20 Mar COVID-19 Advice by Dr. Hon: Reusing Masks by Home Sanitization
Posted at 08:50h in Blog
by Dr. David T. Hon, founder and CEO of DAHON folding bikes
Masks are expensive and in short supply. Reusable ones would be desirable. But it is generally believed that water-based sanitizers like alcohol would compromise the porosity and effectiveness of the melt-blown fabrics in most masks.
I want to suggest here that proper Pasteurization (1) using some home appliances can inactivate all COVID-19 coronavirus in any mask models. Invented in the 19th century originally for wine, pasteurization is now widely used for sanitation in many fields, including laundry dryers for clothes (2). All germs and viruses are killed when properly pasteurized, according to published documents.
Including COVID-19 as well?
“Yes”. COVID-19 is just a new form of coronavirus, which, as a class, has been causing diseases for at least as long as pasteurization. According to the (U.S.) National Milk Producers Federation (NMPF) in March 2020, pasteurized milk is free of COVID-19 (3).
More specifically, viruses and bacteria thrive at low temperatures and quickly die at higher temperatures. (That is why humans go into high fever for days as a last resort against diseases when the immune system has failed; SARS fizzled out in the summer). Pasteurization can in principle occur at temperatures as low as 50°C – if one waits for a couple of hours. The higher the temperature, though, the shorter would be the pasteurization time. For foodstuffs, the temperature is often 72°C for only 15 seconds in mass production. Table 1 provides the temperature vs. time required in pasteurization (4). We can pasteurize masks for longer times for safety margins.
Laundry dryers typically run between 55 to 65° C at maximum settings. Some run higher. Unless you know the exact temperature and apply the above table 1, it is safe to set the dryer at maximum temperature for one hour. Masks will come out completely sanitized and smelling fresh as new, ready for another day!
Kitchen ovens can also work, but many do not go below 80°. Above that, many mask materials will be damaged. Ovens with temperatures below 80° are available if you search online.
A hairdryer is certainly hot enough to kill viruses, but runs the risk of overheating and destroying the mask as well. (I am designing a simple device to regulate a hairdryer’s temperature experienced by the masks. I will describe this inexpensive DIY contraption at a later time.)
UV light, used in many commercial and domestic sanitizing cabinets, is effective against viruses and bacteria. Check the manual for required timing. However, unlike heat, limited penetration in some units may limit the number of masks treatable at a time. Some advanced laundry dryers also use UV light along with heat.
The common microwave oven, unfortunately, will not work, as viruses are too minute for the electromagnetic wavelengths.
I hope citizens will save time and money, as well as exposure, by renewing masks at home to protect themselves and others. Hospitals and other institutions may also consider this practical proposition. Some public agency should undertake direct verification for a high return-on-investment!
I welcome suggestions and questions by readers or audience.
The author, Dr. David T. Hon, is a graduate of DBS, UC Berkeley and UCLA/USC (Material Physics), and a Governor of Amcham South China since 2001; he has over 350 patents in several fields.
“…by Louis Pasteur in the 1880s…”
2. Pasteurization by Laundry Dryers https://books.google.com/books?id=3yc632rlia0C&pg=PA594-IA3&lpg=PA594-IA3&dq=pasteurization+by+laundry+dryers&source=bl&ots=lylrS1InI8&sig=ACfU3U2FdNEyH_nCfuaJW39J2D9ryOA-lQ&hl=en&sa=X&ved=2ahUKEwjzsZKf4K3oAhXTP3AKHbTNCNY4ChDoATAGegQICBAB