Introduction: Clean Mask Project
In this Instructable you will learn how to make a UV-C Sanitizing Box
for N95 respirators. This item is intended for use by medical professionals and first responders during the COVID-19 pandemic. This UV-C Sanitizer will help stretch the supply of N95 respirators until supply catches up with demand. This sanitizing box is intended for emergency use only.
Step 1: Supplies
The supplies are procured from Home Depot, Harbor Freight Tools, and Petsmart or Petco.
Some substitutions may be a better fit for your tools or resources. When substituting parts keep the following in mind: 1. The sanitizer box must be fully enclosed when in operation to reduce airflow and prohibit direct visual observation. 2 The lamps must be positioned approximately 0.25" from the top and bottom of a standard N95 respirator for maximum efficiency. 3. The resulting product should be simple enough that a maintenance person at a hospital can assist with troubleshooting should problems arise (no complex circuitry or custom fabricated parts). Keep it as off the shelf as possible.
- Harbor Freight Tools
- 21" Voyager Tool Box - 25.99
- Power strip - 4 outlet - 3.99
- Self tapping screw assortment - 9.49
- Magnetic Hook Set 4 Pc. - 3.99
- Momentary Power Foot Switch Item # 96619 - 13.99 - Item 96619 is not the same as 96618. The momentary (press and hold to keep on) is what you want.
- Home Depot
- Double sided tape - Extreme Mounting Tape - Scotch - 7.98
- Zip ties 8" Mounting Tie - Commercial Electric - 9.98
- 15 Amp 125-volt Flanged Inlet - White - Leviton - 10.97
- #10-32 x 1/2 in. Combo Round Head Zinc Plated Machine Screw (8-Pack) - Everbilt - 1.18
- Multi-Purpose Foil Tape (Aluminum) - Nashua - 7.88
- Nylon lock nuts 1/4-20 3 pack Stainless Steel - Everbilt 1.18
- Threaded rod 1/4-20 36" Stainless steel - Everbilt - 5.98
- Reflective Insulation Roll 24"x10' - Reflectix - 10.45
- Loctite Threadlocker Blue242 - Loctite - 6.47
- 2.3 ft. x 50 ft. Steel Rabbit Garden Fence Welded wire - Everbilt - 29.38
- Hole Saw 1 3/4" - Milwaukee - 15.97
- Security Bit Set - Dewalt - 5.97
- Any 1/2" board 8"x16" - plywood, wafer board or solid pine are all acceptable. I used scrap on hand.
- Petsmart or Petco
- TWO - Green Killing Machine 24 watt - 79.99-99.99 each Petsmart with curbside pickup applied a discount to get the 79.99 price.
- Tools you will need but probably already have
- 1/4" drill bit
- 3/16" drill bit
- 13/64" drill bit or #7 drill bit
- 1/4-20 tap and die - may be substituted with 1/4-20 tee nuts (3) and an appropriate drill bit
- Electrical outlet tester
- Electric drill
- Screwdriver set
- Tin snips
- Grinder, hacksaw or cutoff wheel
- Electrical tape
- Wire strippers
- The radiant barrier in stock at my Home Depot is the bubble radiant barrier. I used radiant barrier I had on hand from Amazon - Radiantguard. This type is thinner. Either will work.
- Nylon lock nuts and threaded rod may be substituted with 6" bolts or machine screws if available.
- The only security bit set available at Home Depot included a bit that was slightly too large for this application but worked for several boxes before I got impatient and broke it when moving too quickly. The necessary bit is the flat blade with the center removed. When I broke mine I used a diamond blade to remove the center of a smaller flat blade. This ended up working better than the Dewalt product.
- If making more than one sanitizer box the following items may provide enough supply for multiple boxes: self tapping screw set, double sided tape, zip ties, multi-purpose foil tape, threaded rod, reflective insulation, Loctite, Welded Wire Fence.
- An additional product I could not find at Home Depot or Harbor Freight was a short extension cord with a lighted end. These were available on Amazon. "Miady Short Power Extension Cord Outlet Saver, Female Plug with Light". A lighted end will allow the user to see when the lamps are energized without looking into the box (and damaging their eyes).
- Total cost $356.46 (with tax) if you have your own drill bits and tap/die. If you have access to scrap galvanized (or better yet - stainless steel) welded wire (16-gauge seems ideal) you can save a good deal of money as the project only requires an 8"x8" section.
Step 2: Drilling the Power Inlet Hole
Use the 1 3/4" hole saw to drill a hole near the bottom-center of the right side of the tool box.
I used a magnetic hook covered in radiant barrier to pick up the metal shavings after drilling the hole. Keep the inside of the sanitizer as clean as possible. It will be tightly filled when complete.
Step 3: Arrange Electronic Components
- Open the Green Killing Machine boxes and discard the water pump, elbow bracket and filter.
- Place the AC adapters on the left side of the box and double sticky tape them to the side of the box.
- Place the transformers on the right side of the box and double sticky tape them to the bottom of the box.
- Temporarily place the power strip in the upper middle of the box and measure where to cut the cord to attach it to the flanged power inlet.
