Level 3 Surgical masks are loose-fitting masks that are commonly used by people and healthcare professionals in normal settings. They are made of a multi-layered structure, typically 3-4 layers of nonwovens. The outer layers are made of spunbonded polypropylene and the middle filter media is made of melt-blown polypropylene. The center layer is ionically charged to effectively capture the 0.1 µm aerosol. The typical weight of the nonwovens used is 20-25 gsm. The outside layer of the mask is hydrophobic, and the inside layer of the mask is made hydrophilic. These surgical masks should be produced based on ASTM F2100 standard. Summary of ASTM F2100 standard requirements for L3 surgical masks is as follows:
Standards: We selected the ASTM F2100-19 standards for our design.
Fabric: We tested a number non-woven fabrics that have a resilient local supply chain. We found that spunbond or melt-blown polypropylene with a thickness in the range of ~90 GSM have the right breathability and particle/droplet rejection capacity. We achieved this in a 3-ply format, with the inner ply being charged by plasma treatment. We found charging to be critical.
Based on our reteaches, the following materials are good candidate for L3 surgical masks:
Usability: We consulted with an experienced physician in our community, who kindly volunteered to test a number of samples produced to comment on comfort and breathability.
Manufacturing: We partnered with local sportswear manufacturing company, Niko. Joe and the team at Niko have been extremely helpful in doing small batchs and frequent design changes.
This is what some of the earlier prototypes look like.
We have a team that is racing to build an ASTM level 3 equivalent test setup. Our team has developed a breathability (pressure drop) test setup based on ASTM standard which is functional now.
Furthermore, the team has developed an ASTM approximation test setup for particle filtration efficiency. This setup is functional too.
The third test setup that our team is developing is for bacteria filtration efficiency. The design stage for this setup is finished and it is in the building stage now. We will post the design and BoM, and pictures here shortly.
Meanwhile, we have been lucky to receive particle filtration efficiency studies from APC Filtration in Brantford, and Kinectrics in Toronto, who even volunteered the first round of services (Thanks, guys!).
We found that electrostatic charging of the fabric is crucial for the fabric. Here are some of the results:
Another critical test for surgical masks is the blood penetration test. To perform this test we have been collaborating with Cambridge Material testing in Mississauga. A mask made of 3ply spunbond polypropylene with 42 gsm weight has passed the blood penetration test, while 2ply of the same material did not.Here is one of the results:
Niko Apparel in Hamilton, ON has started production. We are also in constant contact with a few other manufacturers in and around Hamilton to scale up. We estimate the local healthcare system to need around 5,000 masks per day. We are also in contact with the city and other community members to create a community-based supply chain for long term care facilities, law enforcement and paramedics, and ultimately sick individuals.
The buyer, one of the community hospitals in Hamilton, is finalizing logistics to start receiving Tuesday. Fingers crossed!