Fifty minutes of dry heat in an electric cooker, such as a rice cooker or Instant Pot, could effectively sanitise N95 respirator masks, while maintaining their filtration and fit, researchers, including one of Indian origin, have found.
According to the findings published in the journal Environmental Science and Technology Letters, this could enable wearers to safely reuse limited supplies of the respirators, originally intended to be one-time-use items.
N95 respirator masks are the gold standard of personal protective equipment that protect the wearer against airborne droplets and particles, such as the coronavirus that causes COVID-19.
"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 Thanh Nguyen, professor at the University of Illinois Urbana-Champaign in the US.
High demand during the COVID-19 pandemic has created severe shortages for health care providers and other essential workers, prompting a search for creative approaches to sanitization.
"There are many different ways to sterilise something, but most of them will destroy the filtration or the fit of an N95 respirator," said Professor Vishal Verma from the University of Illinois.
"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," Verma said.
The researchers see potential for the electric-cooker method to be useful for health care workers and first responders, especially those in smaller clinics or hospitals that do not have access to large-scale heat sanitisation equipment.
It may be useful for others who may have an N95 respirator at home -- for example, from a pre-pandemic home-improvement project -- and wish to reuse it, they said.
The researchers hypothesised that dry heat might be a method to meet all three criteria -- decontamination, filtration and fit -- without requiring special preparation or leaving any chemical residue.
They also wanted to find a method that would be widely accessible for people at home.
The team decided to test an electric cooker, a type of device many people have in their pantries.
They verified that one cooking cycle, which maintains the contents of the cooker at around 100 degrees Celsius for 50 minutes, decontaminated the masks, inside and out, from four different classes of virus, including a coronavirus -- and did so more effectively than ultraviolet light.
"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 per cent and kept their fit, still properly seated on the wearer's face, even after 20 cycles of decontamination in the electric cooker," he said.
The researchers note that the heat must be dry heat -- no water added to the cooker, the temperature should be maintained at 100 degrees Celsius for 50 minutes and 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, multiple masks can be stacked to fit inside the cooker at the same time, Nguyen added.