key: cord-0846185-u0oweudw authors: Teesing, G.R.; Straten, Bart van; Man, Peter de; Horeman, Tim title: Is there an adequate alternative for commercially manufactured face masks? A comparison of various materials and forms date: 2020-08-05 journal: J Hosp Infect DOI: 10.1016/j.jhin.2020.07.024 sha: 83fc57add41f5d318a9a4046373ee2788a039431 doc_id: 846185 cord_uid: u0oweudw BACKGROUND: There is a worldwide shortage of medical grade face masks. Donning masks can play an important role in curbing the spread of SARS-CoV-2. AIM: To conclude if there is an effective mask for the population to wear in public that could easily be made during a medical face mask shortage using readily available materials. METHODS: We determined the effectiveness of readily available materials and models for making a face mask. The outcomes were compared with N95/FFP2/KN95 masks that entered the Netherlands in April-May 2020. Masks were tested to see if they filter a minimum of 35% of 0.3ɥm particles, are hydrophobic, seal on the face, are breathable, and can be washed. FINDINGS: Fourteen of the 25 (combinations of) materials filtered at least 35% of 0.3ɥm particles. Four of the materials proved hydrophobic, all commercially manufactured filters. Two models sealed the face. Twenty-two of the 25 materials were breathable at <0.7 mbar. None of the hydrophobic materials stayed intact after washing. CONCLUSIONS: It would be possible to reduce the reproduction rate of SARS CoV-2 from 2.4 to below one if 39% of the population would wear a mask made from ePM₁ 85% commercially manufactured filter fabric and in a duckbill form. This mask performs better than 80% of the imported N95/FFP2/KN95 masks and provides a better fit than a surgical mask. Two layers of quilt fabric with a household paper towel as filter is also a viable choice for protecting the user and the environment. The current SARS-CoV-2 crisis caused a worldwide shortage of medical grade personal protective 2 equipment, including face masks. Nevertheless, some governments, such as in Austria, Israel, 3 Singapore, and the Czech Republic, require(d) the population to wear a mask when outdoors, while 4 other governments suggest the use of face masks in public. [1, 2] This contradiction has led to the 5 improvisation of face masks out of readily available materials. fabric-based masks. The American and Belgian models optionally hold a filter, either a coffee filter 10 (United States) or not specified (Belgium). There are no published data available describing the 11 protection these masks provide to the wearer and/or the environment. Although there is contradictory evidence about protective effect of masks, meta-analysis concludes 14 that surgical and FFP2/N95 masks reduce the risk of SARS by approximately 80%. [7] We investigated 15 the production of an alternative, effective mask for the population to wear in public that can easily 16 be made during a crisis using readily available materials. We define effectiveness as the ability of the 17 mask to reduce the reproduction rate (R₀) of the virus to under one. There are few published studies investigating the efficacy of readily available materials for face 20 masks. One such article describes various commonly available fabrics for masks but omits 21 information about the form of the mask and the use of additional filters. [8] The authors tested the 22 filtration efficiencies and pressure drops for a surgical mask, vacuum cleaner bag, cotton t-shirt, 23 scarf, tea towel, pillowcase, cotton mix, linen, and silk. The two microorganisms which were used for 24 the filter efficiency tests were 0.023ɥm and 0.95-1.25ɥm. These tests showed that the fabrics filtered 25 49% to 90% of the microorganisms at 0.023ɥm. Quesnel describes the benefits of a particular cotton 26 J o u r n a l P r e -p r o o f (1) Can be produced at home from widely available fabrics, including commercial air filters and 1 materials which are available at a fabric or grocery store; (2) Filters a minimum of 35% of particles at 0.3ɥm; (3) Has a seal on the face (at the level of an FFP2-mask); 4 (4) Is breathable; 5 (5) Is hydrophobic; 6 (6) Can be washed. For direct comparison, we used two commonly used masks as references: an FFP2/N95 mask and a 9 RII-surgical mask which were made to conform to European standards. [16, 17] 18 We chose filters based on a literature