Coronavirus - worldwide spread and control

This paper provides an interesting definition of aerosols (small droplets) versus large droplets in the context of pathogen transmission. To quote:

So if a pathogen is spread by aerosol (small droplets), face masks which are not close fitting will not be effective, as aerosols can get in, traveling with the airflow that enters through the loose sides of the mask.

However, a tighter-fitting mask will offer protection: the paper says pathogens which are transmitted by aerosol include tuberculosis, measles and chickenpox, and protection from these requires tighter-fitting N95 masks rather than standard surgical masks.

The US N95 mask is similar to the European FFP2 mask. And the higher standard N99 mask (equivalent to FFP3 masks) would also help block aerosol transmission. See respirator specs.


Whereas if a pathogen is not spread by aerosol, but is spread by large droplets, then a regular surgical mask will help (blocking large particle entry to the nose and mouth if someone coughs or sneezes in close proximity to you).

 

If it’s aerosol (small-ish) particles, then your mask has to fit closely to actually work. For ‘serious’ use there’s actually training and a test fit kit to accomplish the correct fit. Don’t forget your eyes, that’s a possible route.

 

Anyone know how to sterilize one of those disposable (but not that cheap) N95/N99 masks? Would a cool oven (170 F) for half an hour do it? IDK at what temp the materials start breaking down, they’re obviously not meant for temps higher than humans can tolerate.

 

Most micro-organisms do not survive more than a few minutes at 80 Celsius (176F). As I understand it viruses of this sort tend not to like being completely dried out and away from host environment for very long anyway. 100 Celsius kills almost anything (212F) except strange spore forming bacteria/fungi. I don't know what N95/99 makes are made of but most plastics cope with 212F except things like plastic drink bottles that buckle. A lot of medical stuff is designed to be autoclaved - which means pressure cooking at quite a bit higher than 212F - maybe nearer 250.

 

They are not designed to be sterilized, unfortunately. They are single use.

Edit to add:

Source : https://www.fda.gov/medical-devices...t-infection-control/masks-and-n95-respirators

 

I feel sorry for those people stuck on the cruise ship that have been turned away by 5 countries. They're just stuck.

 

I've got a pack of FFP3 dust masks, which I occasionally use when doing DIY which creates fine dust.

I've always found that the place the air gets in past the filter is by the bridge of the nose, because the mask does not always precisely follow the contours of the top of the nose. These masks have a metal strip that you are supposed to bend to fit the nose contours; but because the metal is a bit weak on my masks, I find it tends to unbend as a result of the force from the elastic straps that hold the mask on.

A better option might be one of these more professional rubber dust masks, which fit the face more closely. You can buy one for about £5 or so. But it would look like some kind of sci-fi movie if you went shopping with one of those! Unless of course the virus hits Western cities in the same way it has hit Wuhan. In which case, a rubber face mask would not look sci-fi, just sensible!

I think soaking the mask in isopropyl alcohol would sterilize it in 30 seconds. If you look at table 2 of this interesting Feb 2020 paper on disinfectants for coronavirus, you see that isopropyl alcohol (2-propanol) and ethanol are very effective. It might also help wash the mask.

Note that the table shows povidone-iodine, even just a 0.23% solution, is a remarkably effective disinfectant for coronavirus. This is what surgeons use to disinfect their hands before an operation. Povidone-iodine has the advantage of being a persistent disinfectant: it continues protecting the skin hours after it is applied. Whereas alcohol quickly evaporates from the skin, so although it sterilizes, it does not offer any persistent protection from re-infection of the hands.

It might be an idea to make up a 0.23% hand sanitizer with povidone-iodine. You can buy 10% povidone-iodine online (that possibly 10% may be a bit too strong though for regular use, because quite a bit of the iodine is systemically absorbed). Then you could apply this 0.23% povidone-iodine hand sanitizer before you go out shopping etc, and it would help protect the hands from contamination. Also has the advantage of not drying out the skin like alcohol hand sanitizers.

 

No, no, no. You cannot sterilize a face mask by soaking it in alcohol. The N95 are designed for a single use, 8 hours work if you will, provided they do not get wet. The other concern i would have would be the chemical exposure of the product used to ‘sterilize’ which is not the right term.

N-95 are designed for fine droplets, providing you have a good seal on all edge surfaces with the skin. You should avoid touching the mask with (potentially contaminated) hands and avoid get it wet. Once you have exited the high risk area, you should dispose of the mask and wash your hands for at least 20 seconds.

 

Notice anything?

Confirmed nCoV cases could peak out at as little as 60,000-70,000. The rate of new infections each day has already slowed down significantly.

