Powered Air-Purifying Respirator (PAPR)

What is it? What is its purpose?

This device is a lightweight powered air-purifying respirator (PAPR) that provides filtered air, face and eye protection, and skin surface cooling. These results are achieved without masking or requiring a large fan unit and air exchange tube, which are typical in most commercial PAPRs.

How does it work? What are its main features?

This device uses a small but powerful fan on top of the face shield to directly extract and filter surrounding air for the user to breathe in safely. This positive pressure, loose fitting device provides respiratory protection without requiring an air-tight seal. The user is able to adjust the fan speed to provide control of how much air is coming through for both ease of breathing and to control the amount of cooling experienced. The green power-on LED also adjusts in brightness based on the fan speed. If the power is disconnected for any reason, a bright flash from the red LED will be seen and the buzzer will sound indicating a loss of power.

Device Specifications:

• Weight: 220g
• Dimensions: 170x240x210mm
• Noise Level: 65dBA
• Max Airflow: 300 litres/min
• Filtration: HEPA 13 Filter
• Power: 5V 2.1A
• Device running time with 10,000mAh Battery: 8hrs

How long does it take to make and what skills are required?

3D printing on a Creality Ender 3 V2 Neo (~14 hours)

• Housing (~6 hrs 45min - 0.3mm layer height, 20% infill)
• Lid (~3 hours - 0.3mm layer height, 20% infill)
• Fan Funnel (~45 min - 0.2mm layer height, 100% infill)
• Inlet Filter Cap and Ring (~1 hr 15min - 0.2mm layer height, 100% infill)
• Outlet Filter Cap and Base (~2 hrs 15 min - 0.2mm layer height, 100% infill)

Electronic implementation (~1 hour)

• Wiring (~20 min)
• Soldering (~20 min)
• Testing (~20 min)

Attaching parts (~1.5 hours)

• Attaching the head strap (~15 min)
• Attaching the visor (~15 min)
• Cutting and sewing on the hood (~1 hour)

Where can I find more information about the research and development conducted for this device?

A design report is attached below which covers what is currently on the market and their associated issues, how this device is different and solves some of the common issues, and finally provides extensive detail about the research and development undertaken for this device.

If you have any questions, feel free to email [e-mail]

Supplies

The cost to make this device was $125.73 AUD ($85.53 USD). However, some parts were purchased in bulk. Therefore, based on the amount of material which was actually used, the cost can be reduced to $41.38 AUD ($28.12 USD). (See cost table attached below). If you can source the components cheaper elsewhere, feel free to do so. The main thing is that the electronic specifications and the type of filtration material are met.

Other Equipment

Hand Tools

• 25 Watt 240V Soldering Iron
• 10W Hot Melt Glue Gun
• Hole Punch Plier, Preciva Punch Hole Revolving Tool with V-Shaped Cutting, 6 Hole Sizes
• Kaisercraft Craft Scissors Green
• Wire Stripper 20-30 AWG Solid (22-32 AWG Stranded)
• Compass Drawing Tool
• Metal Ruler

Machinery

• Creality Ender-3 V2 Neo 3D Printer 220x220x250mm
• Sewing machine Singer Heavy Duty 4411

Measuring Equipment

• NDi KC-280A Anemometer (measures air velocity)
• Micron Q1266 sound level meter (measures sound level)
• Uni-T UT373 laser tachometer (measures fan speed)

Step 1: 3D Printing the Parts

3D files can be downloaded from here: https://www.thingiverse.com/thing:5870488

All parts ideally require 0.2mm layer height, 100% infill, and use either PETG or ABS filament for strong, durable and long lasting parts.

Print times are as follows for a Creality Ender-3 V2 Neo 3D Printer:

• Housing: ~15 hours (requires supports preferably only touching the build plate)
• Lid: ~7.5 hours (requires support)
• Fan Funnel: ~45 min (requires support) (best printed on its side)
• Inlet Filter Ring: ~25 min (no supports)
• Inlet Filter Cap: ~45min (requires support)
• Outlet Filter Base: ~50 min (requires support)
• Outlet Filter Cap: ~1hr 20 min (requires support) (best printed upside down)

Step 2: Adding the Electronics

The above circuit diagram directly corresponds with the layout of the components so that you can easily place, connect and test the relevant electronics in the housing. The red wires represent positive connections and the black wires represent negative/ground connections. This is important as some components only allow current to travel through them in a certain direction.

