DIY masks

Background

This article will describe some of the requirements that should be considered by teams developing DIY masks to solve the lack of supplies during the Covid-19 pandemic.

Design considerations

Effectiveness

• Measurements in relation to graded masks (N95, N100). Results from literature still have a wide variety of ranges (10%-70%) for face masks, which serves to understand that not all DIY masks are made and wore the same.
• DIY evaluation (testing in experimental conditions and real use feedback)
• Adaptation to different face shapes and sizes: designs need to be adaptable or parametric.
• Good practices of making and using masks must be reproduced in order for masks to make sense.

Filter materials

• Industrial filters: some DIY designs are currently considering the use of HEPA filters. Consider questions such as the cost and availability of these filters in your location for sustained use by healthcare workers or the general population.
• Tea cloth or fabric layers: Some studies corroborate the feasibility of using layered fabric to make masks. Different considerations must be used when designing cloth masks.
• EVA filter: Some DIY projects have used EVA as a filter, due to it being a cheap and widely-available material.
• PLA or other 3D-printed materials: a current discussion has been raised around the porous quality of 3D-printed masks, which raises the question of whether they are the best material for home-made masks.

Cost and appropriateness

• Availability of materials: how easy are the materials easy to find? Are they found everywhere in the world?
• Overall cost: How much does it cost to reproduce.
• Easiness of documentation: are these masks fully reproducible? Are there variations in how people will make them?
• Lack of digital fabrication tools in certain areas can limit how these masks are made.

Hygiene

• Will they be reused/disinfected? Heat, UV light, water, soap, alcohol.
• Availability of replacement filters or masks.
• Microplastics from 3D printing having an effect on health due to a sustained use.
• Where does the humidity from the wearer's mouth go.

Comfort and ergonomics

• People will wear a mask for longer if they feel comfortable with it.
• More protective masks are less comfortable to breathe through.

DIY mask design literature review

The following literature will serve to evaluate design considerations for different types of masks, considering the surge of designs by

Some previous studies have evaluated the effectiveness of different homemade masks. While "none of these are as effective as a commercially designed face mask", they all offer some protection when other options are not available.

It could be argued that a cloth face mask design can be effective and therefore a recommended measure as long as the design is good and hygiene training is in place for all users.

CDC Blog: Non-occupational Uses of Respiratory Protection–What Public Health Organizations and Users Need to Know ^[1]

• Masks are likely to be worn incorrectly: independently of the mask used, a great part of the effort must be put into training the general population on the correct usage of masks.
• Fit tests must be performed for each user.

A cluster randomised trial of cloth masks compared with medical masks in healthcare workers ^[2]

• This study recommends against the use of cloth masks.
• "Penetration of cloth masks by particles was almost 97% and medical masks 44%."

Nonpharmaceutical measures for pandemic influenza in nonhealthcare settings—personal protective and environmental measures ^[3]

• Medical masks: "There is limited evidence for their effectiveness in preventing influenza virus transmission either when worn by the infected person for source control or when worn by uninfected persons to reduce exposure (...)"
• "Proper use of face masks is essential because improper use might increase the risk for transmission."

Evaluating the efficacy of cloth facemasks in reducing particulate matter exposure ^[4]

"When the cloth masks were tested against lab-generated whole diesel particles, the filtration efficiency for three particle sizes (30, 100, and 500 nm) ranged from 15% to 57%."

Simple Respiratory Protection—Evaluation of the Filtration Performance of Cloth Masks and Common Fabric Materials Against 20–1000 nm Size Particles ^[5]

• This article poses the dangers of single-layered cloth face masks, over a variety of materials.
• The level of instantaneous penetration is of 40%-90%.

Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population ^[6]

A study compared the effectiveness of three masks to prevent virus transmission: a home-made mask made from a tea cloth, a surgical mask, and Filter Facepiece Against Particles (FFP2). Subjects performed a variety of different physical actions. The study included both adults and children.

• FFP2 provided 50 times as much protection as home-made mask.
• A surgical mask provided 25 times as much protection as home-made mask.
• "Masks worn by patients may not offer as great a degree of protection against aerosol transmission."
• Regardless of mask type, children were less well protected.
• Masks were more effective at inward protection (to protect the wearer from the environment).

Fit Factors vs Protection Factors ^[7]

Protection factor can be divided in: 1. Fit Factor (FF): It is a simulation of workplace activities. It can be defined as the ratio of challenge aerosol concentration outside the respirator and the challenge aerosol concentration that leaks inside the respirator during the test. 2. Workplace Protection Factor (WPF): Actual level of protection during workplace use. 3. Assigned Protection Factor (APF): It is the level of protection expected of a mask on 95% of the time it is used.

