UPDATE: previous version of this device did not include an enclosure for the PSU. Those files are now attached, along with photos of the entire device in use. The coronapile is held togeher with 6-32 threaded rod and nylock nuts. The PSU enclosure is held together with M3 X 20 mm screws. This project assumes a moderate level of electronics assembly competence, and is intended for the intrepid DIY'er or as the beginning of a discussion on simplifying the assembly (e.g. by having the PSU board mass-produced).

A small, homebuilt ozone generator that can be worn in a fanny pack or backpack for the purpose of disinfecting an N95 mask before re-use. In environments where providers are re-using disposable PPE, this could allow a person to reduce their risk without the need for centralizing a process. Each provider keeps one of their N95 masks (or other small PPE item) in a resealable plastic bag, where an ozone generator runs to produce high concentrations (1000's ppm) of ozone. The user determines the dwell time using an external timer (e.g. phone, watch, etc.). The small amount of testing I have done indicates that the device can create several 1000's of ppm O3 from room air in a few minutes inside a sealed 1 gallon ziplock bag (filling the bag with medical oxygen before running would produce much higher concentrations), on a power consumption of about 3W. The device can be powered over a USB cable from a common, off-the-shelf back up battery for hours of use. Using a 1 gallon ziplock (or equivalent), the typical cycle might consist of sealing the PPE in the bag, running the device for 5 min, then wait 20 min (half-life of O3), then cycling again for 3 min, wait 20 min, repeat once more, then move to a well-ventilated area, and remove the N95 mask. Users would need to be careful not to breathe high concentrations of ozone, either retained in the mask, or from the sanitizing device itself. I started from the documentation produced by this person: http://www.bigclive.com/oz.htm. It would probably be easier to have the high voltage PSU mass produced than to include directions for hacking the cold cathode tube PSU (which is already well documented in bigclive's post, linked here).

The design uses a lightly-hacked inverter power supply sold for powering cold cathode tube lamps, glass microscope slides, a 40 mm fan, and copper slug tape. I created a coronapile of 6 corona plates (each with four lines of corona the length of the plate, and added a Pololu 5V to 12VDC boost converter, and a micro USB jack, so that it can be powered by 5VDC over a USB cable; and 3D printed housings. I am still working on the 3D printed housing for the power supply, and I would like to automate the timing of the cycle with commonly available discretes (e.g. 555, etc.). With enough interest, I or someone else could design scratch-built power supplies that could be assembled from kits, rather than hacking the cold cathode tube PSU's. The parts used to construct my prototype cost about 16USD.

Data on sanitizing with ozone are widely available. The goal of this project would be to reduce risk, not eliminate it. It's fair to say that a device like this would not sterilize an object. The efficacy of the device could be tested in a lab setting, but if my O3 concentration results can be corroborated, kill-rate/concentration/dwell time data from others could be used to justify its use.

CAUTION: OZONE IS TOXIC. Do not open the device unless you are in a well-ventilated (preferrably outdoor) area. Be sure to air-out items sanitized by the device prior to use.