Resources are scarce, so should masks be reused?

Resources are scarce, so should masks be reused?

Many people have asked whether it is okay to spray masks with alcohol. The reason I do not recommend is that it will affect the filtration efficiency. Recently, the news has updated risk of disinfection with alcohol: the volatilization of alcohol may take away the water in the mask, thereby removing the virus contained in it. If it is peeled off, there is a risk of inhalation the next time it is used.

Masks have become very scarce protective equipment during this period. The supply of doctors in the epidemic area is still insufficient, and the masks available to ordinary people are very limited. According to estimates, the current shortage of masks may be difficult to solve in the short term, and even affect the company's Time to resume work.

Therefore, under the premise of ensuring safety and effectiveness, the repeated use of masks is very important. Proper operation can greatly extend our safe use time. Safer and more economical use is more meaningful than blind search and hoarding.


First of all, we need to understand how long the mask can be used under normal conditions:

Medical-surgical mask:

The official opinion is 2-4 hours
Considering the scarcity of masks in the later period, the doctor’s recommendation is to extend it to 6-8 hours, and it can be extended appropriately if the mask is not damaged or contaminated and the nose strip is still usable.

N95 masks: based on a study of medical protective masks
The relationship between the filtration efficiency of N95 masks and the use time is as follows:

N95 Masks test

Note: The time (d) in the table is calculated based on 8 hours a day. It can be seen that after three days of use (24 hours in total), the filtration efficiency is about 94.7%, which still meets the requirements of European standard EN149:2001-FFP2.
Therefore, for ordinary people, it is certainly possible to wear it for 24 hours. After an additional 24 hours, the filtration efficiency can still reach more than 90%, and the filtration efficiency of the new medical-surgical mask is only 30%+.

After understanding the effective use time of masks, the next thing to be solved is how to safely and effectively use masks repeatedly during this time. This includes two aspects:

1. The safe use of masks: I won’t go into details here. There are already many popular sciences on the Internet. Here I think there is an article worth mentioning, which emphasizes that "only wearing masks + good hand hygiene" at the same time will be effective. Otherwise, it will be counterproductive. "For example, many people don't wash their hands before wearing a mask. The mask is already contaminated by their hands before wearing it.
I don’t feel comfortable after wearing it. I always touch the outside of the mask with my hands. I don’t wash my hands after removing the mask. The virus collected on the mask spreads to my hands. I touch the phone or other places with my hands, such as the doorknob of the house. A source of pollution. "

2. Mask disinfection: Regarding the mask disinfection plan, there are two factors to consider: the disinfection effect and the impact on the filterability of the mask. What we need is to find the premise that the virus can be eliminated to minimize the loss of filtration efficiency. After checking, The four currently feasible disinfection schemes are:

High-temperature cooking
Alcohol spray
Heat drying
Ultraviolet rays

According to the results of a number of studies and experimental tests, among the four options, high-temperature cooking and alcohol spraying have a relatively large impact on filtration efficiency (about 10-30% reduction). The least impact on filtration efficiency is thermal drying and ultraviolet rays. After these two treatments, the filtration efficiency can still be maintained at at least 90%. But for our ordinary households, considering the availability of equipment and the convenience of operation, I think ultraviolet rays are better than thermal drying because most households do not have an oven and it is not easy to buy and install an oven. Even if there is an oven, every time Drying at 60-70 degrees for more than 30 minutes is also prone to secondary pollution. In contrast, ultraviolet disinfection equipment is easier to obtain, and the operation and time are much more convenient.


Resources are scarce, so should masks be reused? - Safeagle

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