For those seeking increased protection through the coronavirus pandemic, it is important to understand the differences between facemasks and respirators and the level of protection they offer, writes Roland Tan, FAIHS/ChOHSP.
The general public in Australia has been advised by the Department of Health that they do not need to wear surgical masks in public or when in contact with others in an enclosed space unless they are: sick and coughing; looking after people suspected of COVID-19 infection; suspected of being infected by a primary care provider; or having returned from a country or region deemed high or moderate risk for COVID-19.
This advice is aligned with the World Health Organization (WHO) in the belief that the use of surgical masks or N95/P2 respirators are unnecessary as there is insufficient evidence supporting their use by healthy people to prevent transmission in public. Both Australia and the WHO further explain that there is a shortage of face masks which are needed by healthcare workers. This view is not universally held across Australia or globally.
Expert opinions in Australia also cite that not all masks are created equal, that the N95 masks cannot be safety reprocessed and that home-made surgical and N95 face masks need to be lab tested to assure their effectiveness.
Recent events have supported the concerns over the quality and safety of face masks and respirators; Chinese and Australian authorities are mitigating this issue through assuring appropriate documentation and inspections of these items.
Aside from sneezing and coughing, breathing and speech can emit large quantities of droplets and droplet nuclei (aerosols) averaging 1um in diameter. Research by the National Institute of Health (NIH) in the USA revealed that slightly damp washcloth over speaker’s mouth would significantly prevent the release of droplets and aerosols.
A recent study by Yale University has revealed that cloth face masks can reduce the growth rate of infections and deaths by as much as 10 per cent; the economic benefit was estimated between $3000 to $6000 for every additional masks worn in public.
Healthcare workers have been assured of adequate provision of appropriate face masks according to Dr. Nick Coatsworth, Deputy Chief Medical Officer on the 11 April 2020. The national medical stockpile and commonwealth collaboration with local manufacturers (e.g. SA and Victoria) has assured the adequate supply of face masks.
Availability of face masks and respirators at local Australian stores
Various types of face masks are currently available online and in some local stores (e.g. RSEA, Office Works, Bunnings, Mitre 10); however, there have been reports and complaints that face masks are pricey, may not be effective, are unreliable and even unsafe. The Therapeutic Goods Authority (TGA) in Australia maintains a list of approved products and suppliers in its register for surgical masks and P2 respirators. In a recent sampling test of surgical masks and N95 respirators manufactured in China revealed they did effectively provide the filtration standard expected; however, the authenticity of the claims that the PPEs met their international standard could not be validated arising from the unavailability of their certificates of approval.
Types of face masks and their effectiveness
There are essentially three types of face masks: cloth, surgical and N95 respirators; they are all considered disposable devices.
Cloth face masks have varying effectiveness, depending on their fabric and manufacture, in preventing the transmission of virus arising from their filtering efficiency, fit and comfort. They are less efficacious compared to surgical masks which in turn are less effective compared to N95 respirators – which have >95 per cent filtering efficiency of 0.3um particles (COVID-19 size range from 0.06 – 0.14um[CD1] [Rt2] ).
Cloth face masks
This type of face mask is not as effective compared to surgical face masks in protecting against the aerosolised COVID-19. It has however been encouraged (e.g. USA) or required (e.g. Singapore) to be worn when in the public space – especially where social distancing is a challenge (e.g. grocery stores and pharmacies) and in places where there has been significant community-based transmission reported. Their growing popularity appears to arise from the current shortage of surgical masks and N95 respirators required by healthcare workers; they are also cheaper, not difficult to make and may also be fashionable by some.
A study of common household materials used to make this type of face mask revealed that they have varying ability to block microbial aerosols; all had lower filtration efficiency compared to commercially made surgical masks and pillowcase and 100 per cent cotton were the most suitable materials in terms of their filtration efficiency, comfort and fitting (see Table 1)
Table 1 – Filtration Efficiency and Pressure Drop across common household fabrics
(Davies, A, Thompson, K, Giri, K, Kafatos, G, Walker, J & Bennett, A (2013)
According to the Food and Drug Administration (or FDA) in the USA, they are loose-fitting and disposable devices made with different thicknesses to prevent contact with liquids, microbials and particulate matter; they are regulated under 21CFR 878.4040 in the USA and as a medical device (i.e used in the diagnosis of diseases/conditions, cure, mitigation, treatment or prevention of disease), must demonstrate the following performance characteristics and identification – see Table 2 as an example.
Table 2 – Protection Levels with ASTM rated medical masks (source: Are there different levels of protection with ASTM-rated medical masks?, Pri-Med Medical Products, Inc.)
Surgical masks, compared to cloth face masks are more effective in preventing infection of influenza-like illness (ILI) as evidenced in clinical settings; however, the department of health, Australia, advise they will not benefit most people but only those who are sick, in preventing coughing on others, and also for healthcare workers who are in frequent close contact with sick persons. The CDC in the USA recommends the use of cloth face masks to slow the spread of COVID-19.
The difference between surgical face mask and N95 respirator characteristics and effectiveness are shown in the following Table 3 below :
Table 3 – Difference between Surgical and N95 Respirators (source: Center for Disease Control)
N95 respirator masks are further categorised depending if they are to be used for surgical activities or requiring a sterile environment as shown in Fig. 1 below illustrated by 3M:
Surgical N95 respirators as opposed to the standard N95 respirators, approved by both the NIOSH and cleared by the FDA, are only required in activities where there is potential exposure of high-pressure streams of bodily fluid or work in a sterile environment.
Figure 1 - Surgical N95 vs Standard N95 (Source: 3M Technical Bulletin, Surgical N95 vs Standard N95 – Which to Consider, March 2020, Rev 2)
Effectiveness of N95 respirators
N95 respirators have filtration efficiencies of >95 per cent for particles the size of 0.3um; however, they are more efficient between filtering particles between 0.04 – 0.1um (COVID-19 size range from 0.06 – 0.14um) as shown in the following figure 2 of six different types of N95 facepiece respirators tested by 3M.
Figure 2 – Averaged Filtration Efficiency for Six N95 Respirators* (on the left) and Size Distribution of Droplet Nuclei from a Sneeze (on the right) (source: 3M Personal Safety Division, Technical Data Bulletin #174, Feb 2020 Release 3). Data generated 2006
Equivalent Standards for N95 respirators
N95 respirator is the NIOSH (USA) approved product class of respirator allowed by the CDC to be used by healthcare workers subjected to aerosol generating procedures (AGP) that trigger coughing and promote the generation of aerosols. Exhalation valve models of N95 are not allowed in sterile environment to avert contamination. Owing to the global shortage of this type of respiratory protection for their healthcare workers, the CDC on the 29th Feb 2020, published a list of foreign equivalent to their N95 respirator standard which the workers may use – see Table 4 below:
From the table above, the widely used P2 respirators in Australia are therefore the equivalent of their CDC approved N95 respirators.
Can face masks and respirators be reused after disinfection?
There has not been any evidence confirming that face masks and respirators can be reused upon disinfection. However, a recent Stanford University study has suggested three promising disinfection methods in extending the lifespan of N95 respirators: hot air (75degC, 30min), UV light (254nm, 8W, 30min) and steam (10min) as shown in Table 5. Of the three modes, hot air appears to be the best option as filtration efficiency after 20 cycles was not compromised.
Table 5 – Disinfection mode against two types of filters (source: Cui, Y., Liao, L., Xiao, W., Yu, X., Wang, H., Zhao, M., Wang, Q., Chu, S (2020). Can N95 facial masks be used after disinfection? And for how many times?)