The tomato test, or tomato slicing test, is a handy way to see if your knives could do with sharpening. The idea is that a properly sharpened blade should slice through the taut skin of a tomato with minimal pressure.

Somewhat counterintuitively, most cooks seem to agree that sharp knives reduce the risk of accidents as you don't have to push down as hard as with blunt knives.

To do the tomato slicing test: Place a tomato on a board and gently run the knife over the top surface. A sharp blade will glide through the tomato skin, cutting it precisely all the way down. You shouldn't need to apply any pressure if the knife has weight. If you need to push down to pierce the skin, it could be time to sharpen.

Cutting the top off the tomato first allows it to sit stably on its end, so you don't have to hold it.

Alternatively, you could use a serrated knife which is handy for foods with a hard outside and a soft inside.

The sharper the knife, the less mess you'll make and the easier you can ghost cook.

The tomato test

We all know that racing drivers overtake on the inside — it's the shorter, faster route. It was only relatively recently that I've found how useful it can be on a long drive too, not for racing, but for using the bend on a multilane road for easier, safer overtaking.

Perhaps this scenario will resonate: after cruising at a steady speed for miles of a long journey you slowly catch up with a car traveling just a few miles an hour slower. You're not driving fast enough to zip by them, but the difference is enough to slow your steady progress on a long journey, and if you're driving near the speed limit anyway you probably don't want to accelerate much to overtake.

On a multi-lane road like a motorway or freeway — not a single lane road where you'd be overtaking with reduced visibility on the corner in the opposing lane — timing your overtaking so you're on the inside of a bend and the slower car is on the outside allows you to get round the slower driver in a shorter time and without needing to travel nearly as fast.

And the converse is also true: if you've timed your overtaking when approaching a bend where you'll be on the outside you'll find that you'll have to go a lot faster to get round or perhaps that your intended overtaking is actually not getting you past at all.

Passing on an inside bend

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.

The Swiss Cheese Model

Forcing functions are a super way to help make things foolproof, or better, errorproof — as all of us make mistakes with designed things without being fools. You may have used your own forcing function when, in an attempt to make sure you remember your passport or tickets before a flight, you put them directly in front of the door so you couldn’t open it without noticing them. That little dialogue that asks you if you want to save your changes before closing your work, that’s a forcing function too.

My first memory of understanding a forcing function was when working with a giant machine capable of cutting through 100 pieces of paper at a time. The two buttons to operate it were on opposite sides of the machine. I couldn’t start the machine without spreading my arms out wide. There was then no way to also accidentally have your fingers in with the paper and near the blades when it started. Smart.

I learned this sense of forcing function from Don Norman’s classic The Design of Everyday Things. Also from Don, see Mapping.

The other sense of forcing functions for productivity is also really useful: helping kick ourselves into action.

Sketchplanations tagged with safety