On face masks, vaccines and hard borders: a Jarlsberg cheese theory of risk management

Before you read on: this post is not about debating whether COVID-19 exists, or whether vaccination mandates are needed, or the validity of various rules. You have plenty of other places to share those opinions; kindly do that elsewhere.

This is about risk management and understanding probability through one of my favourite things:

Cheese.

I didn't come up with this explanation.

It's a common approach used in occupational health and safety.

This is how risk management is often taught on operating sites where things can kill you, like refineries, smelters, processing plants and concentrators.

It's how I learned about risk before I became a facilitator for Hazard and Operability studies (HAZOPs), Workplace Risk Assessment and Control (WRACs), Process Hazard Analysis (PHA), Root Cause Analysis (RCA), Failure Modes and Effects Analysis (FMEA), Bow Tie diagrams... you get the picture, I've done a lot of work in the risk reduction and management space in my engineering career.

With all of that training and experience, I still like the Jarlsberg (a.k.a Swiss) cheese explanation best when I'm explaining risk to others.

It might be useful to you, too :)

Step 1: Define the risk that could affect you

You are exposed to things that can harm or kill you every day.

Getting in a car is a prime example. It's the riskiest thing most people do, because the potential harm from a car accident is so high. It's also acute - people who die from car accidents tend to die quickly because of the nature of their injuries.

Breathing polluted air is another example. It's a chronic risk, because the negative effects build up over time and it can take many decades to kill you, but it's still a risk.

Step 1 is define your relationship to the risk, like this:

Step 2: Put controls in place to stop the risk reaching you

Ideally, we want to prevent avoidable risks reaching us. Prevention is better than cure, right?

There are broadly five categories of prevention controls you can use:

(image source: https://en.wikipedia.org/wiki/Hierarchy_of_hazard_controls)

As you can see, elimination is the most effective.

Now we get to the Jarlsberg:

Imagine each control strategy is a slice of cheese you put between you and the risk. If the risk hits cheese, it doesn't get to you. If the risk hits a hole, it comes closer to reaching you.

Elimination is like a solid slice of cheese with no holes in it. It stops the risk, like this:

One elimination step is worth hundreds of substitution controls, engineering controls, admin controls or personal protective equipment options because one elimination step removes the need to do all the rest - the risk is not longer able to affect you.

Step 3: If you can't eliminate, move down the hierarchy

Not all risks can be eliminated.

Sometimes we need less effective controls than we'd like.

A good control is as solid as possible - it's got just one or two Jarlsberg holes, and they're very small.

A poor control has lots of holes, so the probability of the control working is low - but that doesn't mean you don't do it (more on that later).

Everything that's not elimination cannot be 100% effective in preventing that risk reaching you.

At some point, the risk hits a hole in the cheese and passes right through that control, so the risk reaches you:

The aim of the risk reduction game then becomes:

• Put multiple controls (Jarlsberg slices) between you and the risk
• Find as many Jarlsberg slices with mostly solid cheese as you can (i.e. controls that are as as effective as possible)
• Don't forgo any slice of cheese you deem worth it - every slice will reduce your risk, even if it's only by a fraction.

The risk can still get to you, like this example with six non-elimination controls in place:

...but you're hoping that it will hit the solid part of at least one of those six slices and not reach you.

It's all a game a probability at that point.

But, and this is crucial: it's still better to have some protection in place if you believe the risk is one you want to avoid.

What's that got to do with vaccines, face masks and hard borders?

They're all control strategies for reducing the risk of you catching COVID-19 - they're slices of Jarlsberg between you and that risk.

If you were going to put them on the hierarchy of control, WA's hard border was as close to elimination as you were likely to get - though definitely not impenetrable.

Vaccines are something like engineering solutions, and face masks are the definition of personal protective equipment.

The ratio of open holes to solid cheese in the Jarlsberg slice differs, and how you manage those controls personally affects that ratio.

Here's an illustrative example:

We can argue about the ratio of holes-to-cheese of any given control as long as we like.

I will personally only take the word of scientific researchers as to what those ratios are for health-related controls.

But, and here's the really important point:

Anyone who says a single control 'doesn't work' is flat-out wrong if it works at least occasionally, or to some degree.

It's about how effective the control is.

Even if that control only works one time in 100, or it only reduces your chances of the risk reaching you by 1%, it still provides some protection.

100 control strategies that are just 1% effective makes your total chances of the risk hitting you 36.6% (99% ^ 100). That's a 63.4% chance it won't hit you. Better than a 100% chance that it will, if you're trying to avoid that risk.

What does that mean for you?

If you'd like to reduce your chances of catching COVID-19, or you'd like to reduce the number of times you'd like to catch it, think about the layers of Jarlsberg sitting between you and the virus.

(If you're not worried about catching COVID-19 and/or you're fine with catching it multiple times, you can stop reading now.)

How many slices of Jarlsberg have you got? Examples include safe spacing, isolating, good hygiene like washing hands properly and not touching your face, eating healthy, exercising, wearing a mask, getting vaccinated.

How effective are they, in your case? For example, if you chose safe spacing, how often does your 1.5m limit get breached, and for how long? If you're wearing a mask, is it properly fitted and worn the right way?

And now, for the really tricky question:

What does that mean for your community?

The models that look at spread of the virus depend on the % effectiveness of control measures.

You've only got to look at what's happened in NSW since mask restrictions were removed recently to see how quickly the spread accelerates when a piece of Jarlsberg disappears.

The more effective your controls are, the fewer people you'll spread COVID-19 to.

It's that simple.

As I've said already, there are plenty of other places you can vent about mandates and how serious the disease is if you so choose, so if you're about to start down that path, best to head elsewhere :)