Researchers have found that heating N95 materials preserves their filtration efficiency for 50 cycles of disinfection.
The current shortage of medical PPE has meant that frontline workers battling against Covid-19 have been forced to reuse their equipment – most of which is only designed for single use.
Included in this shortage are N95 respirators and surgical masks – critical items that must be reserved for healthcare workers and other medical first responders, as recommended by the Centers for Disease Control and Prevention (CDC).
Now, researchers reporting in American Chemical Society (ACS) Nano have tested several methods for disinfecting N95 materials, finding that heating them preserves their filtration efficiency for 50 cycles of disinfection.
N95 masks contain a layer of meltblown polypropylene fibres that form a porous, breathable network. To help capture smaller particles that could slip through the holes, the fibres are electrostatically charged. The US Centers for Disease Control and Prevention has recommended several methods for disinfecting N95 masks, such as heating, ultraviolet (UV) radiation and bleach treatment, but so far they have not been tested extensively, especially for multiple rounds of disinfection.
Yi Cui and colleagues wanted to compare five of the methods that could reasonably be used within a hospital setting to see how mask materials hold up to repeated disinfections.
In this study, instead of analysing N95 masks – which should be reserved for healthcare workers – the researchers examined pieces of the meltblown fabric used to make these masks. They treated the material with a particular disinfectant and compared its ability to filter aerosol particles (resembling respiratory droplets, but lacking coronavirus) before and after disinfection.
The team found that spraying the fabric with an ethanol or chlorine bleach solution drastically reduced the filtration efficiency after only one treatment, from about 96% to 56% (ethanol) or 73% (bleach). A single steam treatment maintained filtration, but five steam treatments led to a sharp decline in efficiency. UV radiation allowed up to 20 cycles of disinfection; however, administering the exact dose of UV that kills the virus without damaging mask materials could be problematic, the researchers note.
The best disinfection method appeared to be heating. For example, heating at 185oF for 20 minutes allowed the fabric to be treated 50 times without loss of filtration efficiency. But frequently donning and removing N95 masks could affect fit, which also impacts performance, the researchers point out.
