As health-care workers continue on the front lines of the novel coronavirus pandemic, quantities of personal protective equipment — particularly masks — have become an issue.
On Sunday, chief public health officer Dr. Theresa Tam said the Canadian government was exploring the possibility of sterilizing masks for reuse.
“It is one of the most important and, I think, worthwhile lines of pursuit for personal protective equipment right now,” she said.
There are several sterilization facilities in Canada that are likely capable of sterilizing N95 masks, most of which are already in the business of sterilizing consumer products, medical supplies, some foods and medical products like cannabis.
One such company, Nordion, along with two other companies owned by Sotera Health — Sterigenics and Nelson Labs — are already working with the Canadian government to evaluate methods to resterilize personal protective equipment.
The companies work with gamma irradiation, which they said acts as an effective method of reducing or eliminating a wide variety of micro-organisms, including viruses.
Another company, Mevex, uses a machine called an electron accelerator. The machine utilizes radiation to break down organisms and hinder a pathogen’s ability to reproduce — thereby killing the bacteria.
Mevex president David Brown told Global News “it’s a complicated process” but that it works and could sterilize “millions” of N95 masks per day.
‘Gross’ but safe
N95 masks already undergo a round of sterilization after they’re first manufactured. Brown said manufacturers will often send their products to facilities with electron accelerators to kill off any microbes or bacteria that may have attached themselves to the masks while they were being made.
But when it comes to resterilizing, which would mean additional radiation, “we need to understand how they’re contaminated — not just with the microbes, but with whatever else happens during their use.”
He also noted that cleaning and sterilizing a mask are two separate things.
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If a mask becomes soiled, either by saliva or dirt, for example, and goes through an electron accelerator, he said the mask will become sterile, but the saliva and dirt would still remain on the mask.
Cleaning an N95 mask, which is made with a paper filter, could also be difficult.
Without first cleaning a batch of N95 masks before putting them through for sterilization, Brown said “it would be gross” but still more or less safe.
Irradiating a mask for a second time also presents its own set of challenges.
Imagine a rubber band that’s been left out in the sun for too long. After a while, it becomes brittle, and the elastic has a higher tendency to snap.
Similarly, Brown said materials often used to create masks such as plastic are degraded by radiation.
“Every time you radiate something, it damages it,” Brown said. “So it’s a competition between getting the goodness of the sterilization effect and mitigating the damaging effect of the radiation on the materials.”
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Brown noted that the number of times a piece of equipment can be sterilized depends on the materials from which it’s made, but usually, there is a margin of two or three times per sterilization dose before an item like an N95 mask will become damaged beyond use.
‘We’re winging it’
Bill Anderson, a chemical engineering professor at the University of Waterloo, said it would be difficult to clean any mask that was too visibly or heavily soiled.
“There’s no real way to clean it because of the materials that they’re made of,” he said. “You can’t really stick it in water very easily or in other cleaning solutions and be confident that you’ve actually removed very much.”
Anderson said the safest measure would be not to reuse the masks at all, but in the case of a shortage, “it’s safer to run it through some sort of a process which has been set up properly and validated than to just reuse it day after day with no real process.”
Ron Hoffman, a University of Toronto professor in the school’s civil and mineral engineering department, said it’s important to remember that personal protective equipment like an N95 mask was “never designed to be reused.”
Yes, masks can be sterilized and disinfected, but Hoffman said the medical community has not had enough time to create effective protocols with abject certainty.
He said masks that have been soiled in any visible way should be disqualified from the process. The masks already have a “certain depth” to them that makes them stronger than regular masks.
“The problem is that if the viruses get trapped within the depths of this mask, it might be harder for the disinfectant to penetrate into that depth and get at the viruses that have been trapped inside the filter of this mask,” said Hoffman.
He said there are three types of disinfectant technology that those in the medical community are looking at using on personal protective equipment in North America.
They involve either “heat-treating” the masks by warming them to around 80 C for a certain period of time, using ultraviolet light to kill micro-organisms or using hydrogen peroxide vapours to treat them.
Each of them, Hoffman said, has strengths and weaknesses.
“The trick with disinfecting is that you want to disinfect the virus without actually physically destroying the mask,” said Hoffman. “If you heat it too much, you’ll actually destroy the mask.”
With the ultraviolet wavelength, which involves shining a light onto the mask for approximately 10 minutes, there is no chemical needed.
“But if you have a virus that’s trapped, let’s say in a little crevice or shadow of the mask… it’s like shining a flashlight on something hidden in the shadows. It’s not going to be eliminated.”
Hoffman added that the vapour found in hydrogen peroxide — which is a crucial ingredient in antiseptics like hand sanitizer — can effectively kill the bacteria in masks, but a dependency on this method also runs the risk of a supply shortage.
However, none of these technologies are guaranteed to work 100 per cent.
“Up until the last one or two weeks, this was kind of all a theoretical thing that some people had explored in a very rudimentary way,” he said.
To do these types of studies properly, Hoffman said it would take months and months, “if not years and years” to develop a foolproof method.
With that in mind, he said these technologies are not new and have been proven to help in other scenarios.
“We’re winging it but using very good educated guesses about it,” he said. “It’s still very much rapid response and trying to make the best of a bad situation.”
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