search, on which fabrics are promoted as filters by 19 governments, and by searching for readily available non-woven fabrics, although we are aware that 20 woven fabrics can possibly be effective. [3-5, 8, 20, 21] Commercial air filter fabric, made for heating, 21 ventilation and air conditioning (HVAC) systems, were considered a viable option, since they are built 22 to filter out particles with ranging from 0.3 to 10ɥm in diameter. We hypothesized that filter material care were avoided, since this could cause new shortages in the health care system. We hypothesized 26 J o u r n a l P r e -p r o o f that materials could be used to make a mask as such or as an inlay filter. Materials were therefore 1 tested by themselves and between two pieces of cotton quilt fabric. Masks were made with and 2 without a metal nose strip. Step 1: Particle test. A calibrated particle counter (Solair 3100 Lighthouse, San Francisco, www.golighthouse.com, Figure 7 A.1) counted the number of free-flowing airborne particles in a one-minute cycle with a flow rate of 8 1.0 cfm. The measurement was conducted on particles of sizes 0.3, 0.5, 1.0 and 5.0μm. The closed 9 particle chamber is specifically built to conduct these tests. A baseline measurement was done before every material test, during which free-flowing air was 12 drawn into a particle chamber. The particle chamber was connected through a silicone tube to the 13 particle counter. Material was then clamped to the top of the particle chamber and we repeated the 14 test three times. The last measurement reflects total number of particles drawn into the particle 15 counter through the fabric. This test was repeated three times to ensure that loose particles on the 16 fabrics would not affect the filtration measurement. We calculated the ratio of particles that passed 17 through the material to the baseline measurement. This is an effective method for precise and fast Step 2: Fit test 21 Mask safety depends not only on the filtration, but also on the fit on the face. [16, 17] It is important 22 that air does not enter or exit from the top, side or bottom of the mask to guarantee that the air 23 always passes through the filter. We used an AccuFIT 9000 Respirator Fit Test apparatus 24 (https://accutec-ihs.com/accufit-9000, Figure A .2). This machine counts the number of particles in the face mask during a series of movements, creating stress on the seal of the mask, which is 1 compared to the ambient particulate concentration. After validation of the device, the face mask was equipped with an inlet to a tube. A flow is created 4 through the tube and the number of particles in the mask is counted. The fit test includes cycles for 5 normal breathing, deep breathing, moving your head from side to side, moving your head up and 6 down, talking out loud, and bending over. [25] The fit factor confirms the level of leakage and is 7 calculated as a ratio of the particles inside the mask relative to the ambient concentration outside 8 the mask. A fit factor of 100 or higher represents a good fit. All tests were done on one woman to 9 ensure homogeneity in the results. The mask prototypes were from either filter fabric only (ePM₁ 85%) or filter fabric (ePM₁ 85%) with 12 cotton quilt fabric. Different models were tested, such as folded, pleated, round, flat, and duckbill. Step 3: Pressure test 15 The pressure drop over the fabric was measured to ensure that the wearer of the mask can breathe 16 easily through the mask. A differential pressure sensor, type SDP2000-L, was attached to the particle 17 chamber. (Figure A. 1) The analogue differential pressure sensor is temperature compensated, 18 calibrated and has a resolution of 11Pa with a repeatability of 0.3% and accuracy of 1%. We The hydrophobic test compared the capacity of different fabrics to resist the penetration of fluids. Measuring wet particles can be seen as cross validation of the dry particle testing. plates. After incubation for 24 hours at 37 0 C, results were read by two independent readers as the 9 number of Colony Forming Units. An ordinary laboratory paper towel was used as a control; a IIR-10 surgical mask served as a reference. The amount of fluid applied was unrealistically high as compared 11 to exposure in a real-life setting. Step 5: Wash test 14 We tested the commercial filters for usability after washing at 90°C. Step 6: Determination of needed population compliance. 