4 ms·

I'll be sure to keep your wisdom in mind next time I have to reset the way too conservatively sized circuit breaker integral to the contractor that runs in my f

I'll be sure to keep your wisdom in mind next time I have to reset the way too conservatively sized circuit breaker integral to the contractor that runs in my fume extractors. Damn near anything can kill you. Context matters. In most cases a consumer lawnmower should probably have a deadman switch. Plenty of people have been hurt or killed over the years by poorly thought out fail "safes". It's easy to make low effort online comments about safety but when someone comes along and re-uses your widget in a use case you don't expect your assumptions may not hold. You rarely have the context to determine what's safe unless you know the end situation in which the equipment will actually operate. For a lawnmower you do. When you start generalizing your control system and applying it to other stuff you don't. Absolutist rules of thumb are worth what you pay for them.

rascul 4y ago
> In most cases a consumer lawnmower should probably have a deadman switch. It's under the seat. With nobody in the seat, that had to be modified for this mower.
- swayvil 4y ago
  They've got them on push mowers too. You gotta keep a handle gripped for the mower to run. Let go and it stops
  - hinkley 4y ago
    One of the complications of this is that it's very hard to hold the switch on certain types of terrain. Objectively, well over 80% of that terrain is situations where you have no business running a lawnmower in the first place, and so 'good!' is mostly the correct response to such complaints. But it's still a pain in the ass in other situations, like cornering past bushes. Me, I just don't have grass anymore. Fuck grass. It's a bunch of bougie bullshit from a line of the French Aristocracy who ultimately wound up with their heads in baskets. Maybe we shouldn't be copying them.
    - causi 4y ago
      One of the complications of this is that it's very hard to hold the switch on certain types of terrain I've never used a mower fitting that description. On all of mine the safety handle runs the entire length of the push handle and you have to essentially let go of the mower to disengage it.
kayodelycaon 4y ago
This is really pedantic. The rule is any system that risks serious harm to a person in the course of normal operation should be fail-safe, not fail-dangerous. Examples include stuff with blades, hammers, or swinging arms moving at high speed or with great force.
- Maxion 4y ago
  Yep there's a reason why all lawn mowers have a dead-man switch.
  - tuatoru 4y ago
    *should have
- logifail 4y ago
  > The rule is any system that risks serious harm to a person in the course of normal operation should be fail-safe, not fail-dangerous. I used to work in a Chemistry lab, one in which one of my lab-mates once had a explosion while he heated something which wasn't what he thought it was. I was the guy who phoned for the ambulance (and got the fire service included for free, but maybe that makes sense if you work in a lab). I went to the front entrance to meet the firefighters as instructed, after identifying myself they asked me "do you have anything dangerous in your lab?" I was probably still high on the adrenaline (there had been a fairly loud bang and the glass side windows of my colleague's fume hood were blown out) but I recall being unable to answer that question. I think I eventually said "Yes, of course we have dangerous stuff, you have anything particular in mind?" Context really does matter!
Syonyk 4y ago
> * I'll be sure to keep your wisdom in mind next time I have to reset the way too conservatively sized circuit breaker integral to the contractor that runs in my fume extractors.* You might enjoy the NEC section on fire pump systems. It's a complete flip from the rest of NEC, requiring design around "Keep the fire pumps running at all costs, even if you're in the process of melting down the windings." Separate wiring conduits, handling full locked rotor current indefinitely, etc. The logic, reasonably enough, is that if the fire pumps are running, you probably have way, way bigger problems that will be made worse if your fire pump system trips off to protect the wiring.
- ad404b8a372f2b9 4y ago
  On that topic, the Cathode Ray Dude posted a really interesting video yesterday talking about battle-shorts, a mechanism used to circumvent power relay fail-safes in military equipment. There were some interesting comments about other cases like the fire pump systems you mentions. https://www.youtube.com/watch?v=wpJ_6LCly4A https://www.youtube.com/watch?v=wpJ_6LCly4A
causi 4y ago
What is this screed even trying to say? "Someone might reuse your failsafe in a way that actually makes it dangerous"? Then it's not a failsafe anymore and the second designer is an idiot. Like with the firehose example, it isn't the pumping that will kill you it's the not-pumping, therefore your failure state should halt the not-pumping.

rascul 4y ago

> In most cases a consumer lawnmower should probably have a deadman switch. It's under the seat. With nobody in the seat, that had to be modified for this mower.

swayvil 4y ago
They've got them on push mowers too. You gotta keep a handle gripped for the mower to run. Let go and it stops
- hinkley 4y ago
  One of the complications of this is that it's very hard to hold the switch on certain types of terrain. Objectively, well over 80% of that terrain is situations where you have no business running a lawnmower in the first place, and so 'good!' is mostly the correct response to such complaints. But it's still a pain in the ass in other situations, like cornering past bushes. Me, I just don't have grass anymore. Fuck grass. It's a bunch of bougie bullshit from a line of the French Aristocracy who ultimately wound up with their heads in baskets. Maybe we shouldn't be copying them.
  - causi 4y ago
    One of the complications of this is that it's very hard to hold the switch on certain types of terrain I've never used a mower fitting that description. On all of mine the safety handle runs the entire length of the push handle and you have to essentially let go of the mower to disengage it.

kayodelycaon 4y ago

This is really pedantic. The rule is any system that risks serious harm to a person in the course of normal operation should be fail-safe, not fail-dangerous. Examples include stuff with blades, hammers, or swinging arms moving at high speed or with great force.

Maxion 4y ago
Yep there's a reason why all lawn mowers have a dead-man switch.
- tuatoru 4y ago
  *should have
logifail 4y ago
> The rule is any system that risks serious harm to a person in the course of normal operation should be fail-safe, not fail-dangerous. I used to work in a Chemistry lab, one in which one of my lab-mates once had a explosion while he heated something which wasn't what he thought it was. I was the guy who phoned for the ambulance (and got the fire service included for free, but maybe that makes sense if you work in a lab). I went to the front entrance to meet the firefighters as instructed, after identifying myself they asked me "do you have anything dangerous in your lab?" I was probably still high on the adrenaline (there had been a fairly loud bang and the glass side windows of my colleague's fume hood were blown out) but I recall being unable to answer that question. I think I eventually said "Yes, of course we have dangerous stuff, you have anything particular in mind?" Context really does matter!

Syonyk 4y ago

> * I'll be sure to keep your wisdom in mind next time I have to reset the way too conservatively sized circuit breaker integral to the contractor that runs in my fume extractors.* You might enjoy the NEC section on fire pump systems. It's a complete flip from the rest of NEC, requiring design around "Keep the fire pumps running at all costs, even if you're in the process of melting down the windings." Separate wiring conduits, handling full locked rotor current indefinitely, etc. The logic, reasonably enough, is that if the fire pumps are running, you probably have way, way bigger problems that will be made worse if your fire pump system trips off to protect the wiring.

ad404b8a372f2b9 4y ago
On that topic, the Cathode Ray Dude posted a really interesting video yesterday talking about battle-shorts, a mechanism used to circumvent power relay fail-safes in military equipment. There were some interesting comments about other cases like the fire pump systems you mentions. https://www.youtube.com/watch?v=wpJ_6LCly4A https://www.youtube.com/watch?v=wpJ_6LCly4A

causi 4y ago

What is this screed even trying to say? "Someone might reuse your failsafe in a way that actually makes it dangerous"? Then it's not a failsafe anymore and the second designer is an idiot. Like with the firehose example, it isn't the pumping that will kill you it's the not-pumping, therefore your failure state should halt the not-pumping.