2008-2020: Advanced Testing
This material was put online April 2020 and revised May 2020.
This webpage is one portion of the greater exploration entitled "Cloth Face Masks: Merging Science & Home Remedies" that can be access at https://clothingtextiles.ualberta.ca/facemasks/.
Following the 2009 H1N1 flu pandemic, there has been more advanced testing regarding homemade cloth facemasks. Researchers still have an inability to address consistently (or at all) fibre content, thread count and weave structures in the research when addressing woven textiles. Wovens and non-wovens are also not addressed in terms of strengths and limitations. We continue to have categories that describe use of textiles such as "scarf," “tea towel,” “pillowcases,” and “T-shirt”―as if they were all created alike. The tests of homemade cloth facemasks produced by Davies et al. was thorough but only done on 100% knitted cotton homemade cloth facemasks. Nonetheless, the tests by Davies et al. are informative and build on the information gathered prior to this point.
3A. Pros & Cons
PROS
- LESSER PROTECTION BUT CAN BE SUFFICIENT TO REDUCE EPIDEMIC
“Homemade masks, and to a lesser degree surgical masks, are unlikely to confer much protection against transmission of small particles like droplet nuclei, but as the reproduction number of influenza may not be very high [14] a small reduction in transmissibility of the virus may be sufficient for reducing the reproduction number to a value smaller than 1 and thus extinguishing the epidemic [15].” (van der Sande, Teunis, Sabel, 2008: 4) - MASKS FOR ADULTS REDUCE AEROSOL EXPOSURE BUT RESULTS VARY. CHILDREN ARE LESS PROTECTED.
“All types of masks [personal respirators, surgical masks and homemade masks] reduced aerosol exposure, relatively stable over time, unaffected by duration of wear or type of activity, but with a high degree of individual variation. Personal respirators were more efficient than surgical masks, which were more efficient than home-made masks. Regardless of mask type, children were less well protected. (van der Sande, Teunis, Sabel, 2008: 1) “All masks provided protection against transmission by reducing exposure during all types of activities, for both children and adults (Table 1). Within each category of masks, the degree of protection varied by age category and to a lesser extent by activity. We observed no difference between men and women.” (van der Sande, Teunis, Sabel, 2008: 3) “…could imply that individual subjects may not always be optimally protected, from a public health point of view, any type of general face mask usage can still decrease viral transmission.” (van der Sande, Teunis, Sabel, 2008: 4) “However, overall these experiments show that significant protection against influenza transmission upon exposure can be conveyed also for lay people, including children, in spite of imperfect fit and imperfect adherence.” (van der Sande, Teunis, Sabel, 2008: 4) - HOMEMADE TEA TOWEL MASK (UNKNOWN FIBRE & WEAVE STRUCTURE) EFFECTIVE BUT ONLY HALF AS EFFECTIVE AS SURGICAL MASK FOR ADULTS
“Surgical masks provided about twice as much protection as home made masks, the difference a bit more marked among adults.” (van der Sande, Teunis, Sabel, 2008: 3) “…home-made masks such as tea cloths may still confer a significant degree of protection, albeit less strong than surgical masks or FFP2 masks.” (van der Sande, Teunis, Sabel, 2008: 4) - KNITTED 100% COTTON HOMEMADE MASKS BETTER THAN NO PROTECTION
“Our findings suggest that a homemade [knitted 100% cotton] mask should only be considered as a last resort to prevent droplet transmission from infected individuals, but it would be better than no protection.” (Davies et al., 2013: 413) - ONE THIRD EFFICACY OF KNITTED 100% COTTON HOMEMADE MASKS VS. SURGICAL MASKS
Knitted 100% cotton homemade masks and surgical masks “significantly reduced the number of microorganisms expelled by volunteers, although the surgical mask was 3 times more effective in blocking transmission than the [knitted 100% cotton] homemade mask.” (Davies et al., 2013: 413)
CONS
- USE MASKS TOGETHER WITH SEVERAL MEASURES, NOT ALONE
“…no matter how efficient at filtration or how good the seal, will have minimal effect if it is not used in conjunction with other preventative measures, such as isolation of infected cases, immunization, good respiratory etiquette, and regular hand hygiene.” (Davies et al., 2013: 417) “…it is important not to focus on a single intervention in case of a pandemic, but to integrate all effective interventions for optimal protection.” (van der Sande, Teunis, Sabel, 2008: 4) - ANATOMY, BEHAVIOUR & USE/DISPOSAL PROTOCOL AFFECT RESULTS
