In another thread, I mentioned using an ozone box to sanitize my groceries and clothing after a trip into town and a couple folks were curious about how to do that. Here is some food for thought. 1. I did a bunch of google searches to try and find out just how much and how long is needed for ozone, which is a strong oxidizer, to solidly kill the virus on surfaces. In short, atmospheres with 20-35 parts per million (ppm) for 30-70 min or 100 ppm for 10-15 mins seemed to be the magic doses. I didn’t find published data about ozone killing covid-19 specifically but there is ample data that ozone kills the SARS virus, a type of corona, and other similar viruses and many authors were confident its good killing covid. Here is a link to some of that info: CA2602230A1 - Apparatus and method for using ozone as a disinfectant - Google Patents 2. How to generate O3. There are plenty of ozone generators on Amazon and eBay. Avoid those sold through multi-level marketing entities as those tend to be ridiculously more expensive. Here are 2 that I have: Big one: https://www.amazon.com/gp/aw/d/B07WSSY8YK Small one: https://www.amazon.com/gp/aw/d/B07CTW9XPY I note the prices on these have gone up a bunch in the last few weeks. The big one has gone up from about $55 to $82 and the small has gone up about $7-8. 3. To get sufficient concentrations you need to constrain the volume, too big of a space and/or too small of generator and you will have trouble getting to 100 ppm. I just used a couple cardboard boxes. There is some math to figure out the concentrations for different size boxes and different sized O3 generators. We need the volume, V (in cubic meters) of our box. You can measure it in feet, inches, whatever and then use an unit converter to get cubic meters. (Cubic feet x .0283 = cubic meters) 4. Next we need the ozone production rating for the generator. We’ll call that GR and we’ll specify that it must be in milligrams per hour (mg/hr). All of units I’ve seen are spec’d as mg/hr. The big one above puts out 5000 milligrams per hour and the little one is 80 milligrams per hour. 5. BTW, we do use the mass of air in the calculations but it is already figured into the equation below. At 20 degC and “standard pressure” air is about 1.2 kg per 1 cubic meter. 6. Now we can calculate the concentration, C, in ppm, after some duration of time, T measured in minutes. 7. So the equation becomes C = T * GR/(72*V) Example: Assume we have a box 2 ft x 4 ft x 4 ft. That is 32 cubic ft that converts to .906 cubic meters. If our generator is 5000 mg/hr then we have the following: C = T * 5000/(72 * 0.906) C = T * 76.6 So after T = 1 minutes the concentration is 77 ppm. After 5 mins we are at 383 ppm. Procedure: So, I spread stuff out on racks in the big box with the generator and small fan and shut it up. I let the generator run for 3-4 minutes to be sure we are well above 100 ppm and then let the box sit there with the circulation fan running for another 10 minutes or so. Open box, let it air out for 10-15 minutes then empty the stuff. Clothing I let air outside for a couple hours to let the odor dissipate. Warnings: O3 is toxic. 50 ppm for 30 min can be fatal. Much lower doses can irritate your eyes and mucus membranes. I do all this outside on my screened in porch. You don’t need a gas mask, etc., just don’t stick your head in the box and avoid breathing this. Parting comments: Currently I am trusting the generator ratings provided by the manufacturers as I have little choice. I am still awaiting an O3 sensor I ordered several weeks ago so I can actually measure concentrations. You will note that in the procedure above I actually get theoretically above 200 ppm in the example. That’s because I don’t yet trust the generator is really 5000 mg/hr and I go double to be safe until I can measure it. I do ask the other science minded folks here to please double check my numbers and equation. It’s easy to drop a decimal place or two in these. I use the small O3 generator with a small box. It is battery operated and puts out only 80 mg/hr when plugged in and 20 mg/hr running on the internal battery. In the box for a case of long neck beer, it gets above 100ppm in 4 minutes @80 mg/hr and in 15 min @ 20 mg/hr. We mostly use it on the front porch and toss the mail in it. 25 min later we can read our mail. Lastly, to make all this real easy, I will probably stop using the big box. The pickup truck has a cap on the bed so next time (provided I have my sensor to confirm concentrations) we will just load all our groceries in the truck bed at the store. When home toss the clothes in the back also, stick the generator and a fan in the back, close it up and 20 minutes later its all sanitized. Stay safe. AT
@Airtime - Thanks for the post. You can get test strips while you're waiting for the meter at the link below for just under $21. https://www.amazon.com/gp/product/B00S1UPL96/?tag=survivalmonke-20
Thank you for the suggestion. I had seen those. Unfortunately the top reading range is greater than 210 micrograms/cubic meter which correlates to only 0.105 ppm and we need to read up to 100 ppm. We could possibly do some constant volume sampling and controlled dilution but my sensor is suppose to be delivered next Wednesday, we’ll see. Not holding my breath. I appreciate your efforts to find a solution. Thanks. AT
