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article imageHeating can help to disinfect N95 face masks

By Tim Sandle     May 19, 2020 in Health
In an ideal world, face masks intended for single use are used for single use purposes. However, in cases of short supply, alternative mechanisms are being considered. Of different measures, heating can be partially effective.
While health workers are having little option in terms of reusing face masks, great care needs to be taken. Reuse of masks can leave the mask deformed and not forming a tight seal anymore; furthermore, treating the mask can affect its filtration efficiency.
Chemists have undertaken several methods to disinfect N95 grade materials. The findings indicate that heating face masks can preserve their filtration efficiency for up to 50 cycles of disinfection.
An N95 masks act as a barrier between the wearer and the surrounding environment to protect a person against hazardous fine particles and viruses suspended in the air. The reference to’N95’ relates to a U.S. standard, other standards for masks exist worldwide. For example, they are termed FFP2 respirators in Europe.
N95 masks contain a layer of "meltblown" polypropylene fibers. These form a porous, breathable network. So that smaller particles are captured, the fibers are electrostatically charged.
Some of the ideas proposed for disinfecting face masks include the application of heat, ultraviolet radiation and chemical treatment. These methods were examined by researchers, in terms of the ability of the mask to filter aerosol particles pre- and post-disinfection.
The least effective method was spraying the fabric with alcohol or chlorine solution (household bleach) as this significantly reduced the filtration efficiency, including following just one treatment,. The reductions were at such a level so that the masks were no longer able to filter viruses to an acceptable level.
Furthermore, a single steam treatment maintained the filtration efficacy; however, this declined following five steam treatments. UV radiation was successful 20 cycles of disinfection. A major complexity was with controlling the dose of UV.
In contrast, the optimal disinfection method heating. For example, heating at 85 degrees Celsius for 20 minutes was satisfactory and this allowed the fabric to be treated fifty times while maintaining filtration efficiency.
It is important to note that face masks carry an infection risk, and that hands should be washed with hot water and soap (or an alcohol-based sanitizer) prior to putting them or taking them off, and masks to be discarded should be disposed of in an appropriate receptacle. At all times a mask that has been worn, whether to be considered for re-use or for disposal, should be treated as an infectious waste item.
The research has been published in the journal ACS Nano, with the paper titled “Can N95 Respirators Be Reused after Disinfection? How Many Times?”
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