“The protective effect of masks is created through a combined effect of the transmission blocking potential of the material, the fit and related air leakage of the mask, and the degree of adherence to proper wearing and disposal of masks.” (van der Sande, Teunis, Sabel, 2008: 1) “…the presence of many different sources of variation, behavioural as well as anatomical, which can also be expected to be present if the general population would be requested to wear face masks in case of a pandemic.” (van der Sande, Teunis, Sabel, 2008: 4) - HOMEMADE MASK IS LAST RESORT
“An improvised face mask should be viewed as the last possible alternative if a supply of commercial face masks is not available, irrespective of the disease against which it may be required for protection.” (Davies et al., 2013: 417) - HOMEMADE MASKS MAY BE USED AS PROTECTION BUT NOT RECOMMENDED AGAINST INFECTION FROM AEROSOL
“Improvised homemade face masks may be used to help protect those who could potentially, for example, be at occupational risk from close or frequent contact with symptomatic patients. However, these masks would provide the wearers little protection from microorganisms from others persons who are infected with respiratory diseases. As a result, we would not recommend the use of homemade face masks as a method of reducing transmission of infection from aerosols.” (Davies et al., 2013: 417)
3B. Scholarly Findings and their Impact on Cloth Facemasks Making & Use
SIZE OF INFLUENZA PARTICLES & TRAJECTORY
- SMALL & LARGE PARTICLES: POTENTIAL TO BE SUSPENDED IN THE AIR, CAN TRAVEL CAN BE TRANSMITTED VIA DIRECT CONTACT (i.e. HANDS & SURFACES)
“Respiratory infections such as influenza are transmitted through infectious particles, small enough to be suspended in air [1]. Influenza transmission can occur via large droplets, which only remain suspended in the air for a short period of time thus requiring close contact, and can occur via small airborne particles, which remain suspended in air for considerable longer periods of time, and can thus be transmitted over larger distances [2]. Furthermore, some transmission may occur via direct contact with respiratory secretions such as on hands and surfaces [2].” (van der Sande, Teunis, Sabel, 2008: 1) - DAVIES ET AL. ADDRESS (INDIRECTLY) INFLUENZA VIRUS PARTICLES OF VARIOUS SIZES.
“The test organisms in this study can be used to estimate the efficacy of these masks against influenza virus because essentially any aerosolized particle will behave predominately in the air as a result of its physical characteristics rather than its biological properties (ie, influenza virus particles will travel in the air in the same manner as particles of an equivalent size). Therefore, as we have tested a viral pathogen smaller than influenza and a bacterial pathogen larger than influenza, we have tested the face masks with a suitable challenge across the size range of influenza virus particles.” (Davies et al., 2013: 416)
MASK DESIGN/FIT
- MATERIALS, FIT & LEAKAGE ARE IMPORTANT
“The protective effect of masks is created through a combined effect of the transmission blocking potential of the material, the fit and related air leakage of the mask, and the degree of adherence to proper wearing and disposal of masks.” (van der Sande, Teunis, Sabel, 2008: p. 1) “The fit of homemade masks, which could be e.g. made of a tea cloth or other comparable material available in the home, is likely to be even looser.” (van der Sande, Teunis, Sabel, 2008: 2)
==> The authors assume a good fit is not possible when made at home: has this been tested? Is it evidence-based? - DAVIES ET AL. PATTERN BASED ON SURGICAL MASK
“We devised a protocol for constructing a ‘’homemade’’ mask, based on the design of a surgical mask…” (Davies et al., 2013: 413) - DAVIES ET AL. FIT OF KNITTED 100% COTTON HOMEMADE MASKS HALF THAT OF SURGICAL MASKS
“The median-fit factor of the homemade masks was one-half that of the surgical masks.” (Davies et al., 2013: 413)
==> As not all homemade mass have the same design, this finding only applies to the design of the one tested by the authors. - ELASTIC MAY LEAD TO A BETTER FIT
“It was observed during this study that there was greater variation among volunteers in their method of fitting the surgical mask. The need to tie the straps at the back of the head meant that the surgical mask was fit in a variety of ways. In contrast, the face mask had looped elastic straps that were easier for the volunteer to fit.” (Davies et al., 2013: 417)
==> Ordinary people 1) may not have elastic handy at home and 2) the elastic may not sustain laundering, bleaching, microwaving as well as a cloth ties. - WITHOUT PROPER SEAL CAN LEAD TO NO BENEFIT
“Facemasks reduce aerosol exposure by a combination of the filtering action of the fabric and the seal between the mask and the face. The filtration efficiency of the fabric depends on a variety of factors: the structure and composition of the fabric, and the size, velocity, shape, and physical properties of the particles to which it is exposed.10 Although any material may provide a physical barrier to an infection, if as a mask it does not fit well around the nose and mouth, or the material freely allows infectious aerosols to pass through it, then it will be of no benefit.” (Davies et al., 2013: 416) - LIMITATION TO DAVIES ET AL. FIT TESTS