The next 5 steps will go into detail for adding these components. If it is your first time soldering, this 'How to solder' video is quite helpful.

Step 3: Preparing the Power-on Indicator Light

1. Place the PWM controller onto the right side of the housing.
2. Measure out an appropriate length of black & red wires from the PWM controller to the power-on green LED hole (roughly 40mm).
3. Solder these wires to the green LED appropriately.
4. Desolder the existing red LED on the PWM board and replace it with the connection to the green LED (ensure that the negative and positive connections are correct!).
5. Check the LED reaches and slots into the hole from the PWM controller.

Step 4: Preparing the Fan Control Circuit

1. Slot the fan funnel adaptor into its hole in the front center of the housing.
2. Place the blower fan with the outlet connected to the fan funnel.
3. Measure out an appropriate length of the blower fan wires to reach the PWM controller. 
4. Strip the wires and screw the wires into the appropriate motor terminals on the board.
5. Attach the potentiometer switch wires to the PWM controller.
6. Reduce the length of the cable between the pot switch and the PWM controller leaving enough length for the pot switch to reach the lid pot hole with excess for when taking on and off the lid.

Step 5: Preparing the Power-off Warning Circuit

1. Using the circuit diagram, solder the necessary components onto the relay using the least amount of cable as possible.
2. Start by soldering the diode and capacitor straight onto the appropriate terminals of the relay. Then solder the buzzer wires and LED wires (ensure that the negative and positive connections are correct!). Try to solder the components so that they can lie flat onto the housing.
3. Slot the red LED into the hole on the left side of the housing.

Note: The buzzer is quite loud / high pitch with the intention to overcome loud background noises. Feel free to remove the buzzer if you just want the power-off LED to flash when the power is disconnected.

Step 6: Wiring Up the Power Connections

1. Solder the grey/black wire onto the USB A connector with the black-striped wire connected to the GND terminal and the white-striped wire connected to the VCC terminal.
2. Cover this with the black casing which should snap nicely together.
3. Thread the other end of the USB power cable into the hole on the left side of the housing.
4. Then split the wires into two. One goes to the power-off warning circuit and the other goes to the step-up voltage regulator (see the PAPR circuit diagram in step 2). Ensure that the negative (GND) and positive (VCC) connections are correct!
5. Then connect the output of the step-up voltage regulator to the input power of the PWM controller.
6. Test all the components work by plugging in the USB A connector into a 5V 2.1A power bank to check the following:
7. As the fan speed increases, the green LED brightness should increase based on the pot rotation. When the pot switch is off, the fan and green LED should be off.
8. The red LED should flash and the buzzer should make a sound when the power is disconnected.
9. Stick all the components down onto the housing with a hot glue gun.

Step 7: Adding the Lid

1. Push the pot switch into the lid pot hole and add the pot knob on top. You might need to use hot glue to hold the pot switch in place under the lid.
2. Slot the lid onto the housing by pushing it in with the front making contact first (2.1) then pressing the back down until it snaps shut (2.2).

Step 8: Adding the Inlet Filter

1. Cut a circular piece of the non-woven spun bond polypropylene pre-filter material to the same size as the inlet ring (57.5mm diameter).
2. Cut a circular piece of the HEPA 13 filter also to the same size as the inlet ring (57.5mm diameter).
3. Stick the pre-filter to the bottom of the ring and the HEPA filter to the top of the ring using a non toxic glue stick. Allow the glue to dry.
4. Place this ring on top of the lid inlet hole and then use the inlet cap to snap the ring in place.

Step 9: Attaching the Forehead Foam Support

1. Cut a piece of foam with a sticky back to a size of around 20mm x 30mm x 200mm. Some face shields come with their own foam which can be used.
2. Stick the foam to the back of the housing making sure it is stuck down properly with an even amount on each side. Use superglue if necessary otherwise use polyethylene foam tape to adhere to the housing for ease of replacement.

