Advances in particulate matter filtration: Materials, performance, and application

Air-borne pollutants in particulate matter (PM) form, produced either physically during industrial processes or certain biological routes, have posed a great threat to human health. Particularly during the current COVID-19 pandemic, effective filtration of the virus is an urgent matter worldwide. In this review, we first introduce some fundamentals about PM, including its source and classification, filtration mechanisms, and evaluation parameters. Advanced filtration materials and their functions are then summarized, among which polymers and MOFs are discussed in detail together with their antibacterial performance. The discussion on the application is divided into end-of-pipe treatment and source control. Finally, we conclude this review with our prospective view on future research in this area. (c) 2022 Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Face Masks and Prevention of Respiratory Viral Infections: An Overview

Airborne transmission of respiratory viruses consists of three sequential steps: (1) release of respiratory fluids in the form of droplets from the nose and mouth of an infected person, (2) transport of the droplets through air, and (3) entry of the droplets into the nose and mouth of an uninfected individual. Talking, coughing, and sneezing emit droplets across a spectrum of sizes. The water in exhaled droplets begins to evaporate in air and, as a result, the droplets are reduced in size shortly after being emitted. Face masks are effective for capturing droplets just released from the nose and mouth. Studies indicate that more than 50% of community transmission of SARS-CoV-2 is from asymptomatic and pre-symptomatic cases. Use of face masks by the public can effectively reduce the chance of infected individuals unknowingly spreading the virus. In addition to being an effective device for source control, face masks can protect the wearers from inhaling virus-laden droplets. Cloth masks and disposable masks provide reasonable protection for the public, while surgical masks and N95 respirators give higher levels of protection as needed in healthcare settings. Made with varied materials, these masks have different structural characteristics. The collection efficiency of a face mask depends on droplet size, face velocity, and the structural characteristics of the mask. For a given mask, capturing droplets is more effective during exhalation than during inhalation. Pressure drop across the mask should be taken into consideration when selecting a face mask. The best face mask is the one that gives the highest collection efficiency with the least pressure drop. For an effective protection, a mask should fit the face properly. While face masks have proven adequate in reducing airborne transmission of SARS-CoV-2 infections, continuous improvement is needed to better prepare for future respiratory viral threats. © The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

Face Masks and Prevention of Respiratory Viral Infections: An Overview

Airborne transmission of respiratory viruses consists of three sequential steps: (1) release of respiratory fluids in the form of droplets from the nose and mouth of an infected person, (2) transport of the droplets through air, and (3) entry of the droplets into the nose and mouth of an uninfected individual. Talking, coughing, and sneezing emit droplets across a spectrum of sizes. The water in exhaled droplets begins to evaporate in air and, as a result, the droplets are reduced in size shortly after being emitted. Face masks are effective for capturing droplets just released from the nose and mouth. Studies indicate that more than 50% of community transmission of SARS-CoV-2 is from asymptomatic and pre-symptomatic cases. Use of face masks by the public can effectively reduce the chance of infected individuals unknowingly spreading the virus. In addition to being an effective device for source control, face masks can protect the wearers from inhaling virus-laden droplets. Cloth masks and disposable masks provide reasonable protection for the public, while surgical masks and N95 respirators give higher levels of protection as needed in healthcare settings. Made with varied materials, these masks have different structural characteristics. The collection efficiency of a face mask depends on droplet size, face velocity, and the structural characteristics of the mask. For a given mask, capturing droplets is more effective during exhalation than during inhalation. Pressure drop across the mask should be taken into consideration when selecting a face mask. The best face mask is the one that gives the highest collection efficiency with the least pressure drop. For an effective protection, a mask should fit the face properly. While face masks have proven adequate in reducing airborne transmission of SARS-CoV-2 infections, continuous improvement is needed to better prepare for future respiratory viral threats. © The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

SARS-CoV-2 Surface Swabs in Locations With Public Access-Potential for Improved Source Control.

The presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on surfaces at public locations has been minimally described. By swab testing, we investigated the presence of SARS-CoV-2 on surfaces in public locations during the pandemic in February 2022. The viability of SARS-CoV-2 was not tested. Almost 25% of surfaces were positive for SARS-CoV-2; this was most pronounced in supermarkets.

