Research Papers

This is a non-exhaustive list of research papers to help get you started:

 

CDC Suggested Reading on Homemade / DIY Masks

As of March 18, 2020, the CDC has linked to the following papers on its page, Strategies for Optimizing the Supply of N95 Respirators: Crisis/Alternate Strategies:

 

Mask theory to get you started

  • Respiratory Protection for Airborne Exposures to Biohazards
    N95 rated to block 95%+ of particles bigger than 0.3 μm. But the Coronoavirus is 0.1 μm in size. Why are healthcare workers using it, then it work? Virus is usually aerosolized by being attached to larger particles like respiratory droplets. N95 masks (and assumedly others of lesser quality) work by multiple mechanisms. Sometimes a mid-sized particle will get through while smaller and larger ones will be trapped.
  • Half-mask respirators are made for long-term industrial use. Includes instructions for decontamination with 70% isopropyl alcohol wipes, though you should not get the filter material wet. Note that half-mask respirators in general do not filter the exhalation. Thus they protect the wearer from everyone else, but not everyone else from the wearer.
    “Filters should be changed when they become clogged with particulate contaminant. The wearer can determine when this occurs as it becomes harder to breathe through the filters. The filters are designed to filter out particles in industrial conditions and in concentrations much higher than is likely to be encountered in a pandemic situation. It is therefore expected that one set of filters will cover at least one pandemic wave, after which they should be replaced for infection control reasons.”
    3M™ Reusable Half Masks for use in the Healthcare Industry
  • A longer paper, which has a nice section called “Isopropanol treatment,” which outlines how Isopropyl Alcohol (Rubbing Alcohol) is “known to remove electrostatic charges on filter media and to increase particle penetration in laboratory tests.” This is a BAD thing. So do not allow isopropyl alcohol to touch N95 or better filter units/media. These “electret” filters have an electrostatic charge to enhance filtering performance. Alcohol destroys this enhancement.
    Comparison of Nanoparticle Filtration Performance of NIOSH-approved and CE-Marked Particulate Filtering Facepiece
    Samy Rengasamy, Benjamin C. Eimer, Ronald E. Shaffer, Comparison of Nanoparticle Filtration Performance of NIOSH-approved and CE-Marked Particulate Filtering Facepiece Respirators, The Annals of Occupational Hygiene, Volume 53, Issue 2, March 2009, Pages 117–128, https://doi.org/10.1093/annhyg/men086
    • https://academic.oup.com/annweh/article/53/2/117/175361


Efficacy of Homemade / DIY / Open Source Masks

  • Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population
    “    Any type of general mask use is likely to decrease viral exposure and infection risk on a population level, in spite of imperfect fit and imperfect adherence, personal respirators providing most protection. Masks worn by patients may not offer as great a degree of protection against aerosol transmission.”
    van der Sande M, Teunis P, Sabel R (2008) Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population. PLoS ONE 3(7): e2618. doi:10.1371/journal.pone.0002618

 

Polypropylene (reusable shopping bag) surgical masks and possible DIY enhancements to filtering ability such as hydrocharging

  • Proposed technique – Make surgical masks (or filter media) out of reusable shopping bags (constructed of non-woven polypropylene). Then treat the mask fabric material to improve filtration performance by spraying both sides with water at 25 PSI (170 kPa) from a pressure washer / power washer / garden hose nozzle. Accelerating the drying time is less of an issue as this is not a mass production process and we are not planning to immediately put the fabric into large rolls. But do not apply heat.

  • Non woven polypropylene (NWPP) is commonly used in surgical masks and can be easily sewn into masks that can block the spread of droplets from coughs and sneezes.

    https://www.project-cloth-masks.com/ – Using non-woven polypropylene
    https://www.project-cloth-masks.com/about – Research

  • Use of a high pressure water jet to enhance the filtration capability of non-woven polypropylene (NWPP) is detailed in a 3M patent application. But this applies to microfibre webs (gauze like material with little threads that can be pulled apart), not the more unitary fabric of shopping bags, so this might not work at all. Note that a patent application (even if granted) is not proof that a technique actually works or works well, just some legal assurance that the technique is new, so we should dig up some research on actual efficacy. Always independently test new concepts from strangers on the internet.
    “Surprisingly, it has been found that merely by impinging these jets of water or stream of water droplets onto the nonwoven microfiber web, the web develops filtration enhancing electret charge. The charging can be further enhanced by subjecting the web to corona discharge treatment prior to impingement by the water. Preferably, the web is formed from melt blown polypropylene microfibers, poly(4-methyl-l-pentene) microfibers or blends thereof. The term “hydrocharging” will be used herein to describe this method.”
    “Each sample passed beneath the spray bar at a rate of 3.5 m/min, and was treated once on each face, vacuum extracted [Alex’s note: this is to speed up drying in mass production] and dried at 70 °C for one hour…hydrocharging (at pressures of at least about 170 kPa [Alex’s note: This is 25 PSI.]) develops useful levels of electret enhanced filtration characteristics”
    Method of charging electret filter media
    Agadjivand, S. A.; Jones, M. E.; Meyer, D. E. PCT International Application WO 9505501, 1995.
  • “Another method of charging which appears to rely heavily on triboelectric effects is hydrocharging (10). Hydrocharging involves the use of a high pressure water jet directed through a nonwoven filter media in order to impart charge. It is reported that quite good filtration media can be made using the hydrocharging technique (10). A drawback of the hydrocharging technique is the drying of the charged filters. If the drying is done at an elevated temperature, thermal charge carries are liberated within the dielectric leading to charge dissipation. If the web is insufficiently dried, the residual moisture can lead to fungal or bacterial contamination of the filter media during storage.”
    Electret Media For HVAC Filtration Applications
    By David L. Myers and B. Dean Arnold, Nonwoven Fabrics Research and Development, Kimberly-Clark Corporation, 1400 Holcomb Bridge Rd., Roswell, GA 30076


Treatments and Alternative Filtration Materials

  • I haven’t read this yet, but VERY interesting.
    “Here, we report the 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.”
    Quan, F., Rubino, I., Lee, S. et al. Universal and reusable virus deactivation system for respiratory protection. Sci Rep 7, 39956 (2017). https://doi.org/10.1038/srep39956


Surgical N95 vs. Standard N95