Bridging the Gaps Between WHO and Aerosol Scientists (Part II)
Face masks in the middle of a controversy
It might be that the WHO’s reluctance to recognize aerosols as the predominant form of transmission of COVID-19 is not only grounded on scientific evidence but also on the market availability of the different protection measures. In other words, fear of a worldwide shortage of respirators may be delaying WHO acceptance of the prevalence of airborne transmission of SARS-CoV-2. If they do, countries would have to provide respirators to all workers in risk situations.
Aerosol scientists ask for universal masking and respirators at least for health care workers (HCWs) and high-risk situations and professions.
WHO argues that some jurisdictions have limited access to particulate respirators and risk domestic or global supply disruptions.
However, the fact that there are not (or there cannot be) respirators for everyone at risk should not delay the WHO’s acceptance of aerosols as a major route of transmission of COVID-19. Because there are options. In this article, we will see what we can do to increase safety in a situation of probable shortage of masks or respirators.
The decisions of WHO and governments take science into account, but also social and economic issues, very variable throughout the world
At the beginning of the pandemic, they told us: «Mask do not work, there is no evidence» or «Use masks only if you are ill». The reason? There weren’t enough masks for everyone. HCWs did not get enough protection. Nobody had.
Meanwhile, Asia immediately implemented largely airborne preventive measures: masks and ventilation.
Almost all countries need many more face masks than they have
Why do they not produce respirators and surgical masks? Because, even if production increased dramatically, they do not have enough raw materials or machinery to manufacture all the Personal Protection Equipment (PPE) masks that any country needs. The material that respirators are made of is challenging to manufacture. They are polymeric fibers melted and blown at very high speeds on a support, thus obtaining fibers with very small diameters.
Fit is essential in all masks (see Part I)
So far, we have neglected mask fit because regulators have not considered the predominant role of aerosols in the transmission of SARS-CoV-2 (if the transmission of the virus were by drops, the fitting would not matter). Manufacturers and regulators pay more attention to the filter material than to the fit.
Efforts in the design of new masks should focus on improving the fit, rather than improving the filter material.
Oversimplifying can be detrimental
We cannot merely divide mask into respirators and surgical masks. We should distinguish between masks that fit and masks that do not fit. Instead of focus on respirators, people should become familiar with ways to test a mask fit.
As we saw in Part I of this article, probably we idealize the effectiveness of the respirators. Usually, their protective effects have been studied in laboratories under ideal conditions. But as they are used in the real world, the overall efficiency at blocking emission and inhalation of respiratory aerosol particles will be lower (sometimes much lower) than expected.
If we only accept respirators as an efficient form of protection, it could happen that:
- Very poor quality respirators enter the market. Throughout the pandemic, low-quality respirators and masks have flooded the market. In some countries, it is challenging to find out if we have bought a mask according to the regulation. But even if the respirator is conforming, we must know that the so-called FFP2 earmuff-type masks (with rubber bands to hold them on the ears) are far from the originals (the ones with straps to adjust them behind the head).
To prevent shortage, some quality control measures have been relaxed, i.e., in Spain and other countries, the original FFP2s (with straps to adjust them behind the head) have been replaced by “FFP2” with ear loops. Even if these products fall into the category of respirators (they have the correct certificate), air flows through the edges. When acquired by hospitals to protect HCWs, workers attempt to improve the fit by using an ear-saver or a double mask (above or below the “respirator”).
People like these so-called «FFP2» with ear loops because it is not difficult to breathe with them. This is not surprising since a very high proportion of the air is not passing through the filter. However, we would not use leaky masks to avoid exposure to, for example, crystalline silica or asbestos fiber. Similarly, we should not use these leaky masks to protect us against a virus transmitted (mainly or to some extent — WHO — ) by aerosols. More worrying is that these «FFP2» with ear loops are being bought in hospitals to protect health-care workers since they have the correct certificate. - Asking the general public to use a more restrictive mask is just asking for problems. People will not be wearing them correctly. Before COVID-19, respirators were meant to be worn for short periods in high-risk situations. Wearing them correctly for long periods is uncomfortable. The use of uncomfortable respiratory protection in situations where this is not justified carries the risk of discouraging the use of any type of mask and is therefore counterproductive.
Respirators are optimized for fit and filtration. Still, they require fit testing. A good fit takes a lot of time and skill. The respirator must be molded until a complete seal is achieved. Most people do not do well with commercially available N95 or FFP2 type masks.
What can we do?
There are many masks on the market with suitable filtration materials. We have to focus our efforts on improving the fit.
Option 1: use a double mask.
Although various health authorities have recommended this approach, it is not probably the best option. The disadvantages of this double mask system are:
A. It is more expensive and inconvenient.
B. It is harder to breathe with a double mask.
The performance of any mask can be increased by layering materials, but only up to a point. As layers increase, particle capture is not additive, but pressure drop is additive. The same happens when layering masks; the more masks we wear, the worse we breathe.
The effectiveness of a mask and the breathing resistance are inversely related. The more difficult it is for the air to pass through the mask, the more it will pass over the edges, which will decrease the mask’s effectiveness (air will follow the path of least resistance).
Wearing two masks is not the same as doubling the protection. It may improve the seal, but it will lower the air resistance in an additive way.
The only situation in which it could be more appropriate to use a double mask is that of health workers who are in contact with patients, to avoid splashing biological fluids and thus protect the inner mask (respirator).
Problems associated with increased shortness of breath:
— We will be more uncomfortable. Therefore, we will touch masks more. We will try to adjust and move them. We will have to place and adjust more items, wash more items, be aware of more items.
And because of being more uncomfortable, we will probably wear them less time than it would be appropriate.