17 We determined which percentage of the population would need to wear the mask for the rate of 18 growth of disease to fall below 1. This was calculated as 0.352 divided by mask efficiency, assuming 19 R₀=2.4. Only breathable materials were included. Step 1: Particle test 23 Particle tests were done on potential mask materials and imported N95/FFP2/KN95 masks. (Table I, 24 Table A.1) The best performing commercially manufactured material was the ePM₁ 85%, either alone 25 or between quilt fabric. Of the more readily available fabrics, leather performed the best, followed by a folded coffee filter between quilt fabric, a folded household paper towel between quilt fabric, 1 and microfiber fabric. The figure indicates how our best performing self-made mask performed in respect to the 244 6 imported N95/FFP2/KN95 masks that we measured in April-May 2020. [26] This figure shows the 7 particle filtration efficiency for 0.3, 0.5, 1, and 5μm from lowest to highest. The X indicates the 8 filtration of the ePM₁ 85% commercially manufactured filter. Step 2: Fit test 13 Both the duckbill model with the seams on the inside and with the seams on the outside passed the 14 fit test. (Table II, Table A Step 3: Pressure test 20 We used the best mask from the fit test as the reference, the duckbill with the seam inside, for 21 calculating the pressure. (Figure A. 3) Of the manufactured filters, the F7, F9, and M5 showed equal 22 or less pressure than the 3M reference mask. (Table I ) Both the single and folded tea towels showed 23 equal or less pressure than the 3M reference mask. Step 4: Hydrophobic test 26 J o u r n a l P r e -p r o o f Results showed considerable differences between fabrics. Four of the five commercially 1 manufactured air filters outperformed the IIR-surgical mask (Table III) . None of the other readily 2 available fabrics performed as well as the reference mask. Step 5: Wash test 7 We tested all materials that we expected could be malformed from being washed at 90°C. The 8 manufactured filters, cleaning cloth, leather, static dust cloth, and felt were all malformed after 9 washing. Step 6: Determination of needed population compliance 12 The best mask from the fit test was used as the reference, the duckbill with the seam inside. In Table 13 I, we only included fabrics which were breathable. The percentage of the population which would 14 have to wear a mask in order to halt the spread of SARS CoV-2 ranges from 37% to 88%, depending 15 upon the fabric. From the masks made from manufactured filters, the percentage of the population 16 which would need to wear a mask ranges from 39% to 88%. If people would make masks from easily 17 available fabrics from the fabric store and/or grocery store, the reproduction rate could go below 18 one if 85% of the population would wear a mask from quilt fabric with a single layer household paper 19 towel. These masks are relatively inexpensive to manufacture. We estimate the cost of the materials 20 of a mask at approximately €0.50 (quilting cloth) to €0.60 (ePM₁ 85%). From the above measurements, we conclude that it would be possible to reduce the R₀ of SARS CoV-24 2 from 2.4 to below one if a minimum of 39% of the population wears a mask from ePM₁ 85% fabric 25 in a duckbill form. Other commercially manufactured filters could be used, but then a greater portion of the population would need to wear them in order to achieve the desired reduction in the spread 1 of the virus. This mask provides nearly as much protection as an FFP2 mask and would provide more 2 protection to both the user and the environment than a surgical mask. We saw that the mask 3 according to the specifications in our study is better than approximately 80% of all commercially 4 manufactured N95/FFP2/KN95 face masks now entering the Netherlands. This mask is hydrophobic 5 and not washable. We also found that the two layers of quilt fabric with a household paper towel as filter can be a 8 viable and sustainable choice for protecting the population as it is widely available and cleanable. Unfortunately, none of the mask designs in which a filter could be placed passed the fit test due to 10 leakage, although the duckbill form could be made with quilt fabric and a paper towel. Masks made 11 from quilt fabric and paper towel are not hydrophobic and therefore likely to be less effective. Thus 12 85% of the population wearing this type of mask may still be inferior to 39% wearing the ePM₁ 85% 13 fabric mask. Our tests are more specific than the European standards. For testing the filtering requirements, the 5 EN 149+A1 (FFP masks) states that material should be tested with a particle size distribution with a 6 0.02ɥm to 2ɥm equivalent aerodynamic diameter with a mass median diameter of 0. European standards may not be optimal for SARS-CoV-2, which can be carried by aerosol or droplet. 