Using a rice cooker to “dry steam” surgical masks for three minutes can have a sterilizing effect, an experiment by Chung Shan Medical University Department of Occupational Safety and Health associate professor Lai Chane-yu (賴全裕) and his team showed.
However, after dry steaming, the mask would have a lower filter efficiency compared with new masks, Lai said on Monday, adding that the method should only be considered if there is an insufficient supply of masks or they need to be reused in an emergency.
The team conducted several tests for cleaning N95 respirators, and found that a 70 percent alcohol solution, bleach, high-pressure sterilization and rice cooker were all effective sterilization methods, Lai said.
Dry steaming masks for three minutes using a rice cooker can kill up to 99.7 percent of germs, he said, adding that this method lowered the mask’s filter quality by the least — about 10 percent.
Soaking masks in alcohol or bleach for 10 minutes could lower their filter quality to 70 to 80 percent, he said, adding that the study was published in Indoor Air in 2018.
Lai said he also conducted a study using surgical masks and found that dry steaming them using a rice cooker was also more efficient than using alcohol or high-pressure sterilization.
Dry steaming the same mask five times gradually reduced its filter efficiency to 10 percent, he said.
When heating a mask, do not place it at the bottom of the cooker, where temperatures are high, he said, advising people to use a rack to support the inner pot containing the mask.
Masks can only be sterilized and reused if they have not been used in a hospital, do not contain too much saliva or other bodily fluids and are not damaged, he added.
A mask’s filter efficiency needs to be more than 80 percent to qualify, he said.
Asked about the tests, the Food and Drug Administration (FDA) said that spraying alcohol or high-temperature drying might damage the structure of masks and affect their protective effect.
FDA researcher Wang Chao-yi (王兆儀) said that she had not seen the test data on high-
temperature drying and, as such, could not say whether the method was appropriate.
The FDA only reviews and approves masks for one-time use, she said.
Wang reminded people who are healthy that they do not need to wear masks in outdoor places or places with good ventilation, while people with chronic illnesses or respiratory symptoms and those who are visiting hospitals should wear masks.
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