The Swiss Cheese Model helps explain why, despite all our best intentions, accidents happen.

Analysis of accidents in large complex systems such as power stations or plane crashes led to an understanding that "no one failure, human or technical, is sufficient to cause an accident. Rather, it involves the unlikely and often unforeseeable conjunction of several contributing factors arising from different levels of the system."

James Reason's Swiss Cheese Model is a memorable visual metaphor that illustrates how each safeguard may contain a latent flaw or hole and that an unfortunate circumstance may result in these holes lining up to disastrous effect. It's also a nice reminder that multiple layers of defence will be more effective, but even with our best efforts, there's still potential for something to go wrong.

Excerpt from Revisiting the "Swiss Cheese" Model of Accidents (pdf), Reason, Hollnagel and Paries, 2006.

Coronavirus example from the Cleveland Clinic.

I learned recently that it's sometimes called the "cumulative act effect".

This sketch, updated and polished, features with a number of others in my book Big Ideas Little Pictures.

The Swiss Cheese Model

In these times, and to be honest, most times, washing your hands well is one of the very best things you can do to keep yourself healthy and free from infections.

You should use soap if you have it; it should take about 20s, and if you follow these steps, you’ll cover pretty much all of the different parts of your hands. In standard, cursory handwashing, it’s very easy to miss what ought to be obvious places to clean, like your fingertips. Then, try to avoid touching taps and door handles on your way out of public places.

I find doing these steps takes about 20s, but to make sure you could also try singing a song segment you like. NPR has some suggestions: Keep flu at bay with a song.

Some other hygiene sketches to bear in mind:

Sneezes and coughs are powerful things — a sneeze can travel up to 8m. So always make sure you do your…

And as a basic rule…pour don’t dip when sharing snacks

The handwashing guidance is from the wonderful NHS.

How to wash your hands

Learned from Joe Smith’s short entertaining TED talk: How to use a paper towel.

Washing sketches