Introduction: Protective Hood for Powered Air Purifying Respirators- PAPR's, PPE Personal Protective Equipment
Below are instructions for constructing personal protective equipment for medical professionals battling Covid-19. My daughter is a third-year resident at one of the larger Boston hospitals in internal medicine. Her friends, who are our friends, are Emergency Room Doctors, Pediatricians, and Anesthesiologists, and some are already struggling with a lack of basic protective gear.
We are trying to produce hoods to fit positive pressure respirators, PAPR, which stands for powered air purifying respirators. The low pressure, positive pressure, keeps contaminated air out (construction and woodworkers use similar devices to keep from breathing small, harmful particles).
Within a week very few emergency rooms or ICU's will be able to fully meet the standards of a normal day. When that happens, medical professionals will get sick as they have in China Italy and now in Spain. In the country of Spain there are 5000 sick doctors, there are 500 sick doctors in Madrid alone. Keeping the public safe starts with keeping doctors safe. We have the advantage, and luxury of a small head start. All of the medical outlets and industrial outlets will be scoured and empty in short order. There is no reason to expect that production will be ramped up in time to meet the impending surge.
Help us make hoods for our current waist mounted fan/ filters. If you have a local hospital that would use one then make hoods for them and we can try to get you a fan/filter with a battery and charger. If not, we can help you track one down.
Note on 4.11.20 I have made some changes to the top pieces to fit wider hoses from other brands of PAPR's. Let me know if you need those. Will not be able to update the drawings for a few days
Tightly woven fabric
(Tyvek dumpster bags or Tyvek housewrap) Demo bags need additional seams. Tyvek house wrap needs to be crumpled at different steps so that it is not so noisy. Other smooth fabrics. We made a couple out of medium duty white tarp and they came out nicely. We also used a lightweight vinyl from Sailrite called Stamoid.
Thin line, 1/8” paracord
for draw string, or ¾” elastic.
Plastic for the window
Can be: Clear plastic file folders, Clear plastic from overflow garment bags, Acetate sheet, Windows from old windsurfers or boat sails or boat enclosures. Sailrite has vinyl in 12 to 30 gauge. 12 gauge should be fine and easy to sew.
White 3m Duct Tape or Clear Gorilla tape
Regular Seam ripper, inevitable steps backwards
Blue tape or masking tape
Olfa type plastic box cutter knife
Thin sharpie type pens
Step 1: Print Patterns
Print the patterns, full sized (24 x 36) or tiled to 8.5 x 11 letter paper or 11x 17 Tabloid paper.
You can download patterns for each of these components below. I’ve laid them out so you can print them on 8.5x11 sheets,11 x 17 sheets (soon), or full scale 24 x 36 sheets. Please do not go out to get prints. The safest way is to tile whatever you can print.
Once you’ve tiled the papers together, cut around the outlines to use as stencils for cutting the materials. Then cut the parts, as well as the inner window hole on the face piece. You can also transfer to a stiffer paper or cardboard if you’re going to use the template multiple times. For the skirt there are (2) pieces, orientation does not matter. For the top of the hood they have to be mirror images.
Note: We will also make dimensioned drawings so that even printing is not needed. You can construct the shapes with a ruler and pencil.
Step 2: Sew the Upper Tube
The first step in sewing the upper tube is to put the two upper pieces together inside out.
Stack the two upper pieces inside out with the hanging loop between them. The hanging loop will be mostly hidden between the two pieces. Stitch the small seam first and then long outer seam. *If you are using the demo bags that tend to fray you have to sew a seam at front edge and at the edge of the eventual tube. You can also simply tape these edges.
Once you have these two seams finished flip the piece inside out.
Join the 3rd piece that makes the tube. Start back about 1 1/2 “ from the end. Sew one side and then the other. If you are using the demo bag sew a hem , fold over, to the front edge. When this is done you have the top tube that will deliver air to the front of the hood right down the user’s face so that they do not fog the window. **If using tyvek crumple this piece up and open it back up.
Step 3: Sew in Window
Now we’re going to sew in the clear plastic window so your doctor can see through their hood. First, cut out the window in the hood, and cut the plastic for the window. **If you are using Tyvek House Wrap then crumple it now. You can’t do it once the window is in place. it will be much easier to tape the window to the tyvek if you hold the tyvek with tape stretched along the top line of the window. Then, adhere the clear plastic window to the inside of the hood with your blue tape to keep it in place. Stitch the window onto the hood using two rows of stitches.
When taping the fabric try to only tape to the seam width of the fabric otherwise it can fray when you take off the tape. This is for positioning. When you are finished sewing it is not a bad idea to neatly tape all the way around the window to cover the edge of the fabric. This looks good with white 3M tape or Clear Gorilla tape. I tore or cut each strip in half lengthwise. Start at the bottom and go up so that each piece covers a lower piece like a roof shingle or a fish scale.
