Sunday Times 2
Cloth facemasks – a brief overview
A droplet with particle diameter of >5 µm is referred to as a respiratory droplet. A droplet with particle diameter of <5 µm are referred as droplet nuclei. Droplets can be transferred through close range contact. Droplet nuclei can be airborne and travel significant distances.
By Dr Aseni Wickramatillake, Artha Salgado, and Dr Changa Kurukularatne
The threat
According to the World Health Organisation (WHO), SARS-CoV-2, the virus responsible for COVID-19, is transmitted through droplets when sneezing, coughing or talking, and through physical contact with contaminated surfaces. The carrying distance of a droplet through the air is dependent on the velocity of the expelled air, and varies from a distance of 1 metre up to 6 metres depending on the mode of expelled air. Large droplets are carried over 6 metres by sneezing (velocity 50 meters per second), over 2 metres by coughing (velocity 10 mps), and up to 1 metre when talking or breathing (velocity 1 mps)
Cloth masks – how they work
Two-ply face-masks have an outer waterproof layer and an inner absorbent layer, typically made of cotton. Three-ply face-masks have an additional middle filter layer.
Droplets from the outside environment are prevented from entering the wearer’s nose and mouth through the water-resistant outer layer. The inner absorbent layer absorbs moisture secreted or expelled by the wearer. The outer layer also prevents droplets from the wearer being expelled into the environment.
Cloth masks – variables
The following features and properties should be considered when choosing a face-mask.
- Numbers of layers of fabric/tissue
- Breathability of material
- Water repellence/hydrophobic qualities
- Shape of mask
- Fit of mask
- The ability to be machine-washed and dried without compromising material integrity or configuration over repeated wash/dry cycles
Cloth masks – uses and limitations
A cloth face-mask reduces — but does not eliminate — the spread of respiratory droplets when the wearer breathes, talks, coughs or sneezes. A cloth face-mask reduces — but does not eliminate — the risk of the wearer’s mouth and nose from inhaling droplets from the external environment. Cloth face masks are not considered to be the same as surgical masks.
Cloth face coverings should not be placed on young children under age 2, anyone who has trouble breathing, or is unconscious, incapacitated or otherwise unable to remove the mask without assistance.
The increase in thread count can improve the filtration capabilities of the mask. Combining layers to form hybrid masks (with flannel, chiffon, silk) influences the mechanical and electrostatic filtering of airborne particles. The external fluid-resistant layer prevents droplet being expelled to the environment, as well as droplets from reaching the inside of the mask. The presence of gaps between the mask and facial contours will reduce the effectiveness of the mask, resulting in “air leakage” with droplets entering and exiting. A better seal can improve the filtering efficiency of any type of mask. Facial hair, especially beards, can affect the fit of the mask.
Cloth masks – concerns
(real and imagined)
SUFFOCATION: A concern among certain people is the degree and facilitation of air exchange through the mask material. Unconfirmed reports have stated that masks hinder gas exchange and cause the wearer to collapse due to lack of oxygen and increased humidity. In fact, the layers of surgical masks and cloth masks enable adequate gas exchange. This holds true even in masks with a water resistant protective outer layer. Aeration occurs via the mask itself and via the gaps along the non-fit interface between the mask edge and the wearer’s facial contours.
On the contrary, covering the head and face with polyethylene or polythene (or similar impermeable material) will hinder the transportation of oxygen and carbon dioxide, with potential for fatal outcomes.
EXERCISING WHILE WEARING A MASK: Under normal circumstances there is no concern about wearing cloth masks during exercise. The user must remember that air flow is restricted when breathing through a mask. Therefore, the user may be fatigued more easily. The body can be conditioned over time to exercise as per usual while wearing a mask. However, if you feel breathless, dizzy, lightheaded, or have numbness or tingling, stop exercising and rest, preferably laying down, and be mindful of safely resuming exercise while listening to your body. This is especially true for people with heart or lung disease, or those who are de-conditioned and are starting an exercise programme.
PUBLIC SPEAKING & WORK MEETINGS: There is some concern that the voice does not project well when speaking while wearing a face mask. The surgical mask does not pose this problem as the layers can easily transmit sound.
Some cloth masks are made of thick material or multiple layers, which is a barrier to sound transmission, but does not confer extra protection from SARS-CoV-2. Therefore, speakers at meetings have a tendency to remove or lower their mask when speaking. This is a dangerous practice, when talking, the secretions from the mouth can travel distances even greater than two metres. Protection against SARS-CoV-2 is determined by the degree of water-resistance in the outer layer and correct techniques of mask-wearing. Thick or multiple layers cause discomfort to the wearer due to increased sweating, especially in hot and humid environments.
CONTAMINATION: A surgical mask can carry the SARS-CoV-2 up to 7 days on the outer layer and 4 days on the inner layer. It can be present in cloth for up to 1 day. Hence, the mask has to be treated as a source of contamination. Donning, doffing, discarding, and temporary storage (where unavoidable) is therefore high risk steps associated with the use of face-masks.
Safe donning, doffing,
handling and cleaning
A. Wearing (donning) and removal (doffing) of masks should be done carefully to avoid cross-contamination.
B. Masks should only be touched from its loops or strings during donning and doffing.
C. Hands need to be properly washed or sanitised before and after handling a mask.
D. Avoid touching the outside or inside layers of your mask.
E. A removed mask should not be placed in pockets, tabletops or any other surface. Doing so results in cross-contamination with the virus. Used masks should always be regarded as sources of contamination.
F. A cloth mask should be washed immediately after doffing to minimise the risk of cross contamination.
G. Cloth masks should be washed thoroughly with soap and water, and thoroughly sun-dried or tumbled dried in hot setting. The filtering efficiency of a cloth mask is reduced after multiple washing cycles. Please check manufacturer recommendations regarding the number of wash-cycles a mask can withstand before material integrity is compromised.
H. If not washed immediately, masks should be placed in a clean, breathable container until ready to be washed. This container should be clearly labeled with the user’s name, and cleaned and sanitized after each use using cleaning agents with known virucidal efficacy against SARS-CoV-2.
I. Once mask has reached the end of its usable life, ensure the mask is thoroughly washed and dried prior to disposal. Alternatively, the mask must be disposed as biohazardous waste.
J. As always, reasonable common sense goes a long way in keeping ourselves safe.
Cloth face-masks – do they work?
It is challenging to prove the efficacy of cloth face-masks in the context of COVID-19 due to a variety of confounding factors and variables. However, when compared with countries that do not require public use of face-masks (or made such mandates late in the process), countries with early requirements on the public use of face-masks appear to have flatter COVID-19 epidemiology, curves even when adjusting for lockdowns.
About the Authors
Dr. Aseni Wickramatillake is a specialist in occupational health and safety, and an expert in industrial hygiene.
Mr. Artha Salgado is the Secretary of the Workplace Safety and Health Association (https://wsha.co) and practices health and safety in a regional capacity at a large multinational organisation.
Dr. Changa Kurukularatne is a specialist in infectious diseases, infection prevention and control, and an expert in outbreak response and disaster management.
Correspondence: COSHlanka@gmail.com