 

You seem very sure about that, where are you getting the info from? I cannot see why in principle heat or pure alcohol cannot be used to sterilize the material of a mask.

What is it that you think prevents a mask from working after 8 hours, in terms of blocking the ingress of pathogens?


Just found this article which says:

I am not sure if he is referring to surgical masks or to N95 / FFP2 masks.


Obviously you might normally throw a N95 / FFP2 mask away after a day's use, especially if using it for dusty work, and the dust collects in the mask fabric. But we are talking about circumstances where there may be a shortage of masks.

 

https://www.cdc.gov/niosh/topics/hcwcontrols/recommendedguidanceextuse.html

8 hours is the recommended single use time (after which, assuming there is supply, a fresh mask should be used)

Over time the surface of the mask inevitably becomes contaminated and airflow through the mask may become increasingly restricted. Over time the edges of the mask wear leading to fit degradation. The air coming in through a poor fitting mask may compensate for the extra resistance in breathing through the mask, leading an increase in unfiltered air (hypothesis - mine).

Using liquid on a mask will both push particulate into it and lead to increased air resistance.

Isopropyl alcohol should never be used on something you are going to breathe through (extrapolated from my knowledge of its properties).

Masks should not be touched, even when putting them on clean surgical gloves should be worn to avoid contamination of the mask surface.

etc.

 

If you are using it in dusty working conditions, it might become clogged after a while. But if you are breathing fresh air, I would think it would last much longer.

Isopropyl alcohol is very volatile, and will evaporate from the mask very quickly, leaving the material clean and sterile.

(Well, at least sterile with respect to bacteria and enveloped viruses; but intriguingly isopropyl alcohol does not work for non-enveloped viruses, whereas ethanol works for all types of virus).

 

I am 100% sure because i am a nurse and i received formal training on isolation and infection control. There has been no safety testing on a safe procedure to disinfect a mask. While disinfecting a smooth surface may be easy using isopropyl alcohol, the same cannot be assumed for a porous and delicate fabric like surface that needs to protect you agains virus-containing droplets.

Surgical masks are not sufficient to protect people from virus-containing droplets-people need to be aware of that. Just breathing into them will weaken the surface due to the amount of vapor that is exhaled. It may do the trick if you are simply going to the grocery store and you are not exposed to anybody coughing around you. However the first protection will always be hand washing and avoiding contacts with your face.

N-95 masks will provide protection against virus if certain conditions are maintained: the mask does not leak from any sides, the mask is not wet, and proper hygiene is maintained (wash hands before putting mask on and after removing the mask). These masks are fairly uncomfortable to wear (it gets hot, itchy and uncomfortable)- it is not easy to breathe (the flow of air is restricted, and it would be a good sign of tight seal) and it is hard to talk and understand others who speak through the mask.

In case of a pandemic, the best bet would be to stay home and avoid outside contact. If you must go out, avoid rush hour, bring hand sanitizer, avoid coughing people, avoid small spaces with people, and minimize contacts (handshakes, touching doors, light switches, touch screens, elevator buttons, hand rails)- or use hand sanitizer after each contact. Getting grocery delivered would be a good way of minimizing risk, in case of highly endemic areas.

In general, masks provide a false sense of security, especially using the cheap disposable masks.

 

There are reports in Asian media outlets of China having changed the definition of a "confirmed case", e.g. here

"The daily reports of Wuhan virus infections in China will likely begin to drop as the government has decided to stop counting patients who test positive for the disease but do not exhibit symptoms as "confirmed cases."'

A journalist asked the WHO yesterday if they are aware of that. They said "no". (here at 26:40)

So depending on who defines what as a "confirmed case" the numbers might be misleading.

 

Incredibly frustrating if the (lowering of) reported numbers is due to more fudging like this! Sigh.

 

Correction here. Alcohol disinfects but does not sterilize. Big difference. You need heat and pressure to sterilize, such as in an autoclave.

 

The Graph is from showleopard, I messed up the quotation

 

I appreciate it has not been tested, but that does not mean it will not work. Though I take your point about the alcohol perhaps not reaching all nooks and crannies of the mask and the dirt therein. In this respect, oven heat would be a more effective way to sterilize a mask.

Yes true, there is a difference between disinfection (reducing microbial levels) and sterilization (killing all microbes).

Though if you reduce viral levels enough, that also greatly helps prevent getting an infection. In the above paper I mentioned, ethanol was able to reduce viral infectivity of the SARS coronavirus by 5 log (a 100,000-fold reduction) after just 30 seconds.