Zojirushi NS-ZCC10 Rice Cooker
In the face of demand caused by the Covid-19 pandemic, the Centers for Disease Control have laid out strategies for optimizing the supply of N95 respirators, one of the most popular pieces of PPE. Healthcare workers are often expected to reuse their N95 masks multiple times before discarding them. However, the masks may become infected during interactions with coronavirus patients, putting the wearer at risk to contract the virus when they remove and reapply the mask many times.
The solution to mitigate the risk posed by reuse may be found in an unexpected place — your kitchen!
Research shows N95 masks can be effectively decontaminated with electric cookers. A new paper by researchers from the University of Illinois describes how the team used an electric cooker to give N95 respirators dry heat treatments which disinfected them without compromising their efficiency.
Back in February, before coronavirus lockdowns began to sweep across the United States, researchers at Chung Shan Medical University in Taiwan experimented with a variety of possible sterilization methods for N95 respirators. Their results showed soaking the masks in bleach or alcohol lowered their filtration efficiency drastically. However, dry heating them in a rice cooker effectively sterilized the masks while causing the least amount of damage to filtration of any other tested method.
Taiwan’s Health Minister Chen Shih-chung even promoted the rice cooker method by demonstrating it at a Central Epidemic Command Center press conference in April. In July, scientists from Case Western Reserve University wrote about their results from using a rice cooker a decontamination tool. They suggested the answer wasn’t heat but humidity, saying kitchen steamers could effectively deactivate viruses on cloth masks.
The University of Illinois researchers differentiated their study from previous research by putting an emphasis on and testing according to the four recommendations for N95 respirator reuse laid out by 3M, the main manufacturer of the popular mask.
For successful decontamination, 3M states the method has to inactivate the target virus, not cause damage to filtration ability, not affect fit, and not leave behind potentially harmful chemicals for the wearer.
The researchers used a Faberware pressure cooker — a relatively inexpensive and common appliance — for the experiments. They conducted the tests on four different viruses, including Tulane virus and rotavirus, to see how effectively the method is at decontamination. The team put the viruses on the mask’s strap, inside edge, inside center, outside edge and outside center.
After 50 minutes at 100 degree Celsius heat in the electric cooker, they calculated all viruses on the masks had experienced a reduction in integrity of the binding protein and the capsid protein — the shell which encloses the virus’s genetic material. They found each virus tested was inactivated by at least 99.9 percent over the course of the treatment.
Before being placed in the electric cooker, the N95 had a more than 99 percent efficiency at filtering out particles. After 20 cycles of 50 minute dry heat treatments in the pressure cooker, the efficiency only dropped to 95 percent.
To ensure the 20 cycles of treatment had not significantly altered the fit of the respirators, the researchers put the treated masks through rigorous fit testing. Participants wore the treated N95 respirators in a test room filled with sodium chloride (NaCl) aerosol and completed a series of exercises including talking, turning their heads from side to side, and nodding. Afterwards, the ratio of NaCl concentration in the air to that inside the mask was measured. Each mask had a calculated fit factor of greater than 100 — a passing grade for the test.
For those wanting to treat their respirators in electric cookers at home, the researchers posted a YouTube video laying out the process. They suggest lining the cooker with a towel because the temperatures of the inside pot walls get hot enough to melt and damage the respirators if they come into direct contact. The video also notes that several masks can be disinfected inside the cooker at one time.
This research could be particularly helpful for health care workers, though the researchers noted further tests are needed on different types of respirators because different materials could require different temperatures and times for decontamination.