exposure to dust, including crystalline silica dust, emitted during the granite polishing process. During this process, the ultrafine particles generated are more difficult to capture than the fine ones, especially in rotational polishing, which causes the worst cases of dust exposure. An experimental test bench was set up to simulate ultrafine particle dispersion and assess three solutions for reducing worker exposure during the rotational polishing process. The use of the test bench allowed experiments to be performed while avoiding human exposure. Results showed that the test bench efficiently simulated the dispersion of ultrafine particle dust. Three solutions designed to reduce dust emissions, based on local exhaust ventilation, were evaluated on the test bench: a push-pull system, a dust shroud and a tool with integrated suction slots. They proved to be more than 95% effective. The results of this work highlight that the performance of local exhaust ventilation systems is very sensitive to the suction flowrate and the speed of the rotating disc, thus illustrating the complexity of dust removal associated with polishing processes in industrial environments.

The current work analyses the dispersion of pollutants in the near-field of a building with a roo... more The current work analyses the dispersion of pollutants in the near-field of a building with a roof exhaust stack for various building configurations. Through computational fluid dynamics (CFD) simulations, geometric parameters of adjacent buildings, such as height, length, width and spacing between buildings were evaluated. The study analyses, in qualitative terms, the impact of those geometric characteristics the risk of pollutant re-ingestion on buildings near the source. The main objective of the study is to suggest safe placement of air intakes on buildings facades in order to avoid or limit pollutant re-ingestion for different building configurations. The criterion for acceptability of safe intake placements was defined as the spatial location where normalized dilution, DN, is at least equal to 6. This value represents the acceptable threshold to avoid odors and occupational health effects for a large group of chemicals. In total, 25 different building configurations were simul...

PLOS ONE, Jan 23, 2023

While facing personal protective equipment (PPE) shortages during the COVID-19 pandemic, several ... more While facing personal protective equipment (PPE) shortages during the COVID-19 pandemic, several institutions looked to PPE decontamination and reuse options. This study documents the effect of two hydrogen peroxide treatments on filtration efficiency and fit tests as well as the side effects for volunteers after the decontamination of N95 filtering facepiece respirators (FFRs). We also propose an efficient and large-scale treatment protocol that allows for the traceability of this protective equipment in hospitals during PPE shortages. Methods The effects of low-temperature hydrogen peroxide sterilization and hydrogen peroxide vapor (HPV) on two FFR models (filtration, decontamination level, residual emanation) were evaluated. Ten volunteers reported comfort issues and side effects after wearing 1h FFRs worn and decontaminated up to five times. Results The decontamination process does not negatively affect FFR efficiency, but repeated use and handling tend to lead to damage, limiting the number of times FFRs can be reused. Moreover, the recommended 24-h post-treatment aeration does not sufficiently eliminate residual hydrogen peroxide. Prolonged aeration time increased user comfort when using decontaminated FFRs.

Science and Technology for the Built Environment, Jul 12, 2020

With an equal mass, nanoparticles (NP) have a higher toxicity than particles with the same chemic... more With an equal mass, nanoparticles (NP) have a higher toxicity than particles with the same chemical composition but with larger surface area. However, the toxicological knowledge concerning NP is still insufficient to establish limit values of exposure. To seek the lowest exposure level, filtration is a simple and effective way to capture particles, including NP. According to ANSI/ASHRAE 52.2 standard, ventilation filters efficiency is tested for particles ranging from 0.3 to 10.0 μm. Performances of entire filters for NP are still very limited and particle size of 300 nm (0.3 μm) is commonly used as the most penetrating particle size (MPPS) for mechanical media. In order to evaluate the filter performance for NP, five type of filters were investigated to measure their performance for particles smaller than 300 nm including NP. The performance of these filters was evaluated in terms of penetration and pressure drop. Experimental data permit to evaluate the MPPS for these mechanical filters. Nevertheless, 150-500 nm range provides a better estimation of the MPPS in the conditions which were tested. Also, filtration velocity influences efficiency for nanoparticles at 50 nm but no effect was observed for MPPS.

Advances in Building Energy Research, Dec 28, 2020

Vacuum cleaner is known as a proper way to remove settled dust or aerosols from surfaces to prote... more Vacuum cleaner is known as a proper way to remove settled dust or aerosols from surfaces to protect building occupants against abiotic and biological particles. In fact, the act of vacuuming the su...

Science and Technology for the Built Environment, Nov 9, 2018

Nanoparticles (NP) are particles with a diameter less than or equal to 100 nm. Because of their s... more Nanoparticles (NP) 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 paper 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 sizeresolved penetration of media and entire filters published since 1980. Little information is available on size-resolved data for filters. The paper 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.

