In order to help bridge the gap in personal protective equipment (PPE) we created a 3D printed adapter to connect 3M P100 respirator filters to Ocean Reef snorkeling masks. Quantitative testing has shown that when connected properly with putty and gaskets, the filters can turn the snorkeling mask into an effective piece of protective equipment for those helping with the SARS-CoV-2 (COVID-19) Pandemic response.
Disclaimer: We present these results for information purposes only. The 3D printed adapter and the snorkel mask modification does not produce certified PPE or medical equipment. The authors of this page and their employer, Washington University in St Louis, waive all responsibilities regarding use and application of the information contained on the page.
COVID-19 crisis has resulted in a shortage of personal protective equipment
(PPE) . COVID-19 is currently the leading cause of death in the United
States. Health care providers caring for COVID-19 patients or at high risk
of being exposed to the SARS-CoV-2 virus benefit from a face shield to protect
against aerosol droplets that could hit the face and minimize the chance of
inadvertently touching the face with contaminated hands, and air filtration to
filter out aerosolized SARS-CoV-2. Adapting commercially available full-faced
snorkel masks (as Ocean Reef did here) have been proposed as an alternative to narrow the gap in PPE, to provide a combination face shield and filtration system. In this project we quantify the air filtration quality achieved with a full-faced snorkel mask, using a 3D printed adapter to attach commercially available 3M P100 particulate filters to an Ocean Reef snorkel mash provide air filtration.
1. Alltucker, K. 'Can't expect nurses to be miracle workers': Mask, equipment shortages push nurses to brink across nation. USA TODAY, 2020.
2. Geggel, L. COVID-19 is now the leading cause of death in the United States. LiveScience, 2020.
We tried to make an adapter for both 3M and Honeywell P100 filters. The 3M bayonet adapter is a simpler design that was fairly easy to print with FDM or SLA printers. However, the threaded Honeywell part has proven far more difficult. In PLA we basically gave up on this working. The threading precision is critical or there can be leaks between the adapter and filter. We are attempting to print it with an SLA resin printer (photo below), but still had issues passing the fit test.
The testing equipment consisted of a PortaCount 8030 Respirator Fit Tester (TSI, Minnesota, USA), Particle Generator 8026 Tester (TSI, Minnesota, USA), Surface Pro (Microsoft, Redmond, WA), Nellcor OxiMax N-65 Pulse Oximeter (Medtronic, Minnesota, USA) (Figure 1), and a gauge manometer (Instrumentation Industries, Inc., Pennsylvania, USA). The PortaCount 8030 was calibrated March 6, 2020 by TSI.
Figure 1. From left to right: A) pulse oximeter, B) SurfacePro, C) PortaCount 8030, D) ARIA QR+ snorkel mask, and E) particle generator 8026.
Testing was done in an approximately 9 ft. x 9 ft. room with the particle generator on. A 3M 6800 series (3M, St. Paul, MN) full-faced mask served as the benchmark.
Full face snorkel-mask
An Aria QR+ (Ocean Reef, Inc., California, USA) Medium/Large full-faced snorkel mask was tested since the design minimizes fogging problems and CO2 rebreathing.
A hole was drilled into the mask and a PortaCount grommet for testing N95 masks was inserted. Silicone was added to seal the external and internal surfaces. Crazy glue was used to secure and seal the contact between the metal grommet and plastic tube to reduce air leaks that can impair accurate quantification of the fit factor.
For filtration we selected a 3M P100 particulate filter with 99.97 % filter efficiency meeting NIOSH P100-series test criteria.
3D printed adapter
The adapter was a modification of the APA – Aria Protection Adapter available at the Ocean Reef website (https://oceanreefgroup.com/covid19/). The original adapter was designed to accept a 40 mm particulate air filter with 1/7 inch thread. The design was modified to accept two 3M P100 filters. We made an earlier prototype with a single filter but found it required too much breathing effort to use for long durations. The CAD design is available here: https://www.tinkercad.com/things/7dZnjwUKZRr The design reduced the printing material required compared to a vertical alignment of the filter.
The adapter prototype was a black polylactic acid (PLA) print. PLA prints are porous and without an airtight coating they will not work in an air filtration application. Two coats of XTC-3D (Smooth-On, Inc., Pennsylvania, USA) were applied to make it airtight. One 3M 3PRG7 (3M, St. Paul, MN) inhalation port gasket was placed at each of the two inhalation ports. Finally, one P100 filter was attached at each of the two inhalation ports. Sticky putty (Alcolin, Cape Town, South Africa) was used to ensure an airtight seal between the mask and the snorkel connector.
Fit testing was performed using the OSHA 29CFR1910. 134 protocol in the PortaCount 8030. The fit test exercises include normal breathing, deep breathing, turning the head side to side, moving the head up and down, talking, grimace, bending over, and normal breathing. Each test exercise lasts one minute except for the grimace exercise which is 15 seconds. A passing fit factor for full face masks like this design is 500, while for half face masks is 100. The fit factor is expressed as the challenge aerosol concentration outside the respirator divided by the challenge aerosol concentration that leaks inside the respirator during a fit test. Therefore, the higher the number the better.
Daily QA for the PortaCount with the particle generator active was performed and passed. We tested the 6600 series 3M mask as our benchmark and three experimental configurations of the snorkel mask. These four experimental setups were named as follows:
We adapted the dual design for two Honeywell North filters, or one 22mm ventilator filter. We have only performed quantitative testing with the 3M design yet but will update this log with the results once we've done the others. All three designs are here. We tested the 3M design printed in PLA and coated in XTC 3D coating. We're also printing in e-Rigid PU resin on an EnvisionONE printer (EnvisionTEC). This is a semi-flexible airtight material that should be able to be used without coating. We will confirm and post back after quantitative testing, but prints look very nice!
We next made a dual filter design to increase air-flow and enable easier use of the mask. We chose a 3M P100 particulate filter with 99.97 % filter efficiency meeting NIOSH P100-series test criteria. While this is an excellent filter, it has become hard to find so we will look into adapting our design for other filters.
Fit testing was performed using the OSHA 29CFR1910. 134 protocol in the PortaCount 8030. Here is the equipment used in the test:
The fit test exercises include normal breathing, deep breathing, turning the head side to side, moving the head up and down, talking, grimace, bending over, and normal breathing. Each test exercise lasts one minute except for the grimace exercise which is 15 seconds. A passing fit factor for full face masks like this design is 500, while for half face masks is 100.
The 6800 series 3M mask served as our benchmark and reached its maximum fit factor in 1:15 minutes. O2 Saturation remained stable. Real time test results can be seen here:
This configuration passed the fit test results with a fit factor of 32281. Increased humidity decreased the comfort of the mask although fogging was minor.
Subjective user experience
A radiation therapist wore the mask from 9 AM to 3 PM while performing daily work activities which require an increased level of exertion while positioning and moving patients to the treatment couch of the linear accelerator. She took off the mask for lunch and for a break to have a drink. Visibility was great and comfort better...
We next modified the adapter provided by the Ocean Reef group (more info on that adapter can be found here) to include a single 3M P100 filter:
We printed this in PLA to test the fit.
While the fit was good, a test user found it took too much effort to breathe through a single filter (this is likely why most commercially respirators use two filters). We decided to adopt a 2 filter design for our next test.