Thread by @thebencheah

I'm seeing Twitter personalities urging readers to wear masks to protect themselves from #Covid_19. I'm sure they mean well, but how effective are masks, really?

Let's explore this topic from the perspective of Occupational Health and Safety (OHS).

/1

In my day job, I draft, among other things, OHS manuals and procedures. These include instructions to control workplace hazards, including infectious disease.

I am NOT a certified ISO / OHSAS professional, but you learn a lot from osmosis, including the hierarchy of control. /2

The hierarchy of control describes measures to control risks. In order of most to least effective, they are:

1. Elimination
2. Substitution
3. Engineering Controls
4. Administrative Controls
5. Personal Protective Equipment

There's a reason #PPE, including masks, is last. /3

At the PPE stage, the person is placed in contact with the hazard.

The success of PPE controls depends on many factors: right fit, proper maintenance, training, correct use, etc.

It relies heavily on imperfect humans.

It supplements, but DOES NOT REPLACE, other measures. /4

Elimination completely removes exposure to the hazard.

In the case of the #coronavirus, this means quarantine, lockdowns, and staying far away from mass gatherings.

You cannot get sick if you do not come into contact with the virus.

/5

Substitution involves substituting a product or process with something less hazardous.

Teleworking is one example. People can still go to work without exposing themselves to disease.

Same for homeschooling.

As above, you can't get sick if you don't encounter a spreader. /6

Engineering controls means using physical means to reduce the likelihood of occurrence or severity of consequences.

Isolation wards, blocking off tables at restaurants, air filters and other measures.

People are still in proximity to each other, but the risk is reduced. /7

Administrative controls reduce exposure to a hazard by getting people to obey instructions.

Now you know why the government and the media reiterates the same message every hour: #WashYourHands, #StayAtHome, etc.

But this relies on people actually following instructions. /8

Elimination and substitution aim to ELIMINATE exposure to hazard.

Engineering and administrative controls try to REDUCE exposure.

PPE merely tries to MITIGATE the consequences of exposure.

In other words: wearing masks is the LEAST effective method of protection.

/9

Twitter personalities say, "Studies show masks reduce the spread of disease!"

Yes, they do.

But they fail to account for the above-mentioned factors.

The truth is, we don't know how effective masks truly are in everyday situations.

/10

The majority of studies focus on the following:

-Healthcare personnel (HCP) attending to patients
-Patients
-Caregivers of patients at home

These situations require close prolonged contact (over 30 minutes, less than 2 metres), making it easy to catch a virus. /11

HCP wear masks AND goggles AND gloves AND full-body PPE.

AND adhere to all the OTHER means of hazard control above.

Done properly, this completely eliminates their risk of catching the virus.

This is because they maintain a multi-layered defence. Not just PPE. /12

HCP do need #PPE urgently. They cannot eliminate exposure to the virus. They MUST have PPE, but there is a global #PPEshortage.

Yet understand that masks are only one component of PPE, and PPE is itself integrated into a wider set of protocols.

Do not fixate on masks. /13

Studies report that patients who wear masks may reduce the virus particles they shed in every cough or sneeze by up to 95%.

Naturally, this means they are far less likely to spread disease if they wear masks.

That means confirmed patients have second priority for masks.

/14

Caregivers are less likely to catch the virus if they wear masks.

This likelihood is further reduced by exercising proper hygiene, including washing hands, and IF the patient ALSO wears a mask.

(See above, Hierarchy of Control and multilayered defence.)

/15

What about transient contact, such as on public transport, in a car, on the street, etc.?

We don't know.

There is insufficient data on the usefulness of masks in open spaces against transient contact with potential viruses.

With that said...

/16

If you wear a mask and go to places that facilitate the spread of disease, you are willfully violating the first four control measures.

You are ignoring the more effective control measures in favour of the least.

Your mask won't save you from stupidity. /17

A mask may block SOME virus particles.

However, even if it blocks 100% of virus particles (which, unless it is an N95 or better respirator fitted to your face, it can't), you're still not fully protected.

#Covid19 spreads through the eyes. Masks don't cover eyes.

/18

Can a mask alone block enough virus particles to prevent the virus from overloading your immune system?

We don't know.

Thus, if you are not in full-body PPE, with goggles and mask and suit and gloves, if a #Covid_19 patient coughs on you, assume you'll get it.

/19

If your job does not require you to come into contact with the virus, why risk it?

PPE is imperfect. A mask alone may not be enough.

But if you organize your life to eliminate, reduce and mitigate exposure to the virus, you won't need the mask. (Usually.)

/20

What does this mean?

#StayHomeStaySafe

#WashYourHands

#DontTouchYourFace

If you don't leave an opening for the virus to enter your life, you won't contract it.

PPE -- i.e. a mask -- is your last resort, to supplement all other measures. NOT replace them.

/21

But if your job is to go into the plague zones, care for the sick, or otherwise carry out the vital work of keeping civilization going:

Good luck, God bless, and stay safe.

This pandemic is a long way from being over. We all have to do our part.

/end