A simple method for sterilizing N95 respirator & surgical masks.

Thanks for visiting the Simple Ozone Sterilizer (SOS) project. The SOS is a simple, easy to make, ozone sterilizer that could be a vital tool in fighting the COVID-19 virus. It could also be a simple sanitization method for other uses, deployable worldwide.

Low cost and deployable worldwide.

The idea for this sterilizer sprung up after hearing that healthcare workers were having to reuse fragile, disposable masks, and other types of non-reusable PPE (personal protective equipment). My wife is a healthcare worker, and I resell lab equipment and supplies. So, you could say I’m acutely aware that keeping non-reuseable PPE equipment clean and working order is no small task.

The design I came up with is one for a sterilizer you can put together fast. It’s relatively cheap, and just about anyone, anywhere in the world should be able to do it.

Facemask Sterilization Kit – Our Study

Ozone sterilization system for use by families and healthcare workers to disinfect facemasks for multiple reuses.


The current coronavirus pandemic has sparked global efforts to develop new and creative approaches in addressing shortages of personal protective equipment including respirator masks used by medical workers who treat COVID-19 patients and used by the public to reduce the spread of the virus within the community. While most currently available masks are intended for single-use only, safe and effective disinfection will allow these masks to be reused multiple times.

A portable system based on a non-destructive sterilization method was developed that consists of a small chamber producing ozone concentration levels reported in the scientific literature to deactivate almost all microorganisms. The system includes a small battery powered ozone generator placed inside the chamber.  Facemasks are loaded into the chamber and automatically exposed to an ozone concentration of 18 ppm for 30 minutes. The masks are then removed and ventilated in open air to allow residual ozone to degrade to oxygen.

System Design:

Facemask sterilization Kit
Facemask sterilization Kit

Ozone gas:

Ozone is a disinfectant known to kill bacteria and viruses upon contact. Ozone (O3) is an unstable gas that degrades back into its original stable state of O2 by forming a reactive free oxygen atom that oxidizes organic and inorganic compounds. Ozone gas can reach poorly accessible spaces that other methods such as exposure to hydrogen peroxide vapors, laser light or UV radiation cannot. Ozone does not produce harmful residues since residual ozone always converts back to oxygen within a few minutes.

System Performance:

The system generates an ozone concentration of 18 ppm within seven minutes of startup.

This concentration is maintained for thirty minutes, at which time the ozone generator

turns off automatically. The chamber performance is illustrated below.

Ozone concentration generated by chamber during 30-minute operation


To reduce excessive exposure to the ozone gas by a user, the O3 generator delays the production of ozone by one minute when the unit is turned on. This delay provides the user time to place the generator and the facemasks into the chamber without ozone exposure. The ozone generator turns off automatically after 30 minutes of operation

Ozone gas diffuses quickly into a room when the chamber lid is opened. To provide protection to room occupants, the volume of the container should be restricted to about 28 Liters.  For an ozone concentration of 18 ppm inside a 28-Liter chamber, the resulting ozone concentration in an average-sized room will be less than 0.01 ppm. This meets OSHA and EPA exposure limits.

Users of the sterilization system are advised to operate the system in well-ventilated spaces.


  • Ozone Generator Model S4Plus
  • Capacity: 30mg/h
  • Input Power: 5V DC, 1A

Project Team:

Uwe Reischl, Boise State University

John Schiff, Obtainium Science & Industry

Steven Rodoletz, Reuseum Educational, Inc.


The Contents provided are strictly for educational and academic research purposes and without any warranty or guarantee. The items that may be produced utilizing these Contents have not been tested for medical use. Reliance on the Contents for medical guidance or use of the contents in commerce is strictly prohibited. Boise State University will not be liable for any indirect, special, incidental, consequential or punitive loss or damages of any kind associated with the use of the Contents. Boise State University hereby disclaims any and all representations and warranties with respect the contents, including accuracy, fitness for use, errors, omissions, freedom from claims of infringement, and merchantability.


Put together your own PPE respirator mask sterilizer

First, a little background; I've been using a unique little device to ‘clean' my CPAP headgear and tubing. For about $50USD you can pick up a USB rechargeable ozone generator off of Amazon.

USB Rechargeable Ozone Generator.  Got it Amazon for about $50USD.
USB Rechargeable Ozone Generator

These generators are pretty powerful; they'll fill the entire room with that distinct ‘ozone smell' in 15 or 20 minutes. And if you're not aware already, ozone can be harmful to us, even at pretty low concentrations.

The Challenge:

The idea for this sterilizer arose after hearing healthcare workers were reusing fragile, N95 masks and other types of non-reusable PPE (personal protective equipment).

Things I thought were important:

Easy to assemble – no special tools or materials required.

Anyone could make one – this is REALLY important.

Deployable worldwide due to relatively cheap, realistically obtainable parts.

The Solution:

Simple Simple Ozone Generator Prototype
  • A plastic box with lid.
  • A battery-operated Ozone Sanitizer (I found this one on Amazon)

That’s right; this design is incredibly simple. It’s so simple it can’t work, right? Well, when in doubt find someone smarter than yourself and see what they think…   

Ozone easily reaches where other sterilization methods can’t.
You can put more than one mask in at a time.