Mask Disinfection DIY - Ozone Zipper Bag

The outbreak of the coronavirus and mask shortage, led us in interest in how to disinfect masks. As of 4/1/2020, CDC has released guidance on the decontamination processes for reuse of N95 masks. This information can be found on the CDC website, But seem like those way are unable to accomplished at your home for daily usage. 

This is the fact, current mask shortage situation, We can't replace the mask everyday,how we can disinfection?

I did some research and list what I found and what is my solution, specially for Broad Airpro Mask.

Washing masks reduces their filtration effectiveness 21%. Skip;

Alcohol disinfection is not for mask,alcohol will remove the static charge in the microfibers in N95 facial masks, reducing filtration efficiency. tests found that dipping in rubbing alcohol reduced particle capture by 37%. Richard Juan show your the video; Skip;

Dry mask, Time is the killer! but how long need to wait? The CDC says that the coronavirus may remain viable for hours to even days. Skip.

Steaming the mask for 10 minutes or Placing mask in a low oven at 170°F for 30 minutes. These methods have been studied at Stanford but are not yet FDA approved.(Link) , you can try, but I will not, I am not  feel comfortable to bring the contaminate mask to kitchen and put it in the oven,it's place to cooking and eat. and Broad Airpro mask is the electrical device with battery, should not be heat up. It's option for N95 mask.

Ultraviolet light, A UV-C lamp is used to expose the contaminated FFRs to UV radiation for 15 minutes on each side of the mask (outer and inner). but when designing a procedure, must bear in mind that UV light is based on line-of-sight, and any part of the mask in shadow will not be disinfected. This maybe a option may not a best.

Ozone disinfection. This is my solution. Ozone is one of the most natural and powerful disinfectants. In contrast to UV radiation, ozone is a gas that could penetrate to every corners of container, thus it could disinfect more effectively. As ozone is unstable, it is readily converted back to oxygen, leaving no harmful residual ozone after disinfection. but federal government has not approved any ozone devices for use in occupied spaces, because ozone can cause health problems at high concentrations.get more information on  EPA Ozone Generators that are Sold as Air Cleaners.

Ok, Ozone is best for disinfection, let go ahead use it advantages and eliminate the negative effects.

1. What's the safety ozone concentration level.

The FDA requires ozone output of indoor medical devices to be no more than 0.05 ppm.

The OSHA requires that workers not be exposed to an average concentration of more than 0.10 ppm for 8 hours.

The NIOSH recommends an upper limit of 0.10 ppm, not to be exceeded at any time.

EPA’s National Ambient Air Quality Standard for ozone is a maximum 8 hour average outdoor concentration of 0.08 ppm

Ozone and Your Health Chart from EPA

So Ozone concentration less then 0.1 ppm in occupied spaces, we are safe.


2. What's the  effective Ozone concentration level for disinfection?

The concentration-time value (CT value, mg/L* min) is defined as the product of the concentration of the disinfectant (C) and the time (T) necessary to kill a certain type of bacteria at a specified killing rate. It shows that the smaller the CT value, the stronger the effect of the disinfectant.

Example, as below table, Ozone 0.02 mg/litter in one minute can attained 99% inactivation E.coil.

Hoff, J.C., Inactivation of Microbial Agents by Chemical Disinfectants

Table for Hoff, J.C., Inactivation of Microbial Agents by Chemical Disinfectants, EPA/600/2-86/067, 1986

Other data from Broad disinfection cabin catalog,

Ozone disinfection data

Date relevant articles, Disinfection Effect of Ozone Disinfectors found in CNKI.NET,sponsored by Tsinghua University

So the disinfection time can be 1 hour.

The date Unit converter:

1 mg/little = 1 ppm of Ozone in water (by mass) = 467 ppm of Ozone in air

1 ppm = 2.14 mg/m3 in air (by volume) = 0.06 mg/cubic ft

Base on the data, if need 5 ppm or more Ozone in the disinfection container and need 0.1 ppm or below in the room for breathe safety. It is means, On the some amount of Ozone, the room space should be minimum 50 time the disinfection container, if open the window for room ventilation will be even more safe.

I used 10 * 10 inches Ziploc zipper seal bag, it can be equated 1 Gallon volume(0.13 cubic ft), to keep the safe, the 50 gallon (6.68 cubic ft) space need for safety. have more space, the disinfection container size can be bigger.

I brought a tine 2mg/h ozone generator produce on Amazon. Link, I think this is the smallest one on market.

If place 2mg/h ozone generator on 2000 cubic ft room, it produce ozone 0.001 mg/cubic ft = 0.016 ppm per hour, Below the safe level 0.1; if you forget to shut off, it need 6.25 hour to reach 0.1 ppm, and the room can not absolutely sealed, the air leak will diluted the ozone concentration. I believe ozone will never can be over 0.1 ppm.

If place 2mg/h ozone generator on 1 Gallon bag, It can produce ozone 15.38 ppm per hour , It's good enough for disinfection. Put in your Broad Airpro Mask.

Bingo!  Enjoy. 

Don't let you face to close to the bag when open the zipper.

Ozone disinfection bag