Present Anti-pandemic Ventilation Measures and Application of Source Control Technology Based on Advanced Air Distribution

After the outbreak of COVID-19, it is worrisome that how to cope with the spread of the pandemic. Ventilation is the most important engineering control measure, ASHRAE, REHVA, SHASE and authoritative institutions in China have issued many documents on how to apply HVAC system to prevent and control the spread of COVID-19, and thus this paper summarizes the contents related to the ventilation rate and air distribution. Besides, traditional total volume ventilation has the disadvantages of insufficient ventilation rate, less efficiency for short-term exposure events at short range and high energy consumption during the pandemic. Source control based on advanced air distribution has the advantages of high control efficiency, personalized adjustable, fast response and high energy saving potential, which can make up the disadvantages of the total volume ventilation scheme. Therefore, this paper systematically summarizes the technical types of source control based on advanced air distribution in coping the spread of respiratory infectious diseases. Considering that the design of ventilation system in the post-pandemic era is facing the development of "combination of normal time and pandemic period", the advantages of applying source control in the post-pandemic era and the application schemes of source control in high-risk scenarios are discussed, and the directions that need to be further explored in order to implement the design concept of"combination of normal time and pandemic period" are also discussed. This paper aims to provide a reference for the compilation of subsequent guidelines, and to bring some new ideas and enlightenments to the ventilation design for future pandemic prevention. © 2022, Editorial Department of Journal of Hunan University. All right reserved.

Effect of Double Masking with Silk or Cotton Over-masks on the Source Control Capabilities of a Surgical Mask

In spite of the remarkable progress made in the development of safe and effective vaccines against COVID-19, deployment of respiratory protective devices remains vital for mitigating the transmission of SARS-CoV-2 during the ongoing pandemic. In this study, we evaluated double masking, which entails layering a fitted over-mask on top of a surgical mask. A previously validated manikin-based protocol was used to evaluate the performance of a surgical mask with an over-mask made of silk or cotton. We showed that double masking can significantly enhance the mask???s source control capabilities by reducing an aerosol emission from a coughing or sneezing wearer while maintaining a reasonable breathability and comfort level. The data obtained in this study, as well as the results recently reported by other investigators, suggest that an over-mask made of silk fabric has several advantages over one made of cotton. Moreover, silk over-masks have the added benefit of providing a reusable protective outer layer for surgical masks as silk is hydrophobic and increases aerosol particle collection. Not only can double masking reduce viral or bacterial transmission, but it can also promote surgical mask longevity, thereby reducing global waste and pollution associated with the use of disposable surgical masks. Finally, an additional study with five human subjects revealed no significant differences in perceived comfort (measured by proxies such as relative humidity, temperature, and CO2 level inside the mask) between single masking and double masking, as well as between double masking with either a silk or cotton over-mask.

Advances in particulate matter filtration: materials, performance, and application

Air-borne pollutants in particulate matter (PM) form, produced either physically during industrial processes or certain biological routes, have posed a great threat to human health. Particularly during the current COVID-19 pandemic, effective filtration of the virus is an urgent matter worldwide. In this review, we first introduce some fundamentals about PM, including its source and classification, filtration mechanisms, and evaluation parameters. Advanced filtration materials and their functions are then summarized, among which polymers and MOFs are discussed in detail together with their antibacterial performance. The discussion on the application is divided into end-of-pipe treatment and source control. Finally, we conclude this review with our prospective view on future research in this area.

Face mask fit modifications that improve source control performance.

