Scientists are testing daily necessities to find the best protective measures against the coronavirus. Pillow cases, flannel pajamas and origami vacuum bags are all candidates.
Federal health officials now recommend using fabric to cover the face during the coronavirus pandemic. But which material provides the most protection?
The Centers for Disease Control and Prevention released seamless mask patterns made using handkerchiefs and coffee filters, as well as videos about making masks using rubber bands and folded fabrics found at home.
Although a simple face covering can reduce the spread of coronavirus by preventing foreign bacteria caused by coughing or sneezing of an infected person, experts say the extent to which homemade masks can protect the wearer from bacteria depends on the suitability of the product Sex and quality. Materials used.
Scientists across the country have set out to identify everyday materials that can better filter microscopic particles. In recent tests, HEPA stove filters, vacuum cleaner bags, 600 pillowcases and fabrics similar to flannel pajamas scored high. Stacked coffee filters scored moderately. Scarf and handkerchief materials scored the lowest, but still captured a small number of particles.
If you don’t have any materials tested, a simple light test can help you determine whether the fabric is the ideal choice for masks.
Dr. Scott Segal, chair of anesthesiology at Wake Forest Baptist Health, said: “Put it under bright light,” he recently studied homemade masks. “If the light really passes through the fiber easily and you can almost see the fiber, then it is not a good fabric. If you are woven with a thicker material and the light does not pass through that much, that is what you want to use material.”
The researchers said that it is important to remember that the laboratory research was carried out under perfect conditions with no leaks or gaps in the mask, but the test method provides us with a way to compare materials. Although the filtering level of some homemade masks seems to be low, most of us (stay at home and social distancing in public places) do not need the high level of protection medical staff need. More importantly, any face mask is better than no face mask, especially if someone who has been infected by a virus but does not know the virus wears it.
The biggest challenge in choosing a self-made mask material is to find a fabric that is dense enough to capture virus particles, yet breathable and enough to actually wear. Some items touted on the Internet have high filtration scores, but this material will not wear out.
Wang Wang, assistant professor of environmental engineering at Missouri University of Science and Technology, worked with his graduate students on various combinations of multilayer materials, including air filters and fabrics. Dr. Wang said: “You need a substance that can effectively remove particles, but you also need to breathe.” Dr. Wang won the International Aerosol Research Award last fall.
In order to test daily materials, scientists use methods similar to those used to test medical masks, and everyone agrees that medical personnel who are exposed to high doses of the virus as a result of visiting infected persons should be exempted from expenses. The best medical masks-called N95 gas masks-filter out at least 95% of particles as small as 0.3 microns. In contrast, a typical surgical mask (made using a rectangular pleated fabric with elastic earrings) has a filtration efficiency of 60% to 80%.
Dr. Wang’s team tested two types of air filters. The HVAC filter that reduces allergies works best, with one layer capturing 89% of the particles and two layers capturing 94% of the particles. The furnace filter captures 75% of the water in two layers, but it takes six layers to reach 95%. To find a filter similar to the one tested, look for a minimum efficiency reporting value (MERV) rating of 12 or higher, or a particulate performance rating of 1900 or higher.
The problem with air filters is that they can drop tiny fibers that can inhale dangerously. Therefore, if you want to use a filter, you need to sandwich the filter between two layers of cotton fabric. Dr. Wang said that one of his graduate students made his own mask according to the instructions in the CDC video, but added several layers of filter material to the square scarf.
Dr. Wang’s team also found that when using certain commonly used fabrics, two layers provide far less protection than four. A 600-thread count pillow case can only capture 22% of the particles when doubled, but the four layers can capture nearly 60% of the particles. A thick woolen scarf filters 21% of particles in two layers and 48.8% of particles in four layers. The 100% cotton handkerchief performed the worst, accounting for only 18.2% when doubled, and only 19.5% for four layers.
The team also tested Brew Rite and Natural Brew basket coffee filters. When the coffee filters are stacked in three layers, the filtration efficiency is 40% to 50%, but their air permeability is lower than other options.
If you are lucky enough to recognize the quilt, ask them to make a mask for you. Tests conducted at the Wake Forest Regenerative Medicine Institute in Winston Salem, North Carolina, showed that homemade masks made with using stitched fabric worked well. Dr. Segal of Wake Forest Baptist Sanitation, who is in charge of this research, pointed out that quilts tend to use high-quality, high-count cotton. In his research, the best homemade masks are as good as surgical masks, or slightly better, and the tested filtration range is 70% to 79%. Dr. Segal said that the filtration rate of homemade masks using flammable fabrics is as low as 1%.
The best performing designs are masks made of two layers of high-quality heavyweight “quilt cotton”, two-layer masks made of thick batik fabric, and inner layers of flannel and outer layers. Double-layer mask. cotton.
Bonnie Browning, executive director of the American Sewing Manufacturers Association, said that quilts prefer tightly woven cotton and batik fabrics, which will stand up over time. Ms. Browning said that most sewing machines can only handle two layers of fabric when making pleated masks, but people who want four layers of protection can wear two masks at a time.
Ms. Browning said that she recently came into contact with the quilt on Facebook and heard the voices of 71 people, who made nearly 15,000 masks in total. Ms. Browning, who lives in Paducah, Kentucky, said: “Our sewing machines are very complicated.” One thing most of us have is hiding fabrics.
Those who do not sew can try the folded origami mask created by Jiang Wu Wu, an assistant professor of interior design at Indiana University. Ms. Wu is known for her breathtaking folding artwork. She said that since her brother suggested in Hong Kong (usually when wearing a mask), she started to design a folding type with a medical and construction material called Tyvek and a vacuum bag. Masks. it. (DuPont, the manufacturer of Tyvek, said in a statement that Tyvek was designed for medical clothing rather than masks.) The foldable mask pattern is available online for free, and the video demonstrates the folding process. In tests conducted by the University of Missouri and the University of Virginia, scientists found that the vacuum bag removed 60% to 87% of the particles. However, some brands of vacuum bags may contain fiberglass or are more difficult to breathe than other materials, so they should not be used. Ms. Wu used a bag from EnviroCare Technologies. The company stated that it does not use glass fiber in its paper bags and synthetic fiber bags.
Ms. Wu said: “I want to create a choice for people who don’t sew,” she said. She is talking to various groups to find other materials that are effective in folding masks. “In view of the shortage of various materials, even the vacuum bag may run out.”
The standard thickness used by the scientists conducting the test is 0.3 microns because this is the measurement standard used by the National Institute of Occupational Safety and Health for medical masks.
Linsey Marr, an aerosol scientist at Virginia Tech and a virus transmission expert, said that the certification method for respirators and HEPA filters focuses on 0.3 microns, because particles of this size are the most difficult to capture. She said that although it may seem counterintuitive, particles smaller than 0.1 micron are actually easier to capture because they have a lot of random movement that makes them hit the filter fibers.
“Even if the coronavirus is about 0.1 microns, it will float in various sizes ranging from 0.2 to several hundred microns. This is because people release the virus from the respiratory droplets, which also contain a lot of salt. Proteins and other substances,” Dr. Marr, even if the water in the droplets evaporates completely, there is still a lot of salt, and proteins and other residues remain in the form of solid or gel-like substances. I think 0.3 microns is still useful for guidance because the minimum filtration efficiency will be around this size, which is what NIOSH uses. ”