- Cut the power strip and strip the wires.
- Pass the stripped wires through the hole to the outside of the box and attach them to the power inlet.
- Use an outlet tester to test the wires for proper placement.
- Use the self tapping screws to secure the power inlet to the box.
- Use double sticky tape (it takes two layers on the recessed portion) to secure the power strip to the upper middle of the box floor.
- Use the twist ties that were include with the lamps to clean up the cords and minimize clutter on the box floor. You may also use zip ties if necessary.
Step 4: Prepare the Lamps
- Remove the small black rubber pieces that cover the five security screws. I used a pick tool. Any small sharp point should work.
- Use the security bit to carefully (remember I broke mine after doing a few of these) to remove the five screws. Save one screw for later.
- Separate the halves of the housing. Be careful to not break the bulb.
- Cut the tip off of the side of the housing that attaches to the pump and filter. Keep enough of the tip to cover the end of the lamp. Screw the cut piece back in to the other side of the housing.
- Repeat this process for the second lamp.
- Zip tie around the glass of the upper lamp with mounts positioned on opposite sides of the lamp (one up, one down).
- Center the upper lamp in the box lid and mark the holes for the zip tie mounts.
- Use the 3/16" drill bit to drill the holes for the upper lamp.
- Test fit the upper lamp.
- Cut radiant barrier to insert between the box and the lamp and cut matching holes for the lamp mounts.
- Mount the upper lamp with radiant barrier behind it using the 10-32 machine screw/nut combo pack. Use Loctite to ensure that the nuts stay attached.
- Cut a 8"x16" piece of wood to be used as the adjustable floor for the lower lamp.
- Test fit the wood inside the box above the electronics. I used a small cardboard box to set the board on while I did this.
- Mark one hole on the left center of the board that will not interfere with the electronics below.
- Mark two holes on the upper and lower right that will not interfere with the electronics below.
- Drill the three marked holes with a 13/64" (or #7) drill bit.
- Tap the holes with the 1/4-20 tap.
- Wrap the board with radiant barrier (use aluminum tape to secure it) and cut out around the holes to ensure the threaded rod turns easily by hand in the next steps.
- Cut the threaded rod to 6" sections and clean up the threads with a die if necessary. Grind the ends smooth as the will be turned by hand for adjustment in the field.
- Place a nylon lock nut at the top of each of the three 6" threaded rods to allow easier manual manipulation.
- Thread the rods into the wood with the nylon lock nut on the top of the wood.
- Carefully pop the lower lamp out of the housing. Center the lower housing to the box, not the wood, and screw it down to the wood (two screws should do it). Place the lamp back in the housing.
- Use aluminum tape to wrap both ends of the housing of the upper and lower lamps. Pay careful attention to the base side of the lamps as there is no screw on that side. The tape will hold the halves together.
- Use aluminum tape around the upper radiant barrier to secure the ends and maximize reflective surface.
- Tape pieces of radiant barrier to the left and right sides of the box to cover the open areas. Do not tape these pieces to the wooden platform, they should hang over the platform. The platform must be able to be adjusted without cutting and retaping. Small slits will need to be cut to allow the lamp cords to pass through the right side.
- Wrap the lamp cords in aluminum tape to prevent UV damage.
- When all the radiant barrier pieces are sized and appropriately taped, lift the platform out enough to connect the lamps to their transformers. Ensure the power strip is in the on position before connecting the lamps. Ensure the AC adapters are connected to the transformers.
Step 5: The Grilles
- Cut an 8"x8" section of the galvanized garden fence from the 4"x1" section to make a grille.
- Flatten the grille as much as possible by placing it on a flat surface and using the edge of the flat surface to bend and straighten where necessary.
- Place the magnetic hooks on top/bottom of the box in pairs.
- Hang the grille from the hooks.
- Turn the hooks so that they provide tension/retention to the grille.
- Center the grille on the exposed portion of the lamps.
- Carefully measure (this can be tedious, like leveling a 3D printer) that the upper lamp (when in the closed position) is 2.5" from the grill surface and that the grille is 0.25" above the lower lamp.
- Use the adjustment bolts as necessary. Take your time.
Step 6: Foot Switch and Warning Label
- Connect the lighted plug (if you were able to get one) to the box.
- Connect the momentary foot switch to the lighted plug.
- Test the system to ensure that the lamps activate when the foot switch is depressed and deactivate when the switch is released. It is very important that you do not look directly at the lamps when they are activated. UV-C is extremely harmful to the eyes.
- Attach a warning label to the outside of the box to prevent users from operating in a dangerous manner.
Step 7: Cleanmaskproject.com
Go to cleanmaskproject.com to see research that supports and details the use of UV-C lamps to disinfect N95 respirators.
- The spacing of the lamps is key. At the dimensions noted on the previous page the mask will have a Log 6 reduction in virus (99.9999) in 20 seconds.
- As a matter of practice, the mask should be given a small turn after 10 seconds to eliminate any dark spots created by the grille.
- The straps should be cleaned with alcohol.
- Sanitized masks should be treated as if they are still dirty.
- Sanitized masks should only be reused by the initial wearer.