“Quantitative fit testing can only estimate the combined effects of filtration efficiency and goodness of fit. Although sensitive to particles with diameters as small as 0.02 um, it is not sensitive to variations in particle size, shape, composition, or refractive index. As a result, this method of fit testing does not allow the distinction between true bioaerosols and droplet contamination.” (Davies et al., 2013: 416)
MATERIALS
DEEMED SUITABLE:
- FILTRATION EFFECTIVENESS RELIES ON SEVERAL MATERIAL PROPERTIES
“…among other factors, filtration in respirators and masks depends on filter characteristics, including fiber diameter, packing density, charge of fibers and filter thickness, as well as particle properties, such as diameter, density and velocity10–14.” (Quan, Rubino, Lee, Koch, and Choi, 2017: 1). - VAN DER SANDE, TEUNIS, SABEL WITH TEA CLOTH (UNKNOWN FIBRE CONTENT & WEAVE STRUCTURE)
“… home-made mask (made of TD Cerise Multi® teacloths, Blokker).” (van der Sande, Teunis, Sabel, 2008: 2)
==> Why tea cloth were used for experiments in not explained. - PILLOW CASE (UNKNOWN FIBRE CONTENT & WEAVE STRUCTURE) & 100% COTTON KNIT: SUITABLE
“The pillowcase and the 100% cotton t-shirt were found to be the most suitable household materials for an improvised face mask. The slightly stretchy quality of the t-shirt made it the more preferable choice for a face mask as it was considered likely to provide a better fit.” (Davies et al., 2013: 415)
==> While knits can stretch, providing a more comfortable fit, the space between threads can get much larger than in certain woven fabrics. The ability to use woven textiles in a design that would provide a good fit was not addressed in Davies et al. - DAVIES ET AL. TESTED 100% COTTON KNIT MASKS ONLY
“All face masks were made with 100% cotton t-shirt fabric using sewing machines to speed construction.” (Davies et al., 2013: 414)
DEEMED UNSUITABLE:
- IF MASK MATERIALS/LAYERS MAKES IT TOO HARD TO BREATHE, UNFILTERED AIR MAY COME IN
“The pressure drop across a mask is a useful measure both of resistance to breathing and the potential for bypass of air around the filter seal. If respiratory protection is not capable of accommodating the breathing demands of the wearer, then the device will impose an extra breathing load on the wearer, which is especially impracticable for people with breathing difficulties. Furthermore, the extra breathing load may induce leakage owing to the increased negative pressure in the face mask.15” (Davies et al., 2013: 417)
==> This is important as people may have a tendency to construct a mask with too many layers thinking it will protect them more. Materials that make it too hard to breathe may have a negative impact as well. - VACUUM CLEANER BAG: UNSUITABLE
“The surgical mask had the highest filtration efficiency when challenged with bacteriophage MS2, followed by the vacuum cleaner bag, but the bag’s stiffness and thickness created a high pressure drop across the material, rendering it unsuitable for a face mask.” (Davies et al., 2013: 415) - TEA TOWEL (i.e. “STRONG FABRIC” OF UNKNOWN FIBRE CONTENT WITH A “THICK WEAVE”): UNSUITABLE BUT BETTER IN 2 LAYERS
“Similarly, the tea towel, which is a strong fabric with a thick weave, showed relatively high filtration efficiency with both B atrophaeus and bacteriophage MS2, but a high pressure drop was also measured [rendering it unsuitable for a face mask].” (Davies et al., 2013: 415). “…only the 2 layers of tea towel material demonstrated a significant increase in filtration efficiency that was marginally greater than that of the [100% cotton knit] face mask.” (Davies et al., 2013: 415) - TEA TOWEL (i.e. “STRONG FABRIC” OF UNKNOWN FIBRE CONTENT WITH A “THICK WEAVE”): UNSUITABLE
“Similarly, the tea towel, which is a strong fabric with a thick weave, showed relatively high filtration efficiency with both B atrophaeus and bacteriophage MS2, but a high pressure drop was also measured.” (Davies et al., 2013: 415) - DAVIES ET AL. LIST SEVERAL MATERIALS BUT NOT ALL REPORTED ON
==> Table 1 in the paper describes different materials that were tested For filtration efficiency and pressure drop: “100% cotton T-shirt,” “The "Scarf," "Tea towel,” “Pillowcase," "Antibacterial Pillowcase," "Surgical mask," "Vacuum cleaner bag," "Cotton mix," "Linen," "and "Silk.") (Davies et al., 2013: 414)
3C. Surface Coating & Care for Re-Use
COATING TO DEACTIVATE THE VIRUS -- ONLY TESTED IN THE LAB on polypropylene: according to Dr. Hyo-Jick Choi, a specific type of salt is needed.
