Introduction: DIY PPE for COVID-19 Infection Avoidance
Hello everyone! This project is actually a kind of "Pre-exposure prophylaxis (PrEP)"; as breathing you own filtered air might help you avoid getting COVID-19. It provides one way to avoid breathing the contaminated air all around us, when we are in social situations. It uses items readily available on ebay - but not necessarily intended for medical PPE use. I bought all of the parts there for my own HEPA filtered, forced air fed PrEP, PAPR hood system for well under $100. The most difficult to get is the PAPR hood part - it's now expensive. However I'm sure there's a sister project here or elsewhere for constructing one yourself. This Instructable is for the filtered airflow pump component.
The project is a dirt simple, cement half A to half B effort - yet yields what I believe to be an effective ppe for use in socialized environments; grocery shopping, commuting using public transportation; basically attending any event that puts oneself in close-contact with others while in an enclosed space. The utilitarian pump/filter/battery arrangement can be harnessed to an ordinary pant belt and worn similar to a "fanny pack"...
A single 3.7V (nominal) lithium cell powers the popular inflation pump sufficiently. As I do not have access to an airflow measurement system, what I claim to be a usable airflow rate was only determined empirically. I'm a 63 year old, capable of jogging a couple miles, so my fresh airflow breathing requirements I assume are average.
I'm able to stay in the hood for over an hour, breathing comfortably, while doing light work, on just one SAMSUNG--18650-26J cell - taking it down to from fully charged to 3.5V in that time. (Discharge cutoff by spec is 2.75V) Just one cell is apparently sufficient for grocery shopping, even with the luxury of taking your time as you go through selecting items in the store! To ensure my continued safety, I do carry a spare...
Social acceptance in a few shopping trips using the apparatus seems fine. Most are simply curious, some present a thumbs up or take my picture to show friends. No one seems scared or offended and store employees engage me in light conversation.
Variations can of course include a mask based interface to nose and mouth, as I assume one could connect the completed machine part to any face-sealed breathing apparatus headgear. However over the past few days I've seen the availability of professionally made, filtered face-mask respirators go down on ebay. I can only imagine in the ensuing weeks, such devices will be unobtanium.
Any help, suggestions, comments welcome. I only ask that we please keep them constructive - I realize this is live internet participation and therefore expect some criticisms.
Potential Hood structure; https://www.ebay.com/itm/Bullard-RT-Series-Respirator-RT1-Tychem-QC-Hood-Only-FREE-SHIPPING/353038935237
Battery holder; https://www.ebay.com/itm/18650-Battery-Holder-3-7V-Case-Storage-1x-2x-3x-4x-18650-Battery-Box-Wire-Lead/264447437635
Air pump; https://www.ebay.com/itm/DC-12V-Car-Auto-Electric-Air-Pump-Inflator-3-Nozzles-for-Air-Bed-Mattress-Boat/222546775709
Connecting Hose; https://www.ebay.com/itm/Everbilt-Universal-Corrugated-Dishwasher-Drain-Hose-Kit-6-Feet/202774831121
Step 1: Apply Glue to Filter Cartridge
Using the recommended glue or equivalent, place a large bead - about the width of a stick pen - around the bottom of the filter, just outside of the black foam gasket.
Step 2: Connect Filter Cartridge to Pump Housing
Press the glue loaded filter bottom symmetrically about the pump motor intake tube, such that a clean seal is obtained all around the periphery of the filter bottom to the pump impeller housing. Preference; there's a plastic screen to prevent inhalation of foreign objects; you may choose to first break this out as with the filter in place, this wont be a problem.
Allow glue to dry overnight.
Step 3: Trim Dishwasher Discharge Hose to Length
Trim the dishwasher hose to an appx 24" length, initially measured from the larger of the two end connectors. Use the one pump adapter end (provided with the pump) that fits snugly into the dishwasher hose and glue it in place at the freshly cut end. Allow glue to dry overnight. Note: length may vary, depending on the type of mask / hood you're connecting to -
Step 4: Attach Battery Holder
Glue the battery holder to the bottom side of the pump motor case. There are vents; be sure to cover these completely with glue, as who knows the efficacy of any seal between the motor housing and the impeller chamber. You only want filtered air to enter the hood or mask. You may put a layer of glue over the on/off switch - in the on position - to prevent any unfiltered leaks through that component. You may orient the batter holder so (+) is facing up, when the machine is worn (same side as pump exhaust port).
Allow glue to dry overnight.
Step 5: Connect Electrical Wires
Crimp-connect the battery holder wires to the DC power wires of the pump. On the pumps I specified, they use some bizarre metal formulation in the wire that doesn't lend itself very well to a soldered connection - my pictures show that I managed to do it, but barely - a crimp connect is the only good way. On my pump, the brown wire is (+) the blue (-).
Step 6: Test Basic Operation
Test the operation of the pump motor / battery connection using an 18650 cell. You may want to run it for a while, to evacuate any glue fumes from the assembly.
Step 7: Fabricate "Belt Hoops"
Fabricate a pair of rubber hoops or bands to allow the assembled machine to be connected to a belt, so it can be worn in a fanny-pack style - behind you for a PAPR hood, or in front of you for a mask.
Step 8: Test Flow in Hood / Mask
Connect the large end of the hose to the rear input port of your PAPR hood, secure using appropriate tie wraps or rubber bands. With the filter pump machine and hood in place on your person, practice connecting the hose end to the pump output behind your back and connecting / replacing the battery. Turn it on ASAP and note the cool filtered air coming into the hood.
Step 9: Further Test and Experience the Filtered Air System
Test the arrangement by wearing it for some time, being careful to note any stress occurring with your heart, lungs or an indication by getting a headache. It should be intuitively obvious that the use of this is a temporary measure, as the air quality within a hood over time will NOT be as good as breathing normally. Obviously keep it out of the reach of children when not in use.
Step 10: Ready to Roll!
Only after having mastered the experience of using the apparatus; connecting the hose, exchanging the battery, simply being constrained within the confined space of having a plastic hood over your head with the airflow and noise, you should now be ready to take it outside and into an enclosed space with other people present.