Heat sterilization dramatically reduces filter efficiency of the majority of FFP2 and KN95 respirators

Abstract

Background Because of the enormous demand for personal protective equipment and especially respiratory protective devices (respirators) during the initial phase of the corona pandemic shortages arose. Sterilisation of used respirators can reduce these shortages. In our study, respirator testing was carried out after only one sterilisation cycle. Aim To determine if steam sterilisation and reuse could be safely applied for used respirators. Methods In a cabinet an aqueous solution of NaCl (0.02% w/v) was nebulized and passed through a sample of the material of a respirator. Passing particle concentrations were measured directly from the cabinet and via the filter material of the respirator for particles ≥ 0.3 μm, ≥ 0.5 μm and ≥ 1.0 μm. Findings only three out of ten steam sterilised respirators met the requirements of 94% filtration efficiency. Conclusion The results prove that heat sterilisation cannot be generically applied for reuse of respirators safely.

Recent developments in filtration media and respirator technology in response to COVID-19

“…The rate of dissipation can be a few hours to over a day depending on details of temperature, humidity, and use. Attempts to sterilize the respirator with heat, 25 ionizing radiation, 26 or disinfectant such as ethanol 27 degrade the filtration efficiency and the structural integrity of the respirators. While UV disinfection 28 does not degrade FE, it cannot penetrate to sterilize inner respirator layers.…”

Filtration efficiency of N95 filtering facepiece respirators during multi-cycles of ‘8-hour simulated donning + disinfection’

“…Previous studies have revealed some disinfection methods that can effectively inactivate microorganisms on respirators, including soap or hot water immersion, alcohol spraying, high-pressure steam, dry heating, UV radiation, and vaporized hydrogen peroxide [ 10 , 11 ]. However, since most current respirators use electret filters as the filtration materials, disinfection treatments in the form of aqueous solutions or steam, such as soap or hot water immersion, alcohol spraying, and high-pressure steam, will neutralize the static charge on the filters, resulting in a significant decrease in the filtration efficiency of respirators [ [12] , [13] , [14] , [15] , [16] , [17] , [18] ]. Dry heating, UV radiation, and vaporized hydrogen peroxide are disinfection methods that have been proven to be effective in inactivating microorganisms without compromising the respirator filtration efficiency [ 19 ].…”

Effective ultraviolet C light disinfection of respirators demonstrated in challenges with Geobacillus stearothermophilus spores and SARS-CoV-2 virus

“…In view of the shortages, some countries released guidelines for using respirators by healthcare workers and public [ 4 , 5 ]. To mitigate shortage, decontamination procedures were explored to allow for safe reuse [ [6] , [7] , [8] , [9] ]. A recent study [ 8 ] demonstrated that steam sterilization at 121 °C was not a generic option for respirator disinfection and appeared detrimental to many respirator brands.…”

“…To mitigate shortage, decontamination procedures were explored to allow for safe reuse [ [6] , [7] , [8] , [9] ]. A recent study [ 8 ] demonstrated that steam sterilization at 121 °C was not a generic option for respirator disinfection and appeared detrimental to many respirator brands. In-house testing was therefore advised to verify respirator quality for which simple tests have been established [ 8 , 10 ].…”

“…A recent study [ 8 ] demonstrated that steam sterilization at 121 °C was not a generic option for respirator disinfection and appeared detrimental to many respirator brands. In-house testing was therefore advised to verify respirator quality for which simple tests have been established [ 8 , 10 ]. Disinfection by UVC irradiation might be less harmful to respirator integrity.…”