Step 10: Attaching the Head Strap

1. Cut the elastic strap to a desired length to go around the back of your head (~350mm).
2. Cut another elastic strap to a desired length to go around the top of your head (~230mm).
3. Punch out two 5mm diameter holes leaving a 20mm gap in between the holes at one end of the longer strap. Do the same on the other end. Cut a curve around the corners for aesthetics.
4. Punch out one 5mm diameter hole on either end of the second shorter strap and cut around the corners.
5. Attach one end of the longer strap to the two connection posts on the left side of the housing and then do the same for the other end on the right side of the housing.
6. Attach the ends of the shorter strap on top of the longer strap to the posts which are slightly higher up.

Step 11: Preparing the Visor

1. Cut the visor to size based on the template provided. Some visors come with protective film so make sure to peel this off.
2. Punch 5 holes with a diameter of 3mm at the top of the shield at the specified points.
3. Attach the visor onto the housing to check all fits nicely. Make sure to push the visor holes fully into the spokes and tuck the sides of the visor into the support flaps of the housing.

Step 12: Sketching and Cutting the Hood Template

There are two ways to do this.

1. Print the template out to actual size (9x A4), cut the template, trace the template onto the Tyvek, then cut it out.
2. Draw the template straight onto the Tyvek using the measurements provided and then cut it out.

The template is provided below. Ensure that you are drawing on the rough side of the Tyvek material; this is the side that you can see fibre strands showing through.

Step 13: Sketching and Cutting Slits for the Folds

1. Measure and mark 20mm from all the borders except the top border, left border and right border. See the hood fold template provided below.
2. Cut slits around the arches up until the marked offset.
3. Fold over the border at the dot-dashed line shown in the hood fold template below.

Step 14: Adding the Arch Supports and Taping the Folded Border

1. Cut out separate pieces of Tyvek for arch supports. Use the arch support template provided below.
2. Place them around the arches underneath the cut folded slits. Then sticky tape the folded slits down onto the arch supports. This provides better strength around the arches and makes it easier to thread through the elastic without it getting caught.
3. Seal the rest of the border with sticky tape to create a channel for the elastic to go through (tape shown in blue).

Step 15: Attaching the Visor to the Hood

1. Stick down the visor sides and bottom in the center of the hood using double sided tape onto the smooth side of the Tyvek material which is unmarked. Ensure to leave a 20mm offset from the center visor window and leave the top of the visor open.

Step 16: Stitching the Visor and Hood Border

1. A heavy duty sewing machine should be used to handle both the plastic visor and Tyvek material.
2. Setup the sewing machine to have a stitch width of 0mm, stitch length of 2.5mm, and set to simple continuous stitch. Use white polyester thread.
3. Stitch the folded borders down with a sewing machine.
4. Also stitch the visor sides and lower border down onto the Tyvek.

Step 17: Threading Through the Elastic

1. Make an access hole in the center of the lower border channel for the elastic to be attached to a toggle.
2. Thread the thin elastic (6mm width) through the border channel starting from the right side of the border all the way to the center access hole. Once the center is reached, thread the elastic through the toggle and back into the border channel.
3. Continue to thread the elastic through to the other side.

Step 18: Adding the Outlet Filter

1. Cut the face mask into a circle with a diameter of 50mm.
2. Stitch around the circumference to keep all layers intact.
3. Punch a 2mm hole in the centre.
4. Seat the filter on the outlet base and pass the base through the outlet hole of the hood.
5. Snap on top the outlet cap to secure the filter in place.

Step 19: Stitching the Sides and Top Together

1. Bring together the left and right side to form the back of the hood. Ensure the visor is on the inside of the fold.
2. Stitch the sides together as well as the top border.

Step 20: Bundling the Top and Turning the Hood Inside Out

1. Bundle the top of the hood and secure with a few staples.
2. Turn the hood inside out carefully so that the visor is now on the outside of the hood and the bundle is on the inside. No markings should be visible on the outside.

Step 21: Attaching the Hood and Visor to the Housing

1. Stick double sided tape onto the back of the lid.
2. Attach the visor holes to the housing spokes. Make sure to push the visor holes fully into the spokes and tuck the sides of the visor into the support flaps of the housing.
3. Stick down the Tyvek hood onto the double sided tape on the lid.

Step 22: All Done

The device is ready to use!

Simply plug the device into a 5V 2.1A power bank to be kept in a pocket, put on the hood with the headband around and on top of your head for support, adjust the toggles to tighten or loosen the elastic and finally turn on the device by rotating the potentiometer to a desired airflow.