Conclusions: For the five blade the pressure was low than 10 Pa during two seconds of simulation ... more Conclusions: For the five blade the pressure was low than 10 Pa during two seconds of simulation in Comsol Multiphysics. This pressure had the good agreement with dust behavior in the air during sucking. With the obtained pressure, dust conserved their mobility diameter during the injection in the diluter. References: 1. Djebara, Wenga, and Songmene, Pollutant Emissions control in the Machine Shops, EHS-02 (2012). 2. Wenga & al, (2012), Numerical study and simulation of dust sampling with dilution, Encyclopedic of research in Aluminium (2012). Figure 2. Domain of Palette suction pump and meshing. Figure 3. 2D and 3D simulation of average velocity field.

Aerosol Science and Engineering, 2020

Nanoparticles are defined as particles with at least one dimension in the range of 1-100 nm. Due ... more Nanoparticles are defined as particles with at least one dimension in the range of 1-100 nm. Due to the special properties of nanoparticles, they are used in many workplaces, thus leading to occupational exposure. Filtering facepieces (FFPs) are generally used in these workplaces to reduce the exposure. Many studies have measured FFP efficiency in laboratories using a scanning mobility particle sizer (SMPS). The aim of this study was to determine whether a NanoScan could be used to measure FFP efficiency against nanoparticles in workplaces for one type of N95 FFP. The results showed that the NanoScan gave maximum penetration and most penetrating particle size (MPPS) data for all configurations tested. Observations were consistent with those of previous studies: low penetration, MPPS smaller than 100 nm, and penetration increased as the airflow rate increased. The NanoScan gave a less precise MPPS and a slightly overestimated maximum penetration. These results confirm that the classic SMPS is a more precise instrument considering these two devices, whereas the NanoScan is faster to provide general information about the overall behaviour, which make it easy to use for a workplace environment. A NanoScan can thus be used as a first approach in workplaces.

Healthy, Intelligent and Resilient Buildings and Urban Environments, 2018

Volatile organic compounds (VOCs) are considered a major group of indoor air contaminants with se... more Volatile organic compounds (VOCs) are considered a major group of indoor air contaminants with several proven adverse health effects. Ultraviolet photocatalytic oxidation process (UV-PCO) is a promising technology for the removal of VOC contaminants in indoor air environments. In addition, adequate efficiency of PCO has been proven in laboratory conditions. However, when PCO is scaled up and applied in real conditions, there are some limitations that need to be addressed. Several factors are involved in the efficiency of the PCO process such as humidity, flow rate (residence time), inlet of contaminant concentration, light source, etc. To the best of our knowledge, most of the research conducted in this area has been performed in a bench-scale reactor with long residence times of several minutes and at high VOCs concentrations (hundreds ppm level), which are far from being real indoor conditions. The main objective of this research is to study the scaling effect on isobutanol removal efficiency under the conditions relevant to real indoor applications. For this purpose, full-scale (0.6 m × 0.6 m), pilot-scale (four parallel ducts, 0.3 m × 0.3 m each) and bench-scale (9 cm × 7 cm) test setups were used to study the VOCs removal efficiencies via PCO in the gas phase. First, three experimental setups for testing TiO2 photocatalyst are described. Then, the isobutanol removal efficiency is evaluated in the condition, which is close to the real application, considering the low-level contaminant concentration and high flow rate. The relative humidity in this study is kept in the comfort zone (RH ~ 50±5 %). The performance of UVC-PCO of the three scales is compared and discussed. For isobutanol with 0.003 mg/m 3 inlet contaminant concentration, around 24%, 56%, and 68% removal efficiencies were achieved in the full, pilot, and bench-scale systems, respectively.

Aerosol Science and Engineering, 2018

To characterize particle properties, a proper conditioning of aerosol samples is required for mos... more To characterize particle properties, a proper conditioning of aerosol samples is required for most aerosol measurement systems. Ultrafine particles are often generated in high concentrations, resulting in the need for dilution prior to measurement. Reasons for this sample dilution include the prevention of condensation of volatile compounds onto the particle surface, the suppression of chemical reactions and simply to bring the particle concentration below the maximum tolerable value for the measuring instruments. A number of different approaches are taken to dilute samples. In this article, a new type of dilution system designed for submicron aerosols with high concentrations is presented and its performance compared with design expectations. The new dilution instrument is based on a capillary/filter technique. Small capillary transports a tiny proportion of the sample and the greater part will be filtered and used as diluting gas. The shuffling between the two parts takes place inside a filter. Therefore, the dilution ratio is determined by the diameter of the capillary and the flow rate. With this principle, the dilution process is realized in a single step and on a fast time scale. Calibration measurements showed a linear relation between the dilution ratio and the control parameters within ± 2%. The dilution ratio was found to be independent of particle diameter in the size range between 10 and 400 nm. The dilution ratio scan for the proposed system can be varied continuously from moderate to very high dilutions (from 1:10 to 1:10 3); this range could be extended with minor modifications. The proposed instrument was built on a small and portable scale. The described dilution system opens a wide range of applications for particle sampling.

