Introduction: Covid-19 Swim Mask Non-Powered Filters X 3
***THIS IS AN ALTERNATE DESIGN RELATED TO THE Covid-19 Swim Mask HEPA PAPR
These are crazy times in the world of the COVID-19 pandemic. In my 24 years as a physician, I could never have imagined a time like now where we as a healthcare community and as a nation would be paralyzed by a disease leading to basic equipment shortages putting myself and colleagues in danger. Long before coronavirus, physicians and healthcare workers are used to putting our own lives and safety at risk in front of sick patients on a regular basis. Now, however, we are confronted with higher exposure risks of contracting the novel coronavirus in the absence of personal protective equipment (PPE). To minimize risk of contracting coronavirus from patients, front line healthcare workers can wear an N95 mask to filter small particulate matter. Unfortunately these masks have recently been in severe shortage. An alternative protective gear is the Powered Air Purifying Respirator (PAPR). A PAPR uses a motorized fan to pass air through a HEPA filter, which removes the contaminant and supplies purified air to a mask or hood. In response to the severe shortage of personal protective equipment that we face to protect ourselves form the novel coronavirus, my son Connor and I began by designing and creating what we feel is functional PAPR made out of a full face swim mask, tubing, computer fan, HEPA filter and 3D printed parts all powered by a 5V USB powerbank.
The original design was overall well received, but we realized that our build may be too complicated for some, or that there may be problems obtaining the necessary resources for the build. Here we describe alternate and simpler designs, again using the full face swim mask, to protect against the Covid-19 virus. We received requests to adapt the swim mask to different variations of protective filters, and the build is described here. Depending on your place of work and resources some or all of the following filters may be available to protect you:
- HEPA grade vacuum cleaner bag
- 3M P100 particulate filter for reusable respirators
- Gibeck Iso-guard HEPA filter for anesthesia mechanical ventilation circuit
Initially we started by making a different adapter for each filter to fit the mask. This was cumbersome and time consuming, so we decided to make a modular unit and have all three filters above connect to a simple, yet strong, 1/2" PVC elbow-schedule 40 commonly found in the hardware store. With this design, only one mask adapter needs to be 3D printed to fit any and all of the above filters. You will need the 1/2" pvc elbow and 3D print the appropriate adapter to each filter. Breathing is easier through these filters and the powered fan is not necessary.
Again, the goal was to make a device to protect those who put themselves in harms way to protect others. We wanted to make this mask with objects readily obtainable in the community, and with a few parts made from a 3D printer.
Just as with our previous design, we must stress that we share this with the maker community to be used as a last resort. Use of this mask and/or any homemade PPE should ONLY be performed as a crisis strategy as defined by the CDC when no other protective equipment is available. There are many communities and hospitals that have unfortunately reached this threshold. Their government and hospital have failed to provide the adequate bare necessities of protection that as healthcare workers we need in this fight against the coronavirus. We offer our design to help those who need protection, but understand, if you do use our design and any modification of it, you do so at your own risk. We cannot be held responsible for the quality of the parts you purchase or the print quality of your 3D printed parts. We are confident, however our design is superior in protection than the CDC recommended bandana.
Step 1: Choosing the Mask and Modular Adapters
We purchased a full face adult swim mask from Amazon. We felt that the swim mask designed to keep out water with a watertight seal is well suited to keep out the coronavirus.
We did not place the snorkel that came with the mask as the snorkel opening at the top of the mask would be used as the air intake. We identified the center opening as our air intake, however we printed an adapter for all three holes to increase air flow with inhalation and exhalation. My son Connor designed the front end of the adapter to fit the mask and the rear end of the adapter with a 0.84" round end to fit a standard 1/2" pvc elbow-schedule 40. For those paying attention, yes the inner diameter of the 1/2" PVC elbow is not 0.5" but 0.84" diameter (In case you thought the 1/2" diameter refers to the inner diameter of the pipe that would fit in the elbow , that diameter turns out to be 0.62"). Three 0.84" diameter adapters were then 3D printed and made available on thingiverse for the three new non-powered filters. Making a modular design connected to a 1/2" PVC elbow allowed us to quickly create adapters to various filters. Having the modular design with the PVC elbow adds strength to the joint better than we could achieve with 3D printing, and also allows any of the 3 filters to be rotated to clear the wearers head.
Step 2: Option - HEPA Vacuum Bag Filter
We described the efficiency of HEPA grade filters to filter out small particles the size of the coronavirus in our THOUGHTS section of our original COVID-19 Swim Mask HEPA PAPR. Using the same principle, we designed 3D printed pieces to securely hold a HEPA filter cut from a HEPA grade vacuum bag in the shape of a 3 1/2" - 4" circle.
