Masks: steam to disinfect is not effective

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No, it is not possible to decontaminate it in 15 seconds with steam. When asked, experts explain why.

In this period of misunderstanding, the use of a mask for the general public is mandatory on public transport and in educational establishments and is recommended in certain situations (in stores in case of too large an influx, in companies) to protect themselves and protect others. For people who want to reuse their homemade cloth masks, it is not recommended to use a method presented in recent days on social media to disinfect them. A fake news that recommends placing them in a pot of boiling water for fifteen seconds, when this process is ineffective or even dangerous according to the experts contacted.

This post, already shared tens of thousands of times on Facebook since the end of April, further indicates that this method is applied independently of the masks (surgical, FFP2, tissue), and would be as effective as machine washing at 60 ° C for 30 minutes. This consists of putting a glass of water in a large frying pan, boiling the water and then rinsing the mask with the frying pan in the steam cloud for at least 15 seconds. Why is it really ineffective? "An unstable environment combined with such a short exposure period does not allow effective sterilization of the masks for reuse," said AFP.

Why is steam not recommended?

The agency first reminds that certain masks are not intended to be reused. This is the case of surgical masks and FFP2 since the latter are disposable masks, therefore, for single use only. He also cites an opinion of the Superior Council of Public Health (HCSP) dated April 29 and states that "FFP type masks cannot undergo a washing phase or irradiation treatment before any sterilization process, because they lose their electrostatic properties on the external face, with loss of filtration performance Surgical masks can "be washed, but with the risk of losing the anti-spray filtration performance".

Furthermore, questioned by AFP, Sylvie Raspaud, head of the pharmacy service at the Kremlin-Bicêtre hospital, in France explains that "the steam does not wash, on the contrary it fixes the residues on the surfaces." "This protocol is dangerous," said Philippe Cinquin, professor of public health at the University Hospital of Grenoble and director of the TIMC laboratory. The reason: a period of steam exposure that "seems excessively short."

If wet heat is more effective than dry heat, two parameters must be combined for effective sterilization, namely controlling the temperature and humidity level to which the mask is exposed, which is not the case with this method.

Add to this the fact that the Facebook post doesn't mention a crucial step in the sterilization process, which requires two steps. "The saying goes that we sterilize only what is clean. To remove any microorganism, including the virus, you must first clean it," says pharmacist Sylvie Raspaud. Therefore, it is better to resort to the recommendations of health agencies than to tutorials on social networks. The National Medicines Agency (ANSM) recommends, for example, machine wash at 60 ° C for at least 30 minutes with a suitable detergent for the fabric, then mechanically dry before ironing the mask at 120/130 ° C.

The government site advises using a blow dryer or hair dryer to dry the mask or air dry it on a disinfected surface.

But is it possible or not to wash it by hand? Yes, as long as you follow three steps, according to the head of the pharmacy service at the Kremlin-Bicêtre hospital. First, clean with a detergent product (soap, detergent, handwashing detergent). An essential act to eliminate "all the spots that leave the face, the mouth and the nose". However, be careful, the mask should not be brushed "so as not to damage the fabric fibers".

The mask must rest for 30 minutes in hot water at 60 ° C. Since it is difficult to know what temperature is used, AFP gives the trick of "soaking the mask in a pan on a baking sheet in boiling water. Finally, you must request the rinse, which should be as effective as a good hand wash.

Note that if wearing a mask adds a physical barrier, it is in no way a substitute for barrier measures, such as social distancing.

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