14 The WHO considers the minimum droplet size to be 0.5ɥm.[32] Two size ranges of SARS-CoV-2 15 aerosols have been found, one from 0.25 to 1.0μm, and another with a diameter >2.5 μm. [12] It 16 could thus be advisable to do filtration tests for 0.25μm particles. This is close to our measurement of 17 0.3ɥm. Only the duckbill shape passed the fit test, both with the seams on the inside as on the outside. This 20 could be partly due to that the duckbill design had few seams and thus fewer places where air could 21 enter or escape. Hypothetically some of the other models would work well if they had been glued 22 instead of/along with sewn. The breathability requirements for respiratory protective devices are clear in the European 25 standards. [17] The maximum permitted resistance (mbar) differs for FFP1, FFP2, and FFP3 masks, ranging from 0.6-1.0 for inhalation at 30 l/min, 2.1-3.0 for 95 l/min and is 3.0 for exhalation at 160 1 l/m. The norm for an FFP2-mask at 30 l/min is 0.7 mbar. Our test was able to measure at 28 l/min 2 and indicated that most masks showed a pressure drop below 0.7 mbar. Our study has some limitations. The filters used may not be representative of all filters in these 5 classes, in particular regarding the hydrophobic characteristics. We also performed new "state of the 6 art" tests, rather than the tests described in the European standards. Furthermore, we were not able 7 to test the filtration value at 0.25ɥm, which is the assumed smallest particle size with SARS CoV-2. 8 Nevertheless, we consider the filtration value at 0.3ɥm relevant. We also were only able to do the 9 pressure test at one value, whereas the European standards suggest testing the resistance at three 10 different values. This research should give more insight into the next steps in developing a mask for the general 13 population. It would be prudent to repeat the tests of the masks from commercially manufactured 14 filters after various sterilization processes. Similarly, it would be advisable to repeat the tests on the 15 quilt fabric mask with a single layer of household paper towel, both before and after it has been 16 washed, since there is evidence that the pores of the cotton fabric widen after washing. [33] We 17 would also suggest fit tests with quilt cloth and a paper towel using other mask designs. Our study strongly supports the use of commercially manufactured filters as the fabric for an 21 alternative face mask, specifically ePM₁ 85% in a duckbill form. We conclude that it is possible to halt 22 the growth of the spread of SARS CoV-2 if 39% of the population wore a mask from this material. This 23 material performs better than 80% of the N95/FFP2/KN95 masks entering the Netherlands. Which countries have made wearing face masks compulsory? Evidence for 4 transmission of COVID-19 prior to symptom onset Pre-symptomatic transmission of 7 novel coronavirus in community settings. Influenza Other Respir Viruses European Committee for Standardization. NEN-EN 14683+C1 (en): Medical face masks -9 Requirements and test methods Respiratory protective 11 devices -Filtering half masks to protect against particles -Requirements, testing National Institute for Public 15 Health and the Environment World Health Organization. Clinical management of severe acute respiratory infection when 19 COVID-19 is suspected detail/clinical-management-of-severe-acute-respiratory-infection-when-novel-coronavirus-21 (ncov)-infection-is-suspected Particle Size-Selective Assessment of 23 The authors like to thank Jonas Soons from Eska Filtertechniek for donating manufactured filters for 5 this study and assistance in mask designs, Hélène Voeten and Iris Bonnema for their assistance in 6 sewing the masks, and Han Veltman and Dick Wille for their innovative contribution to the 7 hydrophobicity test.