Besides, they will become more humid (having multiple layers, the evaporation of the exhaled moist air will be less). This humidity could adversely affect filtration if the filter media is electrostatically charged. The more coats, the more moisturized and the longer it takes for the masks to dry.
— There will be more leaks. Resistance to the passage of air is detrimental. The more difficult it is for the air to pass through the mask, the more it will tend to pass over the edges, which will decrease the mask’s effectiveness (as we have seen, air always tends to flow where it has the least resistance).
— We will tend to breathe more through the mouth, especially when breathing is more agitated, when we move. If the inhaled air does not pass through the nose, the protective ciliary barrier of the nose is rendered useless, which increases the tendency to have infections by respiratory pathogens.
Why add more layers and make it more difficult to breathe if we can improve the fit easily (option 2)?
Option 2: Wear a surgical or a procedure mask with an adjuster.
One of the most advisable ways to improve the fit is to wear a surgical or a procedure mask with an adjuster. Surgical and procedure masks can substantially reduce aerosol emission and inhalation when properly fitted with an adjuster device.
The effect of these two adjusters has recently been studied: the Badger seal mask fitter (left) and the FTM mask brace (right).
By using either of the two models tested, poor or medium performance masks become excellent masks, with filtration efficiencies close to respirators.
This image perfectly illustrates that inexpensive, single-use masks can substantially reduce aerosol emissions when properly fitted with a fitting device.
These accessories are expected to improve fit to a greater extent than a double mask, because they are designed to do so. And they will do it without making breathing difficult.
Surgical masks and procedure masks can substantially reduce aerosol emission and inhalation when properly fitted with an adjuster device.
And why a procedure or a surgical mask? Because it is only recommended to use these adjusters with masks with excellent breathability (differential pressure less than 40 Pa, in the study’s conditions). This condition is only met by some types of surgical or procedure masks, but not respirators.
When you consider fit, things are not so simple.
The need for respirators should therefore be calibrated to degree of risk. N95 respirators are optimized for fit and filtration but require fit testing, can be uncomfortable to wear for long periods, and are sometimes in short supply.
Option 3: Wear a mask (respirator, surgical mask, or cloth mask) with an outer layer of nylon.
If a cut nylon stocking is placed over any mask with side leaks (including surgical masks), the mask’s effectiveness improves by 15 to 50%.
Unlike a double mask, an outer layer of nylon can help ensure a better seal without making it difficult to breathe.
Even if it’s a bit strange, it works great because it improves the fit and adds a layer of electrostatic charge (the nylon), which helps to capture particles.
It is not a novel system, it was already proposed in 1983 for cloth, surgical and N95 masks.
The nylon hosiery material held the commercial mask [3M 8710] to the face so well that its leakage was reduced from 17 per cent to 0 per cent, suggesting the incorporation of such nylon material in commercial masks to form a particularly effective combination for respiratory protection.
If we use respirators, ideally we should:
- Choose a good model, preferably with a behind-the-head fit.
- If we are in high-risk places or situations, place a layer of nylon over the mask, since it is difficult to get a good fit and perform a self-test (see part I of this article). ( It is important to be clear that, unfortunately, today the acronym “FFP2” is not a guarantee that the mask is equivalent to a traditional FFP2. )
Option 4: use an elastomeric mask.
With these masks, fit problems would end. These masks have a filter equivalent to that of the FFP2 or N95, a plastic mold and a silicone contour, so that the seal is effective. Users find them more comfortable than N95 or FFP2 respirators. The drawback is that this masks (the comfortable models like the one in the photo) are sold in the United States, but not yet in other countries.
Another advantageous solution for pandemic times: reuse respirators
These questions are very common: “Can we reuse a respirator?” “How often?” “For how many hours?”
The first thing to say is that there are few financial incentives for respirator manufacturers to determine how to reuse these products. The best advice would be: if you can get enough masks, buy a few units of a good model. Mark them (for example, with a label attached to the tapes), quarantine them 5–7 days after each use, and reuse them a few times (5 to 10 times), in order of use.
How many times? It depends on the use. The most critical part of a respirator is not the filter material, which is very robust, but the elastic strips or bands. If the rubbers are deformed, or the mask does not fit as it did initially, it must be discarded.
If we use it in clean environments (in the office, in class, in the supermarket, etc.) we could use it in total up to 30–40 hours, as long as it is not dirty. This video shows the changes in the effectiveness of a mask reused multiple times, up to 30–40 hours. In the worst case (stored loosely in the car, with large temperature changes, for about 40 hours), the mask’s initial effectiveness was only reduced by 3%, at most.
So why is it usually said that this type of mask can only be used for 8 hours? Since originally they were used in highly polluted environments, with many suspended particles (industry, mining, fires, etc.). Over time, these suspended particles block the filters, which is noticeable because it will be more challenging to breathe.
Some purists probably will disagree, but for many people who cannot afford to change their respirator every 8 hours, reusing a good mask used in a “clean” environment is a better solution than using a mask always new but of lower quality.
Bridging the Gaps
The fact that there are not (or there cannot be) respirators for everyone at risk should not delay the WHO’s acceptance of aerosols as a major route of transmission of COVID-19. In a nutshell, the access to respirators should not delay the WHO to adhere to scientific evidence. WHO should review its health guidance and practical advice to highlight the relevance of aerosols in transmission.
The need for respirators should be calibrated to the degree of risk. They likely add the most value when caring for patients with known or suspected COVID-19. The marginal value of respirators outside of these circumstances may be less, but dedicated studies are needed. We need more data from real world.
But, even if respirators demonstrated to be more protective in real situations, we have options to increase safety in a situation of potential shortage. There are alternatives to respirators and ways to increase and improve their use. Combining suitable filtration materials and mask fitters provides alternatives with filtration efficiencies close to well-fitting FFP2 or N95 respirators.
