Over the last several months, I have spent a lot of time researching methods of sterilization for many different things like food and its packaging, money, and being able to re-use personal protective equipment. While bathing most things in bleach or rubbing alcohol seems to be the most common solution, chemicals just aren't feasible for all situations. I ended up choosing between two available options; Ultra Violet Light (UVG with Ozone) and steam/moist heat.

This is going to show you the steps I went through to create my own portable steam sterilization chamber.

Please note, I had a handful of disposable respirator face masks from when I acid washed my swimming pool last year, and these have become something I take great care with. Recently, the CDC released information regarding the Decontamination and Reuse of Filtering Facepiece Respirators that included these test results:

Moist heat incubation

Duration: 15–30 min

Temperature: 140°- 149°F (60°- 65°C)

Relative humidity (RH): 80-85%

Filtration and fit performance: pass with minimal degradation

Tested virus reduction: minimum of 99.99%

This was one of the deciding factors to try this, and cleaning PPE is where the sterilization chamber gets used the most. I have to say I am extremely satisfied with the results so far.

Speed - relatively fast, not requiring hours of drying in the sun or sitting under a UV lamp
Shape - Items come out crisp and clean, looking almost new, no wrinkles or warped edges
Function - The elastic is still elastic, something I have found quickly degrades when repeatedly submerged in bleach and rinsed
Ease of Use - no bad lingering odors, barely noticeable dampness, can be used right out of the box

Supplies

Steam Machine
Styrofoam Cooler
Aluminum Foil
Aluminum Tape
Pipe Insulator Tube
Wire shelf
Timer and Thermometer (for monitoring)

Step 1: The Chamber

The whole idea for this project started when I came across an old styrofoam cooler with one of the corners of the lid broken off. I figured the insulated box would contain the steam enough to keep anyone using it protected from burns and allow it to reach the desired temperatures. As an added bonus, I made a new grasshopper friend!

Step 2: Inside the Box

To minimize the possibility of melting the styrofoam but still benefit from its insulative properties, I lined the inside with aluminum foil and used aluminum tape to adhere the pieces to the sides and top. I made sure to leave the connecting edge clear where the lid set into the box so there would be no problem fitting and sealing the lid.

Step 3: Where to Place the Items?

Because there would likely be some water pooled at the bottom, I needed some kind of platform to elevate the items to be cleaned. It must also allow the air/steam to flow freely around the entire object.

I ended up going with an old plastic-coated wire shelf I found in a junk fridge (which I have turned into a composter, but that is another story for another day!). This was also covered using the aluminum tape.

** Note: My initial thought was to invert the shelf to hang from the lid so it would be raised and lowered when opening and closing the box. This would allow me to clip things to hang under it as well as use it as a shelf. Unfortunately, it was too heavy for the tape and just pulled the foil from the lid. I ended up just setting it in the box, but I still like the idea of it hanging from the lid so I will keep trying to think of new ways to attach it.

Step 4: Introducing the Steam Element

The steam from my cleaner would enter the chamber through the gap where the corner of the lid had been broken off.

This was accomplished by removing a small piece of the corner and melting the Styrofoam to create a smooth circular hole.

I completed this task outside with a protective face mask by heating up an old spoon so there was only low heat directly applied to the edge. I cut a section from a plumbing insulation tube, which was a more flexible material that would allow for adjustments in order to fit the hole and minimize the amount of steam that could vent.

** Melting Styrofoam creates toxic fumes and should only be done with extreme caution and adequate ventilation,

Step 5: Testing - Time to Sterilize

All that remained was to make sure the minimum requirements were met and the system was functional, then it would be ready to start my test run.

Even though I had no method to test relative humidity, I knew a mostly enclosed chamber would limit the venting of excess steam through the entry hole. The relative humidity would quickly rise and hold at close to 100% due to being contained, similar to how a steam room works.

Next was being able to provide consistent steam for a minimum of 15 minutes while maintaining a chamber internal temperature over 140°F (60°C). The steam cleaner I have is very basic, so instead of trying to hold the handle to keep it running for that long, I used a conduit clamp to squeeze the handle (definitely not recommended in the user manual) and the timer on my phone. If I had to go out and buy one for this project, I would spring for some additional features like a timer, and automated shut-off.

Finally, I stuck a meat thermometer through the hole with the end away from the edge so I could monitor the temperature for the duration. After turning on the steam, the temperature quickly rose, maxing out at just below 215°F (101°C) and averaging 200°F (93°C).

I was very pleased with the results. After having to use ragged masks that start to smell of chemicals and a hint of moldy dampness, I love now clean they smell and how the moisture does not remain, leaving the dry enough that they are ready to use immediately.

I hope you enjoyed and maybe got some interesting ideas!