A few weeks ago, I led a workshop about risk in the wonderful city of Bergen on the west coast of Norway. On the toilet mirror, I noticed these stickers issued by the city council. The stickers pictured a hand on which a text was written with ‘permanent’ marker, saying “100% Clean Hand. 37 degrees”, and below the encouragement “Wash your hands!”.

Well-intended as this sticker surely is, here is a lot of nonsense going on.

Firstly, my mother wouldn’t agree at all. If I would have shown up at supper with permanent marker all over my hands she would definitely NOT have judged them as clean, not even 50%. I would have been sent to the bathroom to give them another good scrub, and no questioning that command.

Secondly, if I recall well, there are a lot of bacteria that thrive very well at 37 degrees Celsius. If you can believe Wikipedia, this is even the optimal growth temperature for e-coli, which is a bacteria that is commonly found in the lower intestine of warm-blooded organisms. Which is, well, the area that you probably have been in contact with on the toilet.

What we see here, are phenomena at work that we regularly encounter in safety (and health, quality, etc.). In this case, they are based on at least four Safety Myths:

  1. Believing that words don’t matter.
  2. Believing that firm language, based on absolutes, is good.
  3. Believing that perfection is good and can be achieved.
  4. Making information as simple as possible.

Let’s look at them one by one.

Myth 1: In this example words get a different meaning than we attach to them in everyday life. Clean doesn’t really mean clean, but okay, we might forgive that as a white lie because the permanent marker is just a gimmick to attract attention. But we most certainly don’t mean 100%; rather “clean enough to safely eat your lunch” or something similar. More about that below.

On a practical note, how would you know that the water is 37 degrees Celsius? This is the average body temperature, but your outer extremities are probably colder than that. So the water should feel warm, but how much more than your hands? So, do they actually mean 37 degrees, or something else?

Myth 2: Firm statements based on absolutes ooze a sense of certainty. Just check these:

100%. No Doubt. Definitely. Read My Lips. 

Wonderful, aren’t they? Many perceive this a better form of communication than more nuanced and somewhat ambiguous statements like “as clean as possible” or “good enough”. Often, however, this firm communication with use of absolutes lacks basis to do so. Cursory critical poking makes the arguments crumble. Washing your hands at 37 degrees Celcius will neither remove all dirt nor kill off all bacteria.

Interestingly, also the mentioned temperature is packed in a precise and firm statement, but the operational part (the temperature of the water you wash your hands with) will be approximate, at best. Unless we are required to bring thermometers to the bathroom.

Myth 3: Striving for perfection is unrealistic and actually counterproductive. Just imagine that you go for 100% clean hands. This would require either temperatures that will in fact hurt you, or a level of scrubbing that damages your skin (and leaves everything bloody, which isn’t really clean either). Additionally you will remove also the ‘good germs’ on your skin that you have need for.

Besides, you should not forget that some dirt may actually be good for you - it helps you build resistance (the process called hormensis).

Myth 4: Of course, information should be easy to understand, but simplification is often taken so far that it ends up in dumbing down a complex subject into a soundbyte. The result of the process of cleaning is a combination of temperature, the amount of water, time, chemicals (soap, alcohol) and mechanical techniques (e.g. what parts to pay special attention to and the amount of scrubbing). Feel free to experiment with those factors the next time you do the dishes, it may make the process much more fun too.

Stripping it down to just a temperature is severely misguided, as one may be led to believe that this is all that matters while it is not.

As my dad used to say: you shouldn’t believe everything you read. This sticker falls squarely into that category. Luckily these were stickers only intended for ‘common’ people and not occupations with higher risk of contamination and infection through contact, like health care (find better alternatives here and here). Still, it’s a questionable practice.


Safety Myth 101

You won’t find this exact example, but a great variety of these and other Safety Myths in the book Safety Myth 101 that has just been published through Mind The Risk. Available from a.o. Amazon - find links at:


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