- SODIUM CHLORIDE SALT IMPREGNATION
“…development of a universal, reusable virus deactivation system by functionalization of the main fibrous filtration unit of surgical mask with sodium chloride salt. The salt coating on the fiber surface dissolves upon exposure to virus aerosols and recrystallizes during drying, destroying the pathogens. […] Viruses captured on salt-coated filters exhibited rapid infectivity loss compared to gradual decrease on bare filters. Salt-coated filters proved highly effective in deactivating influenza viruses regardless of subtypes and following storage in harsh environmental conditions. Our results can be applied in obtaining a broad-spectrum, airborne pathogen prevention device in preparation for epidemic and pandemic of respiratory diseases.” (Quan, Rubino, Lee, Koch, and Choi, 2017: 1). “…to modify the surface of the fibrous filtration layer within masks with a continuous salt film for virus deactivation via two successive processes: i) salt is locally dissolved by the viral aerosols and ii) supersaturation is followed by evaporation-induced salt recrystallization. Consequently, viruses are exposed to increasingly higher concentrations of saline solution during drying and physically damaged by recrystallization.” (Quan, Rubino, Lee, Koch, and Choi, 2017: 1). (Quan, Rubino, Lee, Koch, and Choi, 2017: 2). - 5 MINUTES TO DEACTIVATE UPON CONTACT WITH SALT-COATED FILTERS
“…influenza virus was severely damaged on salt-coated filters even at 5 min of incubation. From microscopic analysis, aerosol drying time was about 3 min, indicating that destruction of virus observed at 5 min is associated with drying-induced salt crystallization. Physical damage of virus due to crystallization was similarly reported as a major destabilizing factor of inactivated influenza virus30,31. ” (Quan, Rubino, Lee, Koch, and Choi, 2017: 3). - COATING STILL EFFECTIVE UNDER HARSH ENVIRONMENTAL CONDITIONS
“The stability of salt coating on PP fibers was tested under harsh environmental conditions. Incubation at 37 °C and 70% relative humidity (RH) for 1 day did not cause any significant difference in filtration efficiency (t-test, P = 0.718) (Supplementary Fig. S8). As a result, all mice infected with dosage of penetrated virus through the filter stored at high temperature and RH displayed 100% survival with 7% of body weight loss (Fig. 4c,d). Even after 15 days of incubation, salts remained to coat PP fibers (Fig. 4e, and Supplementary Fig. S9a,b), despite change in grain orientation due to recrystallization (Fig. 4f, and Supplementary Fig. S10a,b).” (Quan, Rubino, Lee, Koch, and Choi, 2017: 3). - MIDDLE LAYER OF COMMERCIAL SURGICAL MASK RECEIVED SALT COATING
“…filtration efficiency refers to mask filters (middle layer)” (Quan, Rubino, Lee, Koch, and Choi, 2017: 7). “The commercial surgical masks had a three-ply structure. The middle layer is the filter media, whereas the inner and outer layers provide support and protect the filter against wear and tear. The metal nose clips and elastic ear loops were removed and circular samples (radius: 3 cm) were cut from the masks. The PP filters (middle layer) were isolated by removing the inner and outer protective layers (bare filters, Filterbare).” (Quan, Rubino, Lee, Koch, and Choi, 2017: 7).
==> Remove metals to address corrosion. - RECIPE FOR COATING & APPLICATION
“The coating solution was prepared by dissolving sodium chloride (NaCl; Sigma Aldrich, St. Louis, MO) in filtered DI water (0.22 μ m pore size; Corning, Tewksbury, MA) under stirring at 400 rpm and 90 °C, followed by the addition of Tween 20 (Fisher Scientific) to a final concentration of 29.03 w/v% of NaCl and 1 v/v% of Tween 20. To obtain the salt-coated filters, the mask bare PP filters were pre-wet to contain approximately 600 μ L of coating solution by incubating overnight at room temperature. Any remaining dry areas were removed by applying gentle strokes with tweezers to the filters while immersed in the coating solution. Subsequently, the filters were deposited in the desired volume of coating solution […] to control the amount of NaCl per unit area and dried in an oven (Isotemp Incubator, Fisher Scientific) at 37 °C for 1 day.” (Quan, Rubino, Lee, Koch, and Choi, 2017: 7-8). - DIFFERENT SALTS THAT CAN BE USED
“Notably, for demonstration of the concept of salt-recrystallization based virus deactivation system, NaCl salt was used, which has a critical RH of 75% at 30 °C35. However, salts with higher critical RH can be easily used, such as ammonium sulfate, potassium chloride and potassium sulfate, which have critical RH of 80%, 84% and 96.3% at 30 °C, respectively35. This suggests that salt-coated filters may be developed for specific environmental conditions.” (Quan, Rubino, Lee, Koch, and Choi, 2017: 7).
