Introduction: COVID-19 Swim Mask HEPA PAPR
***UPDATE 4/13/20 - We are updating our PAPR. We felt that the air flow coming from the computer fan was not enough, so we are using air pumps for inflatable raft toys. With this we hope to increase the volume of filtered air produced to make more positive pressure.
***UPDATE 5/1/20-We fit tested the PAPR unit. The Swim Mask PAPR has undergone in real-world use with excellent results
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 have designed and created 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 12v DC pool inflatable pump using by a 11.1v R/C drone battery. 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
- Full face swim mask
- 1 1/8" flexible bilge tubing- Home Depot
- 12v DC air pump for inflatables-big box stores/Amazon
- 11.1v LiPo battery- same voltage but smaller amperage than battery used in example
- balance charger for LiPo battery
- XT60 connectors
- LiPocharging bag
- LiPo battery voltage checker
- DC potentiometer
- HEPA vacuum bag
- duct tape
- electrical tape
- 3D printed parts
Step 1: Choosing the Mask
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. Our mask, like most full face swim masks, has a silicon valve below the chin where air can escape under positive pressure when you exhale or when pressure builds inside the mask.
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, and the lateral openings as exhalation ports. In the previous build we plugged the exhalation ports forcing air out the bottom of the mask only. On version 2, we decided to include the exhalation ports in the new adapter.
Step 2: Fitting Hose to Mask
We printed an adapter for all three holes at the top of the mask to increase air flow with inhalation and exhalation. My son Connor designed the front end of the adapter to fit the intake and exit holes at the top of the mask and the rear end of the adapter to fit the 1 1/8" tubing. The fit is snug from the mask to adapter and also from adapter to tubing, however electrical tape and duct tape can be applied to the junction of the tubing to mask adapter for an airtight seal.
Step 3: Supporting the Hose-mask Joint
The 3D printed mask adapter bridging the hose to the mask’s snorkel opening goes from a large diameter to a smaller one and is at risk for breaking. We wanted to support the hose at this critical juncture. Fortunately our mask, like many other full face masks, had a GoPro attachment on the top. We 3D printed pieces to work with the GoPro attachment and support the hose.
Step 4: Powering the PAPR
Instead of a computer fan, we used a 12v DC air pump for an inflatable raft. After the initial build we tested our 5v fan unit for airflow and found what other users had also discovered, which is the 5v computer fan air flow is too weak. Despite being rated at >30cfm we were not getting these volumes when testing how quick the fan would fill a garbage bag. We spent days trying to tweak the fan output by increased voltage and different power sources, but the community and commentators were correct and the fan output too weak, and we had to abandon the 5v computer fan. In searching for a suitable replacement we came across an old 12v air pump for pool inflatables. These too can can be found almost anywhere in big box stores such as Walmart and Target and also local pool stores and Amazon. It's important to use the 12v DC pump and not a 110v AC pump. If the plug cannot fit the cigarette adapter in a car, DO NOT USE IT because that fan will not work. See the picture above for the the correct type of plug confirming the pump is a 12v DC pump. The 12v plug was cut and removed after identifying which lead was positive and which was negative. The negative wires are connected to the two lateral leads of the adapter. The positive wire is connected to the lead at the tip. The positive and negative leads of the pump were connected to the +/- motor terminals of the potentiometer. This pump gave us more air flow but we needed a higher voltage battery to power the 12v pump. We used a 11.1v lithium polymer (lipo) battery commonly used in RC cars and drones as a power source for the pump. Our battery had a female XT60 connector so we mated it to a male XT60 connector and ran the positive and negative wires to the +/- power terminals of the potentiometer to vary the voltage delivered and control the speed of the fan.
***As an additional safety measure we added a LiPo battery voltage checkerwhich sits on the battery's 'tail' (not shown) to the PAPR unit to continuously monitor the status of the LiPo battery.
