Electric Cookers Effectively Sterilize N95 Respirators

Photo by Chamteut Oh

Dentistry Today
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Photo by Chamteut Oh

Electric multicookers may be able to sanitize N95 respirator masks, report researchers at the University of Illinois Urbana-Champaign, enabling their safe reuse.

According to the researchers, 50 minutes of dry heat inside an electric cooker such as a rice cooker or Instant Pot decontaminated N95 respirators inside and out while maintaining their filtration and fit.

N95 respirator masks are considered the gold standard of personal protective equipment (PPE) in protecting wearers against airborne droplets and particles, such as the coronavirus that causes COVID-19, the researchers said.

“A cloth mask or surgical mask protects others from droplets the wearer might expel, but a respirator mask protects the wearer by filtering out smaller particles that might carry the virus,” said civil and environmental engineering professor Thanh “Helen” Nguyen, MS, MS, PhD.

High demand during the COVID-19 pandemic has created severe shortages for healthcare providers and other essential workers, prompting a search for creative approaches to sanitization, the researchers said.

“There are many different ways to sterilize something, but most of them will destroy the filtration or the fit of an N95 respirator,” said civil and environmental engineering professor Vishal Verma, MTech, PhD.

“Any sanitation method would need to decontaminate all surfaces of the respirator, but equally important is maintaining the filtration efficacy and the fit of the respirator to the face of the wearer. Otherwise, it will not offer the right protection,” said Verma.

The researchers hypothesized that dry heat might be a method to meet decontamination, filtration, and fit criteria without special preparation or leaving any chemical residue. They also wanted to find a method that would be widely acceptable for people at home.

They verified that one cooking cycle, which maintains the contents of the cooker at around 100°C or 212°F for 50 minutes, decontaminated the masks from four different classes of virus including a coronavirus and did so more effectively than ultraviolet light. Then, they tested the filtration and fit.

“We built a chamber in my aerosol-testing lab specifically to look at the filtration of the N95 respirators and measured particles going through it,” Verma said.

“The respirators maintained their filtration capacity of more than 95% and kept their fit, still properly seated on the wearer’s face, even after 20 cycles of decontamination in the electric cooker,” Verma said.

The heat must be dry heat. No water should be added. The temperature should be maintained at 100°C for 50 minutes. Also, a small towel should cover the bottom of the cooker to keep any part of the respirator from coming into direct contact with the heating element.

However, Nguyen said, multiple masks could be stacked to fit inside the cooker at the same time. The researchers created a video demonstrating the method.

The researchers see potential for the method to be useful for healthcare workers and first responders, especially those in smaller clinics or hospitals that do not have access to large-scale heat sanitization equipment.

The study, “Dry Heat as a Decontamination Method for N95 Respirator Reuse,” was published by Environmental Science and Technology Letters.

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