“When multiple sterilizations were applied, facepieces were soiled before each autoclave treatment to mimic the device usage in air environments contaminated with protein that may be associated with emission of pathogenic virions by infected persons,” according to the study. Researchers chose to perform five soil and sterilization cycles to simulate a daily reuse of the filtering facepiece over a period of five days.
Grinshpun also says that N95 respirators and some surgical masks rely on fibers that have an electrostatic charge which allows them to capture small particles and protect the wearer. Autoclaving and alcohol treatment weaken this electrostatic charge.
“What happens when you subject something to alcohol, heat or steam?” asks Grinshpun. “These fibers will lose, maybe not entirely, but at least some of their electric charge. This has a detrimental effect on the filter performance so that these protective devices may not be able to capture aerosol participles, including coronaviruses, as efficiently anymore.”
For some N95 respirators their collection efficiency can drop below their certification level of 95% for the most penetrating particle sizes, says Grinshpun.
He adds that performance of surgical masks changes as a result of autoclaving, whether the mask is soiled or not, with the effect being more pronounced for devices which had poor initial filtration capabilities.
He says instead of using autoclaving or ethanol alcohol to disinfect face masks and N95 respirator facepieces, alternative options such as ultraviolet light may be explored. Grinshpun’s study did not look at UV primarily because the investigators intended first to examine methods that are readily available in hospitals.
“We anticipated that UV-based and probably other techniques may be almost as efficient as autoclaving and ethanol treatment in inactivating pathogens but at the same time would not damage the fibers of protective detectives so that the particle collection efficiency will not suffer,” says Grinshpun. “Similar studies can and should be conducted with alternative decontamination methods.”
“The question of how the disinfection treatments impact the performance and integrity of respiratory protective devices remains important for as long as healthcare workers have to reuse these devices due to their shortage of personal protective equipment,” says Grinshpun.
Featured image of Sergey Grinshpun, PhD, in his lab by Colleen Kelley/UC Creative + Brand.