Step 4: Attach the Top Tube to Hood
This step is the most difficult it might be worth practicing sewing a circle to a rectangle as if you were making a duffel bag. To get the pieces to join you have to curl one of them up. The video will be worth watching. After a couple of passes it becomes much easier.
Line up the pieces with the straight front edges aligned. They should be outside to outside. Sew the line across the front. Check that the two ends align. Sew a tack, or short stitch and check the alignment of the far end. Now the tricky part. You are sewing the edge of the top tube around the curved end of the front panel. Start slowly and pull the pieces together as you go. One will have to curl up so that the 2 edges can meet. The volume will start to become apparent. Tuck the hose connector piece at the back of the top tube into itself so that you are less likely to sew it closed by accident. Now sew the other side. It will now look like an inside out helmet!!
Before you fold the hood right side out.... CHECK FOR HOLES! These are places where the 2 edges did not close properly. It is easy to fix now. If not tape over the holes when it is inside out. That works perfectly as well. Specially with smooth white tape or smooth clear Gorilla tape.
Step 5: Sew Skirt
The first step in sewing the skirt is to make the sleeve for the draw string. The skirt has 2 panels. If you cut it on a folded over piece of fabric with your pattern edge on the fold then you can cut both pieces at the same time and you have one less seam to sew.
Fold the top edge of the sleeve to the stitch line. I made a template for marking the stitch line 1 3/4” in from the top edge. Be careful with this line of sewing. If the sleeve ends up too small it is really hard to thread the draw string. You should end up with openings at the ends of both sleeves. Leave them open since they will be on the inside of the hood. Once the sleeves are done thread a thin rope or bungee into the sleeve. You can sew in wide elastic but that is more difficult. If you do the elastic should be 22” long in the un-stretched length. Stretch it to the full length as you go. I don’t really know how to do this so I am using 1/8” paracord. Tape a length of thread to a straightened coat hanger and feed the thread through the sleeve with the coat hanger. A bit of tape at the front end of the coat hanger will keep it from catching on the fabric. Next tie the thread to the rope. If you burn an end of paracord you get a little ball on the end that will keep the thread from slipping off. Do this outside with plenty of ventilation. Finish the skirt by closing the last seams or joining the two pieces if you did it that way. **If you use demo bags add a hem to the bottom edge.
Step 6: Sew Skirt to Hood
You are almost there. Slip the right side out hood into the inside out skirt. The drawstring sleeve sticks above the stitch line. The good outsides are touching each other. After you sew the seam, and fold down the skirt, the drawstring and its sleeve will be on the inside.
Line up the drawstring on one side so that it will be easy to reach.
At this point slip a big book under the machine so the tube can roll around the bottom end of the machine.
Start past one side of the window and go across the front towards the other side. This way you will have a smooth seam in the front. If the two tubes do not match exactly take a fold, or pleat, in the longer one to get them to match. Sew all the way around and you are finished! Clean up any dangling thread ends and wipe it down with a clorox wipe or disinfectant wipe.
Step 7: You Have Finished. Congratulations!
To make these work you need a working PAPR respirator. PAPR stands for Powered Air Purifying Respirator. One Fan/ Filter/Hose can be shared amongst 2 or 3 people in shifts. They should each have 4 or 5 hoods to rotate since the current data says the virus will not live on surfaces for more than 3 days. They should be wiped anyway. In addition there is plenty of room to wear an N-95 mask under one of these hoods to be extra cautious. The PAPR unit should be checked for filtration and air flow. This information can be found elsewhere at the CDC or at manufacturer's web sites. Many versions have filters rated HE, High Efficiency, or HEPA, High Efficiency Particulate Arrestor. Their level of filtration is equivalent to a half face or full face respirator with P-100 filters rated to trap 99.7 percent of particles 3 microns and larger. The N-95 mask is rated to trap 95 % of these particles. The N-95 mask has to be fitted perfectly to achieve this. The PAPR and hoods provide additional safety in that they create a positive pressure inside of the hood. No contaminated air can get to them as long as the filters are working properly. An even safer way to use these hoods is with Supplied air from a clean remote location. The positive pressure in these situations do not depend on filtration, only on air flow from a clean source. In wood shops this is often done by connecting to hoses attached to a compressor blower in a separate room. Each situation is unique and must be evaluated for safe operation. The hoods can breathe outwards but do not make them out of materials that are too porous.
Step 8: Acknowledgements:
A very nice and dedicated group of people have helped me to date to get this project launched..
Chris P. and Esther P. on the Beta tests. Chris on the excellent sketches. Kate M. and Ella K. on an early prototype. Jose R. on the Autocad files. Ben S. on this instructable and drafts of how to present it. Lisa C. on the overall process. A very nice group at Sailrite with some test fabrics and windows. Two Doctors who need not be named who gave advice and even tried some of this on. Thank you to all of you.