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

Writing this in the middle(?) of the coronavirus outbreak I thought it might be interesting to share these charts, created from the simulations in the excellent Washington Post article “Why outbreaks like the coronavirus spread exponentially, and how to ‘flatten the curve’” by Harry Stevens.

The charts represent different strategies for containment and mitigation of the effects of a contagious outbreak.

Trying to quarantine an area — where it is difficult to attain complete quarantine — delays the effect of an outbreak somewhat, but once released the impact is still significant with a potentially high peak of cases.

Social-distancing — staying away from each other to reduce the chance of infecting others if you are infected and minimise the chance of infecting yourself — in both the bottom scenarios in the simulation manages to both delay the onset of an outbreak and reduce the peak. Not included in this simple simulation is that reducing peak infections in particular helps the healthcare system effectively treat and care for those who are infected, and look after its healthcare workers. When healthcare is not overwhelmed this further minimises both the spread of a disease and fatality rate.

Read the article, run your own simulations, and maybe consider supporting the Washington Post, here: “Why outbreaks like the coronavirus spread exponentially, and how to 'flatten the curve’”.

Disclaimer: I am not a public health professional. These charts are from my results of the simulations in the article and the simulations represent a simplified, though instructive I think, view of an outbreak and these containment methods.

Flatten the curve of an outbreak

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…

Dry your hands with only one towel. And as a basic rule…

The handwashing guidance is from the wonderful NHS.

How to wash your hands

I was taught this originally for backpacking but it really always makes sense once you think about it. Pouring onto a hand keeps dirty hands out of the rest of the snacks in much the same way as a drinking fountain manages to be hygienic by shooting out the water.

Some alternative sides to sharing: compliments are gifts and give gifts others can give. And two more about germs: sneezes and coughs, and the Dracula sneeze.

Pour, don’t dip when sharing snacks.

‘Tis the season for these powerful things. Turns out sneezes can travel up to 8 m, coughs up to 6m and they can linger in the air for up to 10 minutes.

All the more important to make sure you’re doing your Dracula sneeze into your sleeve.

Sneezes and coughs

A Dracula sneeze is sneezing into your sleeve at your elbow rather than sneezing into your hands.

The dramatic full Dracula pose is a fun reminder of a more hygienic way to sneeze should you be caught without a tissue. Keeping your hands clean by catching sneezes or coughs in this way helps reduce the chance of spreading cold and flu germs.

However, the CDC’s preferred method for coughing and sneezing is to cover your mouth and nose with a tissue, throw it in the trash and wash your hands.

Dracula sneeze

If you are feeling the need to sneeze some people will find that looking at a bright light can help release it.

Apparently, it’s called the photic sneeze. I asked the question of Focus magazine in the UK, and it seemed to me that Science doesn’t really know why. We need to find out.

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Category: germs