BACKGROUND: During the COVID-19 pandemic, face masks are used as source control devices to reduce the expulsion of respiratory aerosols from infected people. Modifications such as mask braces, earloop straps, knotting and tucking, and double masking have been proposed to improve mask fit however the data on source control are limited. METHODS: The effectiveness of mask fit modifications was determined by conducting fit tests on human subjects and simulator manikins and by performing simulated coughs and exhalations using a source control measurement system. RESULTS: Medical masks without modification blocked ≥56% of cough aerosols and ≥42% of exhaled aerosols. Modifying fit by crossing the earloops or placing a bracket under the mask did not increase performance, while using earloop toggles, an earloop strap, and knotting and tucking the mask increased performance. The most effective modifications for improving source control performance were double masking and using a mask brace. Placing a cloth mask over a medical mask blocked ≥85% of cough aerosols and ≥91% of exhaled aerosols. Placing a brace over a medical mask blocked ≥95% of cough aerosols and ≥99% of exhaled aerosols. CONCLUSIONS: Fit modifications can greatly improve the performance of face masks as source control devices for respiratory aerosols.

The source control effect of personal protection equipment and physical barrier on short-range airborne transmission.

In order to control the spread of Covid-19, authorities provide various prevention guidelines and recommendations for health workers and the public. Personal protection equipment (PPE) and physical barrier are the most widely applied prevention measures in practice due to their affordability and ease of implementation. This study aims to investigate the effect of PPE and physical barriers on mitigating the short-range airborne transmission between two people in a ventilated environment. Four types of PPE (surgical mask, two types of face shield, and mouth visor), and two different sizes of the physical barrier were tested in a controlled environment with two life-size breathing thermal manikins. The PPE was worn by the source manikin to test the efficiency of source control. The measurement results revealed that the principles of PPE on preventing short-range droplet and airborne transmission are different. Instead of filtering the fine droplet nuclei, they mainly redirect the virus-laden exhalation jet and avoid the exhaled flow entering the target's inhalation region. Physical barriers can block the spreading of droplet nuclei and create a good micro environment at short distances between persons. However, special attention should be paid to arranging the physical barrier and operating the ventilation system to avoid the stagnant zone where the contaminant accumulates.

Unmasking the Mask: Investigating the Role of Physical Properties in the Efficacy of Fabric Masks to Prevent the Spread of the COVID-19 Virus.

To function as source control, a fabric mask must be able to filter micro-droplets (≥5 µm) in expiratory secretions and still allow the wearer to breathe normally. This study investigated the effects of fabric structural properties on the filtration efficiency (FE) and air permeability (AP) of a range of textile fabrics, using a new method to measure the filtration of particles in the described conditions. The FE improved significantly when the number of layers increased. The FE of the woven fabrics was generally higher, but double-layer weft knitted fabrics, especially when combined with a third (filter) layer, provided a comparable FE without compromising on breathability. This also confirmed the potential of nonwoven fabrics as filter layers in masks. None of the physical fabric properties studied affected FE significantly more than the others. The variance in results achieved within the sample groups show that the overall performance properties of each textile fabric are a product of its combined physical or structural properties, and assumptions that fabrics which appear to be similar will exhibit the same performance properties cannot be made. The combination of layers of fabric in the design of a mask further contributes to the product performance.

Efficiency of Community Face Coverings and Surgical Masks to Limit the Spread of Aerosol.

In the current pandemic context of COVID-19, people wear different types of masks, particularly in their workplace, to limit the spread of the virus. Depending on their activity and work environment, employees are required to wear community face coverings, cloth masks with a transparent windows, surgical masks, reusable masks, or respirators. The objective of this study was to evaluate the efficiency as source control of these masks, i.e., when worn to protect the environment from the spread of particles emitted by the wearer. An experimental test bench including a dummy head and a breathing simulator associated with a DEHS droplet generator emitting 1 or 3 µm particles in the exhaled stream is used. Source control efficiency is calculated from the total flux of particles emitted in the test section without and with a mask. Seventeen models of masks are tested. Three breathing rate conditions were studied: from rest to heavy breathing, with average rates of 13, 27, and 45 L/min. Source control efficiencies vary from one mask to another. Among community face coverings (seven models) the values ranged from 15.6 to 33.8% for a medium intensity breath. The efficiencies of surgical masks (three models) ranged from 17.4 to 28.3% for the same breathing cycle. The community face coverings and the disposable surgical masks present equivalent values of source control efficiency, respectively, 25.9 and 24.1% at 1 µm and 31.5 and 23.2% at 3 µm. The respirators show higher source control efficiency than the other types of masks (76.7% at 1 µm and 82.5% at 3 µm). The statistical analysis of the data shows no effect of the breathing flow rate and an interaction effect between mask type and particle size. No differences in source control were found for the two particle sizes or the different experimental breathing rates for the respirators and the surgical masks. But the community face coverings and the cloth masks with transparent window present a source control efficiency which increases with the particle size. Varying levels of efficiency were measured with higher source control for respirators than for other types of masks. In the context of a respiratory protection programme, they can provide an effective barrier to the spread of the virus. But these results show also that no mask can stop all the particles emitted by its wearer. Regardless of the type of mask, other barrier measures (ventilation, social distancing, and hygiene) are then necessary.

