Kirurške maske za zaščito okolice, FFP2/3 za zaščito posameznika
Masks vs Respirators (link)
Before we go any further, lets just clarify on a technical difference between a “mask” and a “respirator”. In day to day language we often say mask, when referring to what are technically called respirators.
Uses for Masks:
- Masks are loose fitting, covering the nose and mouth
- Designed for one way protection, to capture bodily fluid leaving the wearer
- Example – worn during surgery to prevent coughing, sneezing, etc on the vulnerable patient
- Contrary to belief, masks are NOT designed to protect the wearer
- The vast majority of masks do not have a safety rating assigned to them (e.g. NIOSH or EN)
Uses for Respirators:
- Respirators are tight fitting masks, designed to create a facial seal
- Non-valved respirators provide good two way protection, by filtering both inflow and outflow of air
- These are designed protect the wearer (when worn properly), up to the safety rating of the mask
- Available as disposable, half face or full face
Whilst surgical style masks are not redundant by any means (discussed more below), they aren’t designed to protect the wearer, whilst respirators are.
|Respirator Standard||Filter Capacity (removes x% of of all particles that are 0.3 microns in diameter or larger)|
|FFP1 & P1||At least 80%|
|FFP2 & P2||At least 94%|
|N95||At least 95%|
|N99 & FFP3||At least 99%|
|P3||At least 99.95%|
|N100||At least 99.97%|
As you can see, the closest European equivalent to N95 are FFP2 / P2 rated respirators, which are rated at 94%, compared to the 95% of N95.
Valved respirators make it quicker and easier to exhale air than their non-valved counterparts. This makes them more comfortable to wear, and leads to less moisture build-up inside the respirator. This is particularly useful with the higher rated filters (N100/FFP3), which require more force to exhale through.
One important caveat though, is that valved respirators may not be optimal in settings where you want to stop the wearer from spreading infection. If the wearer is ill, the valve will mean that their out breath / coughs / sneezes will make their way through the mask, and into the air, without filtering. This is due to the valve opening when exhaling.
TL;DR – yes, respirators with high efficiency at 0.3 micron particle size (N95/FFP2 or better) can filter particles down to the size of the coronavirus (which is around 0.1 microns). What that doesn’t tell us is how much protection respirators will provide against coronavirus when in use – we will need to wait for future studies to confirm.
Respirator’s are measured by their efficiency at filtering particles of 0.3 microns and bigger (noting that the coronavirus is smaller than that).
The reason for the focus on 0.3 microns is because it is the “most penetrating particle size” (MPPS). Particles above this size move in ways we might anticipate, and will get trapped in a filter with gaps smaller than the particle size. Particles smaller than 0.3 microns exhibit what’s called brownian motion – which makes them easier to filter. Brownian motion refers to a phenomenon whereby the particle’s mass is small enough that it no longer travels unimpeded through the air. Instead it interacts with the molecules in the air (nitrogen, oxygen, etc), causing it to pinball between them, moving in an erratic pattern.
According to researchers this point between “normal” motion and brownian motion is the hardest particle size for filters to capture. What we can take away from this, is that high filter efficiency at 0.3 micron size will generally translate to high filter efficiency below this size also.
This article by 3M discusses research showing that all 6 of the N95 respirators they tested can efficiently filter lower than 0.1 micron size with approximately 94% efficiency or higher. The graph below is from that article, and illustrates this:
Additionally, smartfilters.com have a great article on this subject, citing research showing that the respirators tested could filter down to 0.007 microns (much smaller than Covid-19). For example the 3M 8812 respirator (FFP1 rated) was able to filter 96.6% of particles 0.007 microns or larger. Suggesting FFP2 or FFP3 would achieve even greater filtration.
The below image shows the size of the coronavirus, relative to other small molecules like a red blood cell, or the often talked about PM2.5 particle size.
Respirator Re-Use – How to sanitize them safely?
Research from SmartAirFilters (link) showed that after 11 days of heavy use in polluted Beijing, their respirator had only lost 1.4% of filtering capacity. So we know that disposable respirators can continue to function for more than 1 day/1 use – fortunately!
Whilst FFP2/FFP3 or N95/N100 are the gold standard as far as face protection goes, what about surgical masks, do they provide any protection?
Strictly speaking, surgical masks are primarily designed to protect vulnerable patients from medical professionals. Stopping the wearer (e.g. surgeon) from spreading their germs when coughing/sneezing/speaking. So they’re designed to protect patients, not to protect the wearer.
An obvious flaw with surgical masks compared to respirators is their lack of a tight face fit, which leaves gaps around the edges.
There isn’t currently research available on the efficacy of surgical masks (or even respirators), for protecting wearers against the coronavirus. This isn’t totally surprising given how new the virus is.
In lieu of that, the below looks at research around the use of surgical masks and N95 masks in the context of influenza, looking specifically at the protection given to the wearers. Influenza may be a good virus particle to compare it to, as they are both transmissible through droplets and aerosol, both cause respiratory infection, and both are similar in particle size.
N.B. Please don’t conflate the comparison to the influenza particle as suggestion that they are comparable illnesses – current data suggests that the coronavirus may have a higher mortality rate.
So where does this leave us? Those 2 studies suggest that surgical masks are approximately comparable to N95 masks when it comes to preventing influenza illness in close contact clinical settings. What this doesn’t tell us, is whether they’re better than wearing nothing on our faces.
To find that out, we need a study that has a control group that doesn’t use any facial protection. Due to ethical considerations, those studies aren’t abundant, but we do have at least one.
In this Australian study, they looked at 286 adults in 143 households who had children with influenza-like illness3. For clarity, influenza-like illness is not the same as laboratory confirmed influenza. It’s diagnosed by symptoms like fever, dry cough and feeling sick, which could mean influenza, but could also be caused by the common cold or other viruses. They found that adults who wore masks in the home were 4 times less likely than non-wearers to be infected by children in the household with a respiratory infection. There is nice analysis of the study here by Imperial College London.
It’s definitely fair to note that this Australian study was very small, and could not be considered definitive by any means. That being said, we’ve got to work with what he have, and this at least gives us some data points:
- Wearing a surgical mask or N95 (FFP2) respirator was better (in the study) at protecting against influenza-like illnesses than wearing nothing at all
- Whilst we can anticipate surgical masks to be inferior to respirators, the studies above suggest they are not as inferior as one might assume. For example the first two studies didn’t find a significant difference between surgical masks and N95 respirators, when protecting wearers against influenza.
- Important to note that we’ve used influenza protection as a proxy for SARS-CoV-2 (coronavirus). This is done because SARS-CoV-2 is new and there are no comparable studies on it. But of course the drawback is that it still leaves a lot of uncertainty, as SARS-CoV-2 may act quite differently in terms of transmission.
In a lab setting, with artificial conditions, we find that surgical masks are able to block 80% of particles down to 0.007 microns. Compared to the 3M 8812 respirator in this study which blocked 96% (FFP1 rated).