Badger Shield

Universal PAPR hood design

April 17, 2020

Download the hood design and supporting documentation

The Badger Shield team has not rested since Lennon Rodgers, Director of the Grainger Engineering Design Innovation Lab at the University of Wisconsin-Madison, requested help to make face shields for the UW Health System in mid-March. You can read about our effort here.

While lots of cool stuff is still going on with the face shield, most of the team’s efforts have been redirected to developing a Powered Air Purifying Respirator (PAPR) Hood. Corin Frost, our Director of Visual Communications, let you into our early efforts in her blog post.

Now, we are happy to publish all our design files for the project. The zip file includes:

  1. A PDF that is the place to start. It has an overview of the features and functions, a bill of materials, instructions for sewing and assembly, 1:1 artwork of the material patterns and face shield, and a bunch of legalese that I recommend using to help put your kids to sleep.
  2. CAD files of the plastic fitting that connects to the PAPR blower hose. These are in STL format if you want to 3D print them (we recommend laser sintered nylon, but FDM and SLA should work, too), and STEP files if you want to import them into your CAD program to play with. Though we have not created any injection molds for these yet, we do have a molding strategy and all parts are drafted, so it should be ready to mold if you want.
  3. Reports on the material recommended to make the hood.
  4. A risk file and disclaimer. We have debated our regulatory and safety strategy endlessly and, in the end, we have reverted to a pure open-source model that intends to meet a critical need as quickly as possible. Any of you who decide to make these hoods must evaluate the risks individually. As you will see, our risk file does not yet include full design verifications and manufacturing SOPs that resolve some of the most critical hazards. We have great confidence in our design, and it has been co-developed with doctors (just like the face shield), so we believe that there is sufficient validation to support publishing the files.
Jesse PAPR Hood 1
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What is a PAPR?

Now a bit more context. PAPRs were originally designed for use in industry and manufacturing for activities like autobody painting, welding, and other tasks that create noxious fumes. They consist of a belt worn blower assembly that is battery powered. It uses a filter similar to the ones used in N95/N99 masks to filter room air and deliver it through a flexible hose to a fitting on the back of the hood. The air then inflates the hood, creating positive pressure that inhibits unfiltered air from entering the hood. The air then escapes through a neck opening into the clothes. Because PAPRs are an industrial tool, they are regulated by The National Institute for Occupational Safety and Health (NIOSH) and not the FDA.

At some point, hospitals realized this system would work well to protect against airborne disease. PAPRs were used extensively during the Ebola outbreak. The FDA then approved their use in hospitals.

How we got involved

In mid-March, UW Health contacted Rodgers with their top 10 needs for infection control. Number two on the list was a PAPR system. In early April, UW Health received 1,000 hoods from the federal reserve. At first, they believed these hoods would serve their needs if they were provided with an adapter to connect to a 3M blower hose. After further review, the lack of shoulder drape proved to be a deal breaker and they asked once more for the Badger Shield team to prioritize the creation of hoods.

The hoods are intended to be used by high-risk healthcare professionals, particularly for the anesthesia group to wear during intubations.

What’s unique about this hood

Primarily, this hood is not intended to be unique. It is intended to function identically to all of the well-designed and well-made hoods on the market. We used existing hoods as benchmarks while designing. We are trying to replicate what the Wall Street Journal is calling the “pop-up supply chain” to both:

  1. Fill the supply gap until the traditional supply chain can meet demand for hoods, especially for those smaller hospitals and practices that do not have immediate access to national stockpiles
  2. Help small businesses keep their brilliant and talented teams busy and employed making something that will help our healthcare heroes
  3. Attempt to shift our approach to emergency preparedness by reducing our reliance on low-cost imports

On the other hand, there is one important difference. This is intended to be a universal hood, capable of connecting to all hoses that come with the blower systems. Blowers can cost as much as $3,000. A hood costs about $60. While most hoods (including ours) can be cleaned and reused by a single user, they are less durable than the blowers, so there is a need for multiple hoods for every blower. As the UW realized, compatibility is a huge issue. If hospitals already have or can acquire blowers, they may struggle to find hoods that work with their blowers. With some ingenuity, it is possible to MacGyver a solution (duct tape comes to mind). But most doctors and nurses don’t want to rely on duct tape for protection.

Our solution is a universal threaded fitting that assembles across a hole in the hood. Between the male and female parts is a blower adapter, specific to different manufacturers. To date, we have created three unique adapters for 3M, Miller Electric, and RPB blowers. These were chosen specifically to address UW Health’s supply of blowers and we know there are many other blowers that need adapters.

Jesse PAPR Hood 2
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How you can help

To makers and manufacturers, we ask that if you or your customers need a different adapter that you use your design skills to measure the fitting you are trying to replicate and model it up using the SolidWorks 2019 file called “PAPR FITTING - NEW ADAPTER.SLDPRT” in the “SOLIDWORKS FILES FOR CREATING YOUR OWN FITTING ADAPTERS” folder of the zip file. There is a README file that explains the feature tree and molding strategy. Once you have a new design, we would really appreciate it if you can email the SolidWorks file you create to jesse.darley@delve.com. We will print one and try to verify that it works and then add to the open source database (with your permission.

Jesse PAPR Hood 3
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Obviously, you can also help by sharing this blog and a link to the Badger Shield website at the University of Wisconsin Makerspace so makers, suppliers and hospitals in need can fill out the intake form and join this project to make sure everyone that needs a PAPR hood has access to one.

Developing the PAPR hood with UW Health physicians.
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