Risk of SARS-CoV-2 transmission from universally masked healthcare workers to patients or residents: A prospective cohort study.

In a multifacility prospective cohort study, we identified 116 acute care, 26 long-term care, and 67 rehabilitation patients who received direct care from a universally masked healthcare worker while communicable with COVID-19. Among 133(64%) patients with at least 14-day follow-up, 3 (2.3%, 95% CI, 0.77-6.4) became positive for SARS-CoV-2. Universal masking, embedded with other infection control practices, is associated with low risk of transmission of SARS-CoV-2 from healthcare workers to patients and residents.

Perception and practice regarding infection control measures in Radiology department during pre-COVID and COVID times-A survey among radiologists and a review of current concepts and literature.

AIM: In this study, we aim to evaluate the perception and practice of IPC measures by Radiologists during pre-COVID and present COVID times, while conducting a thorough review of current concepts and literature, to provide a standard operating procedure (SOP) for radiology operations. METHODS: This study was conducted by Department of Radiodiagnosis and Imaging, Kasturba Medical College, MAHE, Mangalore. After obtaining approval from the institutional ethics committee, and other required permissions, the Google form questionnaire was sent to 350 Radiologists via email and text during the period of May 2020. Data was collected by time-based sampling in the period of fifteen days during the end of the total lockdown time. RESULTS: 54% (n = 152) reported never attending a training session on (Infection Prevention & Control) IPC prior to the COVID-19 outbreak. The perception regarding IPC were found to be good among radiologists as majority of the respondents were correctly able to answer questions regarding IPC. 86% (n = 152) of the respondents believed that their knowledge on IPC has improved during the COVID-19 pandemic. However, it was revealed that majority of the respondents only started to practice appropriate contact and droplet / procedural precautions only after the COVID-19 outbreak. CONCLUSION: The present COVID-19 scenario coupled with the lack of knowledge and training regarding IPC amongst radiologists evident from the results of our survey, highlights the need for proper training and establishing standard operating procedures and best practices in IPC pertinent to modern radiology practice.

Intermittent occupancy combined with ventilation: An efficient strategy for the reduction of airborne transmission indoors.

It is important that efficient measures to reduce the airborne transmission of respiratory infectious diseases (including COVID-19) should be formulated as soon as possible to ensure a safe easing of lockdown. Ventilation has been widely recognized as an efficient engineering control measure for airborne transmission. Room ventilation with an increased supply of clean outdoor air could dilute the expiratory airborne aerosols to a lower concentration level. However, sufficient increase is beyond the capacity of most of the existing mechanical ventilation systems that were designed to be energy efficient under non-pandemic conditions. We propose an improved control strategy based on source control, which would be achieved by implementing intermittent breaks in room occupancy, specifically that all occupants should leave the room periodically and the room occupancy time should be reduced as much as possible. Under the assumption of good mixing of clean outdoor supply air with room air, the evolution of the concentration in the room of aerosols exhaled by infected person(s) is predicted. The risk of airborne cross-infection is then evaluated by calculating the time-averaged intake fraction. The effectiveness of the strategy is demonstrated for a case study of a typical classroom. This strategy, together with other control measures such as continuous supply of maximum clean air, distancing, face-to-back layout of workstations and reducing activities that increase aerosol generation (e.g., loudly talking and singing), is applicable in classrooms, offices, meeting rooms, conference rooms, etc.