Step 5: Setting Up the HEPA Filter
Unfortunately we damaged the vacuum filter of our original build and could not trust that it was a reliable filter adequate for protection from small virus particles. After our initial build and purchase of the vacuum filter cartridge, we could no longer purchase the vacuum filter cartridge either because of the lack of stock or because maybe they had been purchased widely for this purpose. Regardless, we switched to a filter using a cut HEPA grade vacuum bag similar to the design of our HEPA vacuum bag filter in our non-powered design.The new filter design consists of two identical 'cones' attached to the 1 1/8" tubing. One cone attaches to the tubing leading to the pump and the other cone attaches to the tubing leading to the mask. In between the tubing is the smaller cylinder and the 5" diameter cut HEPA grade vacuum bag filter. Using a hamburger analogy, the two cones are the buns and the cylinder is the meat. The HEPA filter is the lettuce. Place them together to have a functional filter where the only air to reach the mask is now filtered by our HEPA vacuum bag. We secured the filter apparatus together with duct tape
Step 6: Putting It All Together
The filtered air hose was attached to the top of the mask.Turn on the fan via the potentiometer and you have your own PAPR. The potentiometer is necessary in this build to control the speed of the pump. At 100% it feels too fast and there is too much flow. The potentiometer setting at 51 (which we assume is 51%) feels like the flow of a traditional, commercial PAPR. The optimal settings however have not been calculated or validated. Again please make and use this device and these recommendations only in crisis mode as a last resort.
***In our non-powered swim mask filter build we used 2 additional filters, 3M P100 and Gibeck Iso-guard HEPA filterto protect against virus. We will make modifications to this version, version 2, of the powered swim mask HEPA filter build to try to use these commercial filters as well.
***As an additional safety measure we added a LiPo battery voltage checker which fits on the battery's 'tail' (not shown) to the PAPR unit to continuously monitor the status of the LiPo battery.
Step 7: Cons:
- The mask unit is loud. The fan creates a significant noise when running at a speed necessary for adequate air flow
- 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 swim mask HEPA PAPR and filters should only be used in PPE shortage crisis mode. ***The swim mask HEPA PAPR 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 have personally used the swim mask PAPR in real life procedures for several hours and it functioned better than expected. 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.
- The build may be complex depending on your comfort level with electronics and soldering, and 3D printing. Our non-powered swim mask build is less complicated with less parts
- LiPo rechargeable battery packs are not common for most and are inherently dangerous. Our original design called for a 5v fan powered by a everyday 5v powerbank, but the 5v fan proved to be too weak. By upgrading our fan we also needed to upgrade the power source to an 11.1v LiPo battery found frequently in R/C drones and cars. LiPo are safe when charged and monitored correctly with a balance charger and a fireproof LiPo bag, but care and respect must be taken when using this high charge density power source. ***We also added a LiPo battery voltage checker to continuously monitor the voltage status and prevent over discharge of the battery which may lead to hazardous results.
- 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 filter.
Step 8: Thoughts:
This device 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 powered HEPA filter you do so at your own risk. This device is 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 mask is easy to use and breathe in. The HEPA filter 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.
We like the use of the swim mask because it works as a face shield and creates a 'airtight' seal around the face. In the event there is not a complete seal, the positive pressure of the PAPR pushes air away from the mask preventing outside particles from gaining access to inside the mask. In addition those who have used a PAPR with the hood know how difficult it is to hear inside the hood with the fan on. Our design 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. The unit is also easily deconstructed and the mask can be washed with soap and water and/or appropriate cleanser and reused. *** As an aside, it just so happened on day 1 of using the mask in real-world conditions, I was accidentally splashed in the face with body fluids by the staff in the procedure room. Such events are rare, but do happen. Normally this may require stopping the procedure and eye-washing if there is any risk of contact to the eyes, but we were able to continue with a few wipes of disinfectant. After the procedure the mask was washed thoroughly with soap and water and the day continued as planned. Needless to say I was glad to have complete face protection that day compared to the standard a cloth based mask.
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.