Corona Daily 214: The Swiss Cheese Model

Joe Biden wears two masks, a surgical mask over an N95 mask. It is not to compensate for the outgoing president who doesn’t wear any.

Layering two less specialized masks over each other can provide protection comparable to the N95 masks. It is recommended that face shields must be used with a mask. Though the clear plastic shield is impermeable, air seeps out and comes in around the edges. Each additional layer makes it difficult for the virus to get in or out of the nose and mouth.

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Dr James Reason, a British cognitive psychologist and professor, first introduced the Swiss Cheese concept in his 1990 book called “Human Error”. A series of disasters in the previous decade including the catastrophic accidents in Chernobyl, Bhopal and the Challenger shuttle explosion motivated the analogy.

In the Swiss cheese model, an organisation’s defences against accidents or failures are modeled as a series of slices of Swiss cheese with holes known as “eyes”. Holes in every slice represent a weakness of that individual slice. The slices have holes in different positions. The system produces failures when a hole in each slice momentarily aligns, permitting “a trajectory of accident opportunity”, says Dr Reason. When the danger passes through holes in all of the slices, it results in a failure, sometimes catastrophes.

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Even without reading Dr Reason’s book, we usually know examples of the implementation of multi-layered protection.

Take Google’s 2-step verification. When we want to recover the forgotten Gmail password, Google may want to send an email plus a code to our phone. Despite using our login and password, our bank may send us an OTP before we can carry out a transaction.

There is always a balance to be struck between convenience and safety. Google can, of course, make it a 5-step verification to make it hacker-proof, but we may get sick and stop using Gmail. Wearing three or four masks one on top of another will certainly offer better protection, but we risk dying of suffocation before the virus can strike.

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Another good example is our crossing the road, particularly in places like Bombay with speeding bikes, narrow or absent pavements, and shaky road discipline. We look both ways, cross when the pedestrian light is green, continue to keep a wary eye on traffic as we cross, avoid the temptation of looking at our smartphone. Though it may be impossible to eliminate the risk, each of these precautions reduces the risk drastically.

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Avoiding getting infected, hospitalized or dying by the coronavirus is similar to avoiding getting hit by the car when crossing the road.

No single layer is perfect, each has holes. When several holes align, the risk of infection increases. When multiple layers are combined – social distancing, plus masks, plus handwashing with soap, plus testing and tracing, plus ventilation, plus strong government messaging plus vaccines - multiple fencing reduces overall risk. People who think vaccines offer a magic bullet may be wrong. Vaccination is simply one of the cheese slices.

A coronavirus sceptic is called the “misinformation mouse”. Such people will confidently tell you about the uselessness of masks, or the impracticality of contact tracing. Without being experts, they confidently and loudly start making new holes for the virus to pass through.

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Until the pandemic ends, all of us, and particularly those in the vulnerable categories, will benefit by remembering the Swiss cheese model.

Ravi