Chemical Engineering Journal, 2018

The application of photocatalytic oxidation (PCO) in VOCs degradation is greatly hindered at high... more The application of photocatalytic oxidation (PCO) in VOCs degradation is greatly hindered at high humidity levels. This is because VOCs compete with water molecules to adsorb on the generally hydrophilic photocatalyst surface, where photocatalytic reactions take place. Modified P25-TiO 2 nanoparticles with surface fluorination (F-P25) was prepared to reduce the surface hydrophilicity of Degussa P25. The prepared samples were characterized by BET, SEM, and XPS tests. Herein, the effects of surface fluorination on the adsorption capacity of P25-TiO 2 nanoparticles towards toluene, methyl ethyl ketone (MEK), and isobutanol, representing different classes of indoor air pollutants, were investigated. After surface fluorination, the adsorption capacity of modified TiO 2 was compared to bare-TiO 2 in a continuous reactor at four different relative humidity levels (i.e., 0, 20, 40, and 60%). Three adsorption isotherms, including Langmuir, Freundlich, and BET, were used to model the adsorption experimental data. The equilibrium data for the adsorption of all compounds showed the best fit with the BET model, and the Freundlich model also represented a good fit. Moreover, the results indicated that the surface fluorination of P25 increased adsorption capacity about two times for toluene in three humid conditions (0, 20, and 40%) compared to bare-P25. By combining the benefits of using an easy modification method by a low-cost modifier and using P25-TiO 2 , which is the most common commercialized photocatalyst, an effective method has been developed to enhance the efficiency of VOCs removal in indoor air environments.

Aerosol Science and Technology, 2009

In this article, numerical simulation of the Navier-Stokes equations was performed for the large-... more In this article, numerical simulation of the Navier-Stokes equations was performed for the large-scale structures of a two-dimensional temporally developing cylinder flow and the associated dispersion patterns of particles were simulated. The time-dependent Navier-Stokes equations were integrated in time using a mixed explicit-implicit operator splitting rules. The spatial discretization was processed using spectral-element method. Nonreflecting conditions were employed at the outflow boundary. Particles with different Stokes numbers were traced by the Lagrangian approach based on one-way coupling between the continuous and the dispersed phases. The simulation results of the flow field agree well with experimental data. Due to the effects of the coherent structures, the particles demonstrate a more organized dispersion process in the space and a periodic dispersion characteristic in the time. Particle dispersion increases with the flow Reynolds number and so does for particle concentration, which is independent of particle size. However, for particles at different Stokes numbers, the dispersion patterns are different. The particles at smaller Stokes number congregate mainly in the vortex core regions and the particles at larger Stokes number disperse much less along the lateral direction with the even distribution. The higher density distribution at the outer boundary of large-scale vortex structure characterizes the dispersion pattern of particles at the Stokes numbers of order of unity. Furthermore, these particles disperse largely along the lateral direction and show the nonuniform distribution of concentration.

Building and Environment, 2021

Abstract Reducing volatile organic compounds (VOCs) concentrations in built environments is neces... more Abstract Reducing volatile organic compounds (VOCs) concentrations in built environments is necessary to achieve acceptable indoor air quality or comply with workplace regulations. Different air cleaning technologies are applied for the removal of VOCs. Unlike conventional adsorption-based technologies like activated carbons, so-called electronic air cleaning (EAC) technologies generate reactive species directly or indirectly to oxidize VOCs. In this study, dynamic single pass tests were conducted in a test rig consisting of four identical test ducts with individual flow control, allowing simultaneous evaluation of four different air purification systems under identical conditions. Three oxidation-based air-cleaning technologies were considered: photocatalytic oxidation (PCO), non-thermal plasma (NTP), and ozonation (O3). A total of 17 different configurations of EAC systems were tested for acetone and/or methyl ethyl ketone (MEK) removal. These include 12 different commercial PCO units, one in-house pilot PCO, two plasma, and two ozonation units. Sixteen of them were tested for the removal of 0.1 ppm MEK and their single pass removal efficiencies varied from 0 to 37%. Eleven of them were examined for the removal of 0.1 and 1 ppm of acetone and the removal efficiencies were between 0 and 23%. Ozonation and PCO-based system using ozone generating vacuum UV lamps generally showed a higher efficiency than PCO-based system with non-ozone generating UVC lamps or plasma units. Formaldehyde, acetaldehyde, and acetone were detected as the oxidation by-products in MEK testing. PCO-based systems tend to generate more by-products.