We designed and 3D printed two parts for this project, the honeycomb cap and the 1/2" elbow adapter. The adapter has a round flared end where the HEPA filter will sit. The cut HEPA vacuum bag was placed on top of the larger end of the adapter, and it was secured between the adapter and the cap for a secure seal. The tight seal is necessary so that any airflow in the system moves through the HEPA and not around it. Attach the three piece HEPA filter unit to the other end of the 1/2" PVC elbow connected to the mask, and your mask is ready for use. Make sure all fittings and junctions are secure to prevent air leak. Duct tape around the junctions can add an extra layer of security for an airtight seal
Step 3: Option - 3M P100
We received requests to adapt our mask project to fit a highly breathable and excellent particle filter, the 3M P100. According to its specifications the P100 is superior to the N95 at efficiency of filtering out particles as small as the coronavirus. We were given a P100 and reverse engineered a 1/2" adapter to fit the P100. The 3D printed P100 adapter was inserted through the plastic cuff at the bottom of the P100 and turned 1/8-1/4 turn clockwise to get a secure fit. The P100 and adapter then are placed tightly on the PVC elbow attached to the mask, and the mask is ready for use. Make sure all fittings and junctions are secure to prevent air leak. Duct tape around the junctions can add an extra layer of security for an airtight seal
Step 4: Option- Iso-Guard HEPA Light Filter
Available in hospitals, but also for retail, is a small HEPA filter designed for use in the OR on ventilated patients. The filter is small and light, perfect for this mask project. An adapter to the Iso-Guard filter is made to attach the filter to the 1/2" PVC elbow. The elbow is attached to the mask and the mask is ready to use. Make sure all fittings and junctions are secure to prevent air leak. Duct tape around the junctions can add an extra layer of security for an airtight seal.
*** the filter shown on the adapter is NOT the Iso-Guard HEPA Light Filter described. It is similiar in size, shape, and connections and is shown for demo purposes.
Step 5: Cons
- The mask unit is non powered therefore airflow is dependent on the users inspiration. For some this can be difficult, but so is breathing through and approved N95 mask for an extended period of time.
- The mask unit has not been formally tested in the laboratory for efficacy and safety. As with our previous mask, we believe in the science and we believe the adapters that were designed and made by my son and I are a solid design. We would like to stress again that the non-powered swim mask and filters should only be used in PPE shortage crisis mode. That being said, all three non-powered units underwent unofficial OSHA standardized qualitative fit-testing by me and performed at least equal to an N95 using FT-32 Bitter as an agent. The only PPE tested to fail the qualitative test was the CDC recommended bandana. As a physician however, I know am putting my personal health on the line when I use any homemade device as PPE. I trust the science, work, and design that went into this build more than I trust the government and hospital systems to provide me and my colleagues with appropriate protection when we need it the most.
- You look funny. Let's be honest. To patients we may look ridiculous with this protective equipment but in crisis mode, you use what you have. My brother, an ER physician at a major California health system, is in the frontline in the battle with the coronavirus. Every day at work he is exposed and in crisis mode he is more than willing to use the swim mask and adapted filters, despite the fact that he feels he is wearing the a "pink USS Enterprise" on the top of his head.
Step 6: Thoughts
The use of the non-powered filters with a full face swim mask is sound in concept and theory but has not been tested. This device in no way is meant to replace existing and approved masks and devices such as N95 mask and commercial PAPRs when they are available. If you make this device or use the concepts of a wearable HEPA filter/P100 filter with a swim mask, you do so at YOUR OWN RISK. These devices are designed to be used as a 'crisis capacity strategy' for PPE as defined by the CDC when the surge in demand for PPE leads to severe shortage or unavailability of the approved protective equipment. As a physician, I have worn multiple types of N95 masks and PAPRs and I find our non-powered filter masks acceptable to breathe in. The HEPA filters and P100 should successfully filter the coronavirus. Although distance between fibers in the HEPA filter is 0.3 microns and the corona virus is smaller at .12 microns in size, the HEPA is able to filter close to 100% of coronavirus sized particles. The HEPA filter accomplishes this based on the multiple methods of capture the filter uses and the speed of which air is forced through the filter. Almost counter intuitively, the slower the velocity of the air passing through the filter, the more efficient the HEPA filter becomes at removing even the smallest particles in the air. Although very technical, the science behind this concept is illustrated here in this scientific paper by NASA engineers. In addition, The P100 by specification is superior in efficiency as compared to and N95 at filtering out particles the size of the coronavirus
Use of a mask instead of a hood leaves the ears outside the mask for better hearing. Because of this design, our mask can be used with a stethoscope, a feat that cannot be accomplished with a traditional PAPR hood or any hood. The unit is also easily deconstructed and the mask can be washed with soap and water and/or appropriate cleanser and reused. We also like the use of the swim mask because it works as a face shield and creates a seal around the face.
This project is a work in progress and will most surely evolve, as does our fight with coronavirus, and we will update the product design as we improve it. Any suggestions or comments are welcome.We understand that this build might not be for everyone as they may not be able to obtain the necessary resources and or have the technical capability to manufacture the device. For those who want to help in our fight I would like to direct you to Team Shield. We have partnered with Team Shield who are a an energetic group of students from Davis and Roseville California that have come up with a surprisingly simple yet brilliant solution to PPE equipment shortages. Their products and equipment are currently in use at Northern California hospitals. Please check them out because through Team Shield anyone can help our frontline healthcare workers by making shields or making donations.
Also we are not alone in innovation in making PPE as a crisis strategy. Please read these excellent articles from Make Magazine explaining how we ended up in crisis mode and a second article showcasing makers around the world sharing innovation to help us all battle coronavirus. As a physician I am not only humbled working next to my son in these projects originally started as a way to protect me and my colleagues facing crisis, but I am also humbled by the every-day makers and do-ers with no ties to healthcare trying to find ways to help healthcare workers and everyone else out of this mess we are in. We will survive, not with the promises of our government and healthcare systems, but in spite of them.