This September, the weather here has been hot, humid, sultry. A few days ago, I spied a young boy stepping down from a yellow school bus with a dark black mask hung rudely on his face at a haughty angle so that he could talk to his friends. And I wondered if he knew or cared about the danger of the thing as his hands kept adjusting its surface about his nose.
Through the Board of Education, his school now requires such a cloth mask so as to meet the dictates of the state and local health officials. Perhaps if they knew of other means of limiting infection, they would rescind such an order. Perhaps.
So quietly, rather than the challenge of public exhortation at meetings, I sent a letter to the Chairman of the Board of Education and her erstwhile opposition imploring them to consider alternatives while documenting the harm that cloth masks can cause. No answer yet..
Dear Chairman Carter,
The development of the covid pandemic, both last year and this, has interrupted the education of our children. In person education is necessary because peer-to-peer learning is an important part of the teaching process. Yet you must provide for the safety of the children and the staff.
Having served on a Board of Education in another state, I have seen how a school can be overridden by viral infection that it then broadcasts to the community. When a viral infection starts to spread within a school, the school can enter a bubble to protect the children and staff. The Principal, under the direction of the Superintendent, can restrict entry to the school by refusing entry to those who are ill. For visitors and staff, that illness test is straightforward by measuring temperature, as is currently done in local hospitals and doctor’s offices.
Children can be screened by temperature as well, but frequently will also show other symptoms such as sneezing, coughing, or runny noses. And entry to the school includes entry to the school bus as well. This requires not only a bus driver but also a bus monitor to measure the temperature and condition of incoming students. And the signed acknowledgement of the parents or guardian that the child may return home if actively ill.
For use with the SARS-CoV-2 virus where long term isolation is recommended, the school would also need to maintain a system of identification and notification so both the administration and the student or staff member would know when they can return. Contact tracing and quarantine rules also need to be determined.
To first order, that leaves those children who become ill at school during the day. The school nurse needs to be able to isolate the child until the parents or guardian can pick the child up. Or the child will need to be returned home singly by a driver and monitor, remembering that a child cannot be returned to an empty home.
The use of viral tests for restriction of entry is limited due to time constraints in processing, but could be used by the school nurse in situ. However consistent information on these tests is difficult to obtain; the CDC is continually updating test information. Even a positive test does not necessarily mean a person is infectious. Asymptomatic individuals are not likely to infect others, possibly due to lower viral load.[1]
Such a bubble system requires coordination by the administration, including additional part time workers. And, for legal reasons, the formal policy needs to be established at the Board of Education and needs to include parental notification.
In summary, a bubble system around a school can reduce the transmission of the virus into the community and can be extended to the entire educational facility if needed.
Cloth masks, on the other hand, are poorly designed to prevent the transfer of infection, and can provide an active surface for bacterial and fungal growth. Cloth masks are ubiquitous in the semiconductor industry, being part of the bunny suit that workers are required to wear in the clean rooms that are the heart of the manufacturing facilities. As a consequence, the properties of cloth masks have been studied in detail. For part of my career, I worked at IBM in that industry as a physicist, so I will write from that perspective.
A semiconductor clean room is maintained at about 45% relative humidity to avoid electrostatic discharge and condensation. Even at that mid humidity level, the hoods with cloth masks need to be replaced by the shift point (8 hours) because the masks build up bacterial and fungal growth. The workers in the clean room wear gloves and do not touch the surface of the mask because that would spread the bacterial and fungal growth. Further, the discarded cloth masks must be cleaned in a specific way using UV light or specific detergents in order to be reused. [2, 3]
At higher relative humidity, the operative use time of cloth masks is reduced. The Board of Education should direct the Superintendent to establish acceptable micro biotic exposure and mask replacement times based on measurements of relative humidity, air flow, HVAC filtration, building pressure, and temperature. The replacement procedure should be documented. The administration would also need to provide all students and staff with the cloth masks in order to maintain the quality and reusability in the way that some hospitals do now.
