Swiss Cheese: It’s Bad for Your Health

Things go wrong:

  • People sleep in
  • Training isn’t acted on
  • Doors get left open
  • Staff members resent each other
  • Taps get stuck open
  • People put boxes on the wrong pile

Shit, as they say, happens.

Normally “things gone wrong” are just an irritant, a minor expense, nothing to get too worried about.  Sometimes however, it is worse than that.

There is an accident prevention idea called the “Swiss Cheese Model”.

The theory is that mistakes are like holes in a slice of swiss cheese, they happen from time to time.

Now imagine 10 slices of swiss cheese stacked together.  You can’t see all the way through because the holes are in different places.  Nothing too bad happens.  Every now and again though the holes line up, and then something that was mildly irritating becomes a big deal.  Let me give you a couple of examples:

In 1987 the Herald of Free Enterprise capsized.  193 people died.  Why?

  • The person whose job it was to close the ferry doors slept in
  • The ferry was more unstable than usual as the ballast levels had been changed to let the ferry float higher and reach a different car ramp
  • Somebody who could of closed the doors didn’t because it “wasn’t their job”

In 1996 Valujet flight 592 had an onboard fire in a fire proof cargo hold (sealed to air) and crashed into the Florida Everglades killing 110 people.  Why?

  • Somebody incorrectly stacked a cardboard box of oxygen generators when tidying up a warehouse
  • The box was placed in the hold by mistake
  • Somebody else had stuck the firing caps of the generators down with sticky tape instead of the prescribed plastic caps
  • A jolt on take off fired the oxygen generators (which also create heat when they are working).

In 1979 the nuclear power station at Three Mile Island had a partial melt down.  Why?

  • A cooling water valve stuck open
  • A warning light wasn’t set up correctly
  • An operator manually over rode a cooling system

A few minor things can have a big impact.

And the point is?

  1. We love to make things complicated and the more complicated we make things, the more likely it is that something will go wrong.
  2. We aren’t very good at fixing small issues, they aren’t worth the effort.

Assuming you don’t want to have a disaster on your hands, it is worth addressing points 1 and 2 above.  Otherwise it is just a matter of time.

Read another opinion

Image by Fumble Mouse



  1. James, you hit on a great point. Keep things simple and fix the small stuff before it becomes a big deal. The small stuff isn’t what is recognized by leaders when someone fixes it before it is a problem. Leaders need to change their mentality and praise the fix to the small stuff and not praise someone who fixes the wild fire that is out of control. The leaders need to understand what little things caused the wild fire and why those little things weren’t taken care of when they were little.

  2. Hi James,
    It is easy to recognise complexity and ignore small changes but it is harder to recognise the systemic way that things work and how they all can and do link together. Sometimes to devastating effect… the ‘Butterfly Effect’. Taking time to step back and look at the whole system can pay rich dividends in business and in life.


  3. Hello James
    I believe there is a chap in US medicine, surgeon, who has become famous for advocating use of checklists. He says he has evidence that using checklists in surgery improves the safety of patients and success rate of operations. Why? Checklist forces people to do hat they know to do intellectually and yet they fail to do in practice.

    I wonder if the use of checklists would make difference in other domains? And I am sure that we live in a world where our ontological condition is to live at risk. Being an ontological condition there is nothing we can do about it. Planes will fall out of the sky occasionally, ships will sink, complex reactors will blow up from time to time. The unexpected is always there a little like viruses/disease: you get one handled and another one shows up nd you don’t see it until it strikes.


    • James Lawther says:

      Thanks for your comment Maz, I learn something new with every one. Ontology ~ the philosophical study of the nature of being, existence, or reality.

      I am a tragic believer in checklists, simply because I am less likely to forget things. And I do believe that one of our ontological conditions is forgetfulness

      Why would you make life hard for yourself?


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