The most expensive number in engineering • Hacker News Board

Re: The most expensive number in engineering

#21

Post by gostsamo » Mon, May 31, 2021, 5:59 PM UTC

throwaway0a5e wrote: post #10

This analysis is great. It makes for a great blog post, university lecture or similiar. But unfortunately you can't have these kinds of discussions in an engineering meeting, or other shared context because anything that could be perceived as arguing for less safety will attract opposition because there's tons of people who want the cheap virtue points and ass-covering that goes with being the guy who's always in fav…

If you use such an argument in a real design meeting, you might be asked to leave. Either you have data to support changing the parameters of the assignment, or you keep your silence. Accusing everyone else in virtue signaling is at hominem attack that brings nothing to the table.

Re: The most expensive number in engineering

#22

Post by preinheimer » Mon, May 31, 2021, 6:00 PM UTC

supernova87a wrote: post #16

If you had the luxury of throwing away bridges or planes or space shuttles to test every possible circumstance, then I guess eventually the safety factor could conceivably come down to 1.0, right? You would've satisfied yourself that nothing in the real world was not in your simulations?

I don't think so.

- You'd also need to let them stand for 100 years or something to get a better view of all possible weather events. Oh wait, weather events are becoming more extreme. - Materials of production are imperfect. We're well past poorly made cast iron, but maybe something wasn't quite perfect when that bolt was cast. - Improper usage or external emergencies may still impact usage.

Re: The most expensive number in engineering

#23

Post by whatshisface » Mon, May 31, 2021, 6:02 PM UTC

wiml wrote: post #17

whatshisface wrote: post #15

Earlier quoted context omitted.

> It makes sure we calculate the loads correctly and use appropriate materials. No, it make sure that nobody dies when you calculate the loads incorrectly and use inappropriate materials.

Also helps when management decides to defer maintenance for a decade or two and someone drives a truck over it that's just a bit over the weight limit what could it hurt?

Perhaps implicit institutional knowledge of large safety factors is why management feels safe deferring maintenance.

Re: The most expensive number in engineering

#24

Post by santiagobasulto » Mon, May 31, 2021, 6:04 PM UTC

For context, the FS of elevator cables is ~10 (depending of the country).

EDIT: What's usually limiting in elevators (and that's why they say "max 4 people") are the breaks.

Re: The most expensive number in engineering

#25

Post by ajuc » Mon, May 31, 2021, 6:05 PM UTC

supernova87a wrote: post #16

If you had the luxury of throwing away bridges or planes or space shuttles to test every possible circumstance, then I guess eventually the safety factor could conceivably come down to 1.0, right? You would've satisfied yourself that nothing in the real world was not in your simulations?

> If you had the luxury of throwing away bridges or planes or space shuttles to test every possible circumstance, then I guess eventually the safety factor could conceivably come down to 1.0, right? You would've satisfied yourself that nothing in the real world was not in your simulations?

Isn't that the main advantage Space X has over NASA?

Re: The most expensive number in engineering

#26

Post by jollybean » Mon, May 31, 2021, 6:05 PM UTC

Not just 'stress safety' but all the other things.

A NASA project I was related to we logged every single bolt that went on the device, where it came from, the batch number, and had to keep all the old software around in the event we had to reconstruct something.

The amount of overhead was pretty amazing.

Most of that is for safety.

Re: The most expensive number in engineering

#27

Post by BurningFrog » Mon, May 31, 2021, 6:08 PM UTC

I'm sure engineers across geography and time all use a Factor of Safety.

I'm almost as sure that everyone keeps using the number people used before they joined the profession. Because if you decide to lower it, and a disaster happen, you are in very deep shit.

So once set, the number will tend to stick until forced to change by something extraordinary.

Which makes me very curious about how the number varies between independent domains. Do Japanese, Norwegian and US bridge builders all use the same number? Do builders of bridges, skyscrapers, and dams use similar numbers?

The answer would tell us something about how arbitrary these numbers are.

Re: The most expensive number in engineering

#28

Post by victor106 » Mon, May 31, 2021, 6:08 PM UTC

Reading this it seems like something like this could be used for software estimates as well?

Bake in a factor of safety into your estimates depending on the type of work, the track record of the team that’s doing the work etc

Re: The most expensive number in engineering

#29

Post by [deleted] » Mon, May 31, 2021, 6:09 PM UTC

santiagobasulto wrote: post #24

For context, the FS of elevator cables is ~10 (depending of the country). EDIT: What's usually limiting in elevators (and that's why they say "max 4 people") are the breaks.

[deleted]

Re: The most expensive number in engineering

#30

Post by zdragnar » Mon, May 31, 2021, 6:10 PM UTC

iscrewyou wrote: post #18

whatshisface wrote: post #15

Earlier quoted context omitted.

> It makes sure we calculate the loads correctly and use appropriate materials. No, it make sure that nobody dies when you calculate the loads incorrectly and use inappropriate materials.

Can’t tell if this is sarcasm. Because of goal of civil engineering is building man made objects with public safety in mind.

Another way to look at factor of safety is margin for error. Implementation variance, material variance, etc can all go wrong if something is designed to be exactly safe.

You need to know that something is redundantly safe, and which parts.