Moreover, cloth masks do transmit small aerosols. Epidemiologists have determined that a virus can be transmitted by aerosols (liquid particles), so mapping the response of cloth masks to particle size is necessary to determine their functional limitations. The SARS-CoV-2 virus is about 100 nm, so a liquid aerosol containing a virus with be slightly larger. Note that small aerosols, below 5 µm, are not visible to the naked eye and diffuse by Brownian motion like invisible dust mots.
For reference, N95 masks as used in hospitals filter 95% of the aerosols down to 0.3 µm, 300nm, or about the size of aerosol that can contain a single virus resulting in 5% transmission. The original tests published by the National Institute of Health even went to 0.1 µm, and included a good face seal. [4]
Aerosols in clean rooms can be measured as the worker moves past the detector. Typically, the best measurements of sub-micron airborne aerosols use a Condensation Nucleus Counter (CNC). The distribution of aerosol size varies by a power law:
p(x)=Ax^α
where α is typically -3 ± 0.3. These measurements led to the setting of ISO standards for clean room classification on the high side of that power law down to 0.1 µm. [5, 6, 7]
From this distribution, we can calculate the volume of liquid aerosols as a function of aerosol size, a measure of the viral carrying capacity. Thus, we see that sub-micron particles carry as much material as their larger visible counterparts because their number increases as fast as their size goes down.
The transmission of aerosols through cloth masks has been measured to be greater than 90% because the pore size of the mask did not restrict sub-micron particles. [8, 9] Recently, a meta study looking at transmission data for cloth masks reported 60-98% transmission, with the increase in filtering achieved thru multiple layers and electrostatic interaction.[10]
Of course, all of the transmission measurements assume a tight fit of the mask to the face of the wearer. In a community environment like a school with small children, that is not very likely.
In summary, cloth masks do not prevent the transmission of viral infection, and their use in a humid environment and without proper handling can cause harm. You cannot expect children to use the proper protocol.
I apologize for the length of this letter, but I needed to suggest a positive approach to protection, a bubble system, while delineating an ineffective and harmful approach, cloth masks. Thank you for your consideration.
Sincerely,
John Mauer
References:
1. [https://pubmed.ncbi.nlm.nih.gov/33219229/]
2. [Clean room standards IEST: https://www.iest.org/Standards-RPs/Recommended-Practices/IEST-RP-CC003]
3. [Reusable Cleanroom Garments: https://sst.semiconductor-digest.com/2006/02/reusable-cleanroom-garments-part-1/]
4. [https://pubmed.ncbi.nlm.nih.gov/9487666/]
5. [ISO Standards: https://www.clean-rooms.org/iso-cleanroom-standards/ ]
6. [C.H. Stapper et al. IBM J. RES. DEVELOP. Vol. 24 No. 3 May 1980]
7. [Donovan R.P., Locke B.R., Ensor D.S. (1988) Measuring Aerosol Particle Concentration in Clean Rooms and Particle areal Density on Silicon Wafer Surfaces. In: Mittal K.L. (eds) Particles on Surfaces 1. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-9531-1_4]
8. G. S. Settles, G. G. Via, “Measurement and Control of Particle-Bearing Air Currents in a Vertical Laminar Flow Clean Room”, In: Mittal K.L. (eds) Particles in Gases and Liquids 1. Springer, Boston, MA. https://doi.org/10.1007/978-1-4613-0793-8_12
9. G. Sullivan & J. Trimble, “Evaluation of face coverings”, Microcontamination, 4, No. 5 64-70 (1986)
10. Suresh K. Sharma et al., “Efficacy of cloth face mask in prevention of novel coronavirus infection transmission: A systematic review and meta-analysis”, J Educ Health Promot. 2020; 9: 192, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7497125/#
A Man may make a Remark –
In itself – a quiet thing
That may furnish the Fuse unto a Spark
In dormant nature – lain –
Let us divide – with skill –
Let us discourse – with care –
Powder exists in Charcoal –
Before it exists in Fire –
Emily Dickinson