Simple Respiratory Mask ^[8]

In this research, a home-made mask using eight layers of 2-ply t-shirt was tested for effectiveness and fit against a N95 mask. The most important take away from this paper is that fabric masks are less effective due to lack of proper fitting, but a good design of fabric mask from recycled T-shirts may be able to provide two thirds of the protection of an N95 mask.

• While N95 masks require fit factor of 100, this mask had a fit factor of 67.
• "(...) offered substantial protection from the challenge aerosol and showed good fit with minimal leakage."
• May be less effective when made by naïve users
• May be uncomfortable
• "No easy, definitive, and affordable test can demonstrate effectiveness before each use.”

Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic? Disaster Medicine and Public Health Preparedness ^[9]

• This study had subjects make their own masks.
• Regarding vacuum cleaner bags for masks: "bag's stiffness and thickness created a high pressure drop across the material, rendering it unsuitable for a face mask."
• Regarding cotton: "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."
• "Only the 2 layers of tea towel material demonstrated a significant increase in filtration efficiency that was marginally greater than that of the face mask."
• Surgical masks are still much better at filtering smaller particles.
• "It is likely that materials conditioned with water vapor, to create a fabric similar to that which has been worn for a couple of hours, would show very different filtration efficiencies and pressure drops."

Comparison of filtration efficiency and pressure drop in anti-yellow sand masks, quarantine masks, medical masks, general masks, and handkerchiefs. ^[10]

• From the abstract: "Medical masks, general masks, and handkerchiefs were found to provide little protection against respiratory aerosols."
• "For virus, some N95 respirators may fall below 95%" (level of effectiveness).
• Handkerchiefs over a person's face have 98% of penetration regardless of used material.
• Use of nylon hosiery material (“panty hose”) to hold the handkerchief material or the disposable face mask to the face was found to be very effective in preventing leakage (Cooper et al., 1983b). Such a combination could be expected to reduce leakage around the handkerchief to about 10% or less in practice, and around the mask to less than 1.0%.

Surgical Mask vs N95 Respirator for Preventing Influenza Among Health Care Workers: A Randomized Trial. ^[11]

This study found that the rate of infection was similar between surgical masks and N95 masks on a randomized controlled trial: "our data show that the incidence of laboratory-confirmed influenza was similar in nurses wearing the surgical mask and those wearing the N95 respirator. Surgical masks had an estimated efficacy within 1% of N95 respirators. Based on the prespecified definition, the lower CI for the difference in effectiveness of the surgical mask and N95 mask was within −9% and the statistical criterion of noninferiority was met. That is, surgical masks appeared to be no worse, within a prespecified margin, than N95 respirators in preventing influenza."

Physical interventions to interrupt or reduce the spread of respiratory viruses ^[12]

This is a literature review on best physical practices to avoid respiratory disases.

Use of cloth masks in the practice of infection control—evidence and policy gaps ^[13]

This article does not have any conclusive information

• Three factors were highlighted in these studies in regards to the filtration capacity of a cloth mask: 1) closeness of the gauze/cloth threads; 2) number of gauze/cloth layers and 3) type of gauze/cloth.
• Number of layers seems to increase the effectiveness of filtration in cloth masks.

Other studies and links

Infection Control for Viral Haemorrhagic Fevers In the African Health Care Setting "If surgical masks are not available, use cotton masks made from four or five layers of cotton cloth sewn together. Use a different colour for each side of the mask. This will help health care workers quickly identify which side should be worn inside."

Masks for Influenza Patients: Measurement of Airflow from the Mouth INOUYE SAKAE et. al. Jpn J Infect Dis 59, 3, 179-181 (2006) A study of the effectiveness of three simple commercially available (in Japan) face masks to reduce air speed of coughing and blowing. All masks, including a 16-ply, 10.7 g weight cotton mask reduced air speed of cough to less than 1/10.

Masks on fluwikie

• https://smartairfilters.com/en/blog/best-materials-make-diy-face-mask-virus/
• https://www.researchgate.net/publication/258525804_Testing_the_Efficacy_of_Homemade_Masks_Would_They_Protect_in_an_Influenza_Pandemic#pf7

Projects

• Twitter thread with projects

Other literature reviews

• A review of masks by User:LucasG
• DIY Masks Toronto
• FaceMasksReviews‎‎

References