You say that, but there will be a document somewhere telling people what the requirement is, and it will probably NOT say "Imagine the maximum possible amount of people that could physically fit, now add ten percent". And you might even find you need to track down the rationale in the engineering paperwork to know if the structural engineer envisioned this as a route crammed full of people or just a fun decorative element of the building that would technically be open to the public but rarely used. Not everything, build everywhere has to obey the same loading rules, many private homes have stairways that would be far too narrow, steep and poorly lit to be legal in commercial buildings for example.

When there was a balcony collapse in a foreign country I got interested and read the code where I live, the building regulations specify that a balcony or similar structure, which essentially hangs off the side of a building and so is unsupported at one side, must handle up to a certain load per square metre. Enough that a modest residential balcony can certainly hold two lovers, someone's spare bicycle and the decorative concrete flower beds they've put down to make it feel "outside". But what if instead of two lovers standing under the moonlight it's as many of the university rugby club as will physically fit? Ah, well then you're going to exceed the designed capacity and a code-compliant balcony might very well collapse.

All those tower blocks in England that are being retro-fitted because of the ones that burned down in London, their architects would have told you at the time they were definitely built to code, no extraordinary risk of fire. Then a bunch of people die in an out-of-control tower fire and - surprise - the politicians now claim the code meant you shouldn't ever have done that, and those towers were all built wrong but now they need to "clarify" the meaning. Sure.

I'm a software developer :-) What we usually call "software engineering" often doesn't take these kinds of issues into consideration. Even when I've worked with actual engineers (including P.Engs) the amount of "engineering" I've seen in my career as been vanishingly small. For example, I've worked in real time systems and we've had a performance budget. The number of times I've asked, "What did you do to ensure this will fit in the budget" and had people reply with something like "My code is fast. I don't think anyone can make it go faster" is ridiculous. Over time I've developed a kind of doubting attitude -- unless I see some evidence that you've done the due diligence, then I assume you've not.

Of course, what's common in my industry would obviously be fatal in other industries. I often tell my wife, "I don't have an unreasonable fear of heights. I have an unreasonable fear of engineers" :-) Still, I haven't died from having a bridge collapse under me yet, so I must be doing something right!

I know exactly what you mean. I used to work with someone who would constantly ask "where's the engineering? meaning where are the calculations, the data that support the conclusion that something would work? Refreshing words to my ears!