==> An article entitled "“The secret ingredient in this face mask that could prevent the next coronavirus? A dash of salt” in The Peterborough Examiner by Rosa Saba on February 12, 2020 (see https://www.thepeterboroughexaminer.com/news-story/9851340-the-secret-ingredient-in-this-face-mask-that-could-prevent-the-next-coronavirus-a-dash-of-salt/), included the mention of "people in China soaking their face masks in salt or saline solution," which was addressed by Dr. Hyo-Jick Choi, a biomedical engineer and professor in Chemical and Materials Engineering at the University of Alberta. Dr. Choi responded as such: "'No, it doesn't work like that," Choi said with a laugh, adding that not only are people using the wrong kind of salt, it's currently more important to properly use the masks available." The article mention the 2017 article ((Quan, Rubino, Lee, Koch, and Choi, 2017) and says that [as of February 12, 2020] a second paper has been submitted. Saba also mentioned how "Choi has obtained a patent for the product, and hopes to see it on the market in around 18 months." - LOW-COST TRANSFERABLE TECHNOLOGY
“This idea can be easily applied to a wide range of existing technologies to obtain low-cost, universal personal and public means of protection against airborne pathogens, such as masks and air filters in hospitals. Therefore, we believe that salt-recrystallization based virus deactivation system can contribute to global health by providing a more reliable means of preventing transmission and infection of pandemic or epidemic diseases and bioterrorism.” (Quan, Rubino, Lee, Koch, and Choi, 2017: 7).
CARE FOR RE-USE
- SECONDARY INFECTION DUE TO EQUIPMENT CONTAMINATION & DISPOSAL
“…safety concerns naturally arise about secondary infection and contamination from virus-laden filter media during utilization and disposal.” (Quan, Rubino, Lee, Koch, and Choi, 2017: 1). - BLOOD-BORN VIRUSES: MICROWAVE (FOR NOT LESS THAN 2 MIN. AT 600 W) EFFECTIVE
“…microwave irradiation, as a safe and effective method to reduce the risk of viral transmission. […] This study demonstrates the power of microwave irradiation for the reduction of viral transmission and establishment of this safety strategy could help reduce the transmission of blood-borne viruses.” (Siddharta, Pfaender, Malassa, Doerrbecker, Engelmann, Nugraha, Steinmann et al., 2016: 7) “…microwave irradiation for at least 2 min or longer at not less than 600 W is sufficient to reach a critical temperature which facilitates inactivation of HCV as well as HIV-1 or HCV/HIV-1.” (Siddharta, Pfaender, Malassa, Doerrbecker, Engelmann, Nugraha, Steinmann et al., 2016: 7)
==> This is statement is for “blood-borne viruses” and may not apply to influenza.
3D. Bibliography of Works Cited in this Section
Davies, Anna, Katy-Anne Thompson, Karthika Giri, George Kafatos, Jimmy Walker, and Allan Bennett. "Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?" Disaster Medicine and Public Health Preparedness 7, no. 4 (2013): 413-418. Cambridge University Press. https://doi.org/10.1017/dmp.2013.43
Quan, Fu-Shi, Ilaria Rubino, Su-Hwa Lee, Brendan Koch, and Hyo-Jick Choi. "Universal and reusable virus deactivation system for respiratory protection." Scientific reports 7, no. 1 (2017): 1-10. https://www.nature.com/articles/srep39956
Siddharta, Anindya, Stephanie Pfaender, Angelina Malassa, Juliane Doerrbecker, Michael Engelmann, Boya Nugraha, Joerg Steinmann et al. "Inactivation of HCV and HIV by microwave: a novel approach for prevention of virus transmission among people who inject drugs." Scientific reports 6, no. 1 (2016): 1-10. https://www.nature.com/articles/srep36619.pdf
van der Sande, Marianne, Peter Teunis, and Rob Sabel. "Professional and Home-made Face Masks Reduce Exposure to Respiratory Infections among the General Population." PLoS One 3, no. 7 (2008). doi: 10.1371/journal.pone.0002618