COVID-19: TYPES OF MASKS AND FACE COVERINGS

In an earlier blogpost, we looked at the science behind the value of the general public wearing masks or face coverings.  In this blogpost we look at the various types available.

In that blogpost we saw that the main route of transmission of this dangerous COVID-19 disease is now believed to be viruses in the microdroplet "aerosols" that we all breathe out when we talk, sing, shout, cough or sneeze.  A mask can catch aerosols and larger droplets, and thereby reduce transmission dramatically.  On that basis the general principle is that:
"My mask protects you.  Yours protects me."

This principle is important, as a significant proportion of people who test positive for COVID-19 and are infectious don't know it, because either they are:

• "Asymptomatic", and never display the basis symptoms.  This can be over 50% of the positive tests
• "Presymptomatic" before they display symptoms, typically for 5 days (in range 2-14 days), when they can be more infectious than when they have developed symptoms

So everybody who does not have COVID-19, even if they have recovered, is capable of having the virus and of being infectious without knowing it.  If they are, wearing a mask helps stop them infecting others.  That's why it is worth everybody wearing a mask or face covering, at least indoors.


TYPES OF FACE MASKS

There are fundamentally two types of face masks and face coverings:

• "Respirator" masks primarily designed to protect the wearer, with the critical airflow direction being inhalation outside to inside.  These are used by front line health workers as part of their PPE (Personal Protective Equipment).   Protection for these workers is important, given they are working with patients who are coughing and generally filling the air with aerosols full of viruses

• "Source control" masks primarily designed for exhalation to catch aerosols and bigger droplets, commonly referred to as "masks" or "face coverings".  Their purpose is for the general public, as above, that "My mask protects you.  Yours protects me".  They include "surgical masks" and "medical masks".

But the thought arises, which masks for the general public provide:

• Best protection against infecting other people?
• Also provide the best personal protection? 

MASKS TYPES IN MORE DETAIL


Personal Protective Equipment (PPE)

PPE has generally been in short supply, and so the general public has been asked not to buy such items and divert away from frontline workers.

However that situation is beginning to ease, and if you are one of those people who have been shielding because you are especially at risk of serious COVID-19 symptoms, PPE is worth considering.

For masks, this summary for Dental Nurses explains:

• N95 masks is a general term meaning No oil resistance, and will stop inhalation of 95% or more of suspended particles
• The equivalent in modern standards are FFP2 face masks which are held in place by ear loops and have a lifespan of 3-8 hours depending on environmental factors. 
• FF3 face masks offer greater protection, and have a valve as the material is thicker.  These masks are typically used by people handling asbestos.  

Typical visor

Front line workers who have to work in close proximity to patients also use visors as PPE.  These stop direct splashes from patients coughing, sneezing or spitting droplets.

Typically there is a thick band on the forehead so people can wear glasses.  A problem is there is a large gap around the sides, which lets aerosols in to the wearer's face.  However visors will deflect many of the aerosols when someone is talking directly to you, and so provide more protection than not wearing a visor.

The gaps around the sides also mean aerosols escape from someone infectious, and so a mask should always be worn underneath to catch aerosols.

Indeed both visor and Type II masks  (as described below) are required to be worn by barbers, hairdressers and other personnel working in close proximity to their clients to:

• Reduce risk of worker catching COVID-19 from a client, especially when working in front of the client's face
• Reduce risk of worker infecting their client

For the General Public 

This advert taken from a national newspaper describes the different types of masks and visors :

On the left of the advert is a type of "surgical mask", known as a "Type II face mask" complying with the EN14683 standard .  This type of mask is made up of a protective 3 ply construction that prevents large particles such as bacteria from reaching the patient or working surfaces.  It will also stop many of the aerosol droplets, though 'naked' viruses are very small and will get through.

They are often marked as having a BFE of over 95%, but as this stands for "Bacterial Filtration Efficiency", this is irrelevant for COVID-19 purposes.  Indeed Boots says "The use of face masks does not provide protection against coronavirus (COVID-19) but could help to minimise the risk of transmission to other people in some circumstances."

Here are two brands currently on sale in Boots, both certified to EN14683:

• One has elasticated straps, which allow it to be dropped carefully below the chin when you're away from other people
• The other "Medical Face Mask" has fixed straps, and a tighter fit.  

They typically cost less than a pound each, but as they need to be disposed after a single use, that can be a significant expense for some people.

As Boots says, "Face masks should not be used in place of social distancing and hand washing, or in place of self-isolation. Anyone with coronavirus (COVID-19) symptoms, and their household, must still self-isolate at home."

Reusable, washable face masks are becoming available from a host of sources, with a range of designs.

Sizes are available for adults and children.

There is a wide range available from small producers on Etsy.


Look out for masks that have:

• Three layers
• Pocket for kitchen roll, to improve ability to catch water droplets

Vented masks should be avoided, as the vent doesn't stop aerosols escaping to potentially infect other people.

Indeed the FF3 face masks mentioned above are designed to protect the wearer, and the valve specifically lets breath out which could be laden with coronaviruses


There are various ways you can make a 'face covering' at home, preferably with three layers of fabric and a pocket for a kitchen towel as a cheaper alternative to buying one.  It must cover the mouth and nose, and be as snugly fitting as possible to avoid microdroplets escaping from the sides.

Here are some suggestions as to how to make one at home:

• From the American Center for Disease and Infection Control (CDC).
• From the UK government, if you like sewing
• Three designs from the BBC

Which? have produced an extensive guide on buying and making masks, including tips about avoiding scams.


EFFECTIVENESS OF MASK TYPES FOR SOURCE CONTROL

There are a whole host of studies that either took place before the COVID-19 pandemic, or focus on how well the PPE types work to protect the wearer.  There are very few addressing the effectiveness of Source Control masks for the general public.

Here's a new study from Duke university in the USA which specifically assesses how effective various masks are when the wearer talks.  Even the simplest types were effective.  Unfortunately three-layer masks weren't included, but otherwise disposable Surgical Masks were the most effective of those avai;able to the general public:

EFFECTIVENESS OF MASKS TO PROTECT THE WEARER

This trial did not attempt to assess how effective each type of mask would be in protecting the wearer, but we can imagine:

• Whether the masks stop droplets and aerosols coming in will be similar to going out
• Once droplets and aerosols bearing viruses have landed on the masks, the viruses are likely to be breathed through and into the respiratory tract, unless of an N95 type.

This study suggests that wearing a mask can reduce the 'viral dose' a person receives, which in turn reduces the 'viral load' in the body.  That makes it easier for the immune system to cope, and a milder infection can result.

It is estimated that surgical masks can reduce risk of infection by some 30%.



USE OF VISORS

As noted above, a visor will also provide some protection to the wearer.

But must always be worn with a mask unless the person has a specific exemption.








SO WHAT TYPE OF MASK SHOULD WE USE?  WHAT WILL PROTECT US BEST?

Disposable three-ply Surgical Masks that are made to an exacting EN14683 standard have been shown to work best for Source Control for exhalation.  They effectively stop aerosols that would otherwise infect other people if the wearer is infectious.  Surgical Masks are likely to work best for inhalation too, to provide at least some protection to the wearer.

So I will continue to wear Surgical Masks until a better solution is proven.

But the choice is yours.  Anything is better than nothing, though preferably three-ply construction and avoiding vents.