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Isn't every accident preventable in hindsight since you know exactly what the failure mode was? If they'd built the generators on a hillside that was washed aw

Isn't every accident preventable in hindsight since you know exactly what the failure mode was? If they'd built the generators on a hillside that was washed away in a mudslide the article would read "Critical backup generators were built on unstable hillside despite warnings from scientists".

joe_the_user 11y ago
Indeed, and most accidents can shown to have been preventable "if international best practices and standards had been followed, if there had been international reviews, and had common sense prevailed in the interpretation of pre-existing geological and hydrodynamic findings." [the article] But claims would seem to be little more than a thin gloss on the unbreakable unobtainium[1] of your hindsight. [1]https://en.wikipedia.org/wiki/Unobtainium https://en.wikipedia.org/wiki/Unobtainium
WalterBright 11y ago
The idea with building safe systems is not to imagine what could cause subsystem X to fail, but to figure out how to cope when subsystem X fails. The most obvious design failure at Fukushima was not "how big a tsunami we should protect against" but not asking "how will we cope when the seawall fails". If the critical backup generators had been in a bunker designed to protect them from a seawall breach, the disaster would not have happened.
- lucozade 11y ago
  Although it's been a very long time since I did engineering that could actually kill people, this idea that you focus on what can go wrong and how you mitigate it has stuck with me and has proved useful in lots of things. Having said that, the next questions are usually: what is the likelihood of it going wrong and what is the cost of mitigation? I don't envy the people making those decisions on something like a nuclear reactor, with or without hindsight.
  - WalterBright 11y ago
    At some point, you do assign a probability of systemic failure threshold, as nothing is perfect. The idea behind orthogonal backups, however, is that since they are independent, very high reliability can be achieved with low reliable components. For example, if you've got a main with 90% reliability, and a backup with 90% reliability, the combined reliability is 99%. This can be a lot easier and less expensive to achieve than making one component 99%. The backup generators could have a cheap extra seawall built around them, or could have simply raised them up on a 10 foot platform, or built them with snorkels like a jeep designed to cross streams. Building a heftier main seawall would have been an order of magnitude or two more expensive.
- walshemj 11y ago
  Or have plans to have backup power airlifted into place.

joe_the_user 11y ago

Indeed, and most accidents can shown to have been preventable "if international best practices and standards had been followed, if there had been international reviews, and had common sense prevailed in the interpretation of pre-existing geological and hydrodynamic findings." [the article] But claims would seem to be little more than a thin gloss on the unbreakable unobtainium[1] of your hindsight. [1]https://en.wikipedia.org/wiki/Unobtainium https://en.wikipedia.org/wiki/Unobtainium

WalterBright 11y ago

The idea with building safe systems is not to imagine what could cause subsystem X to fail, but to figure out how to cope when subsystem X fails. The most obvious design failure at Fukushima was not "how big a tsunami we should protect against" but not asking "how will we cope when the seawall fails". If the critical backup generators had been in a bunker designed to protect them from a seawall breach, the disaster would not have happened.

lucozade 11y ago
Although it's been a very long time since I did engineering that could actually kill people, this idea that you focus on what can go wrong and how you mitigate it has stuck with me and has proved useful in lots of things. Having said that, the next questions are usually: what is the likelihood of it going wrong and what is the cost of mitigation? I don't envy the people making those decisions on something like a nuclear reactor, with or without hindsight.
- WalterBright 11y ago
  At some point, you do assign a probability of systemic failure threshold, as nothing is perfect. The idea behind orthogonal backups, however, is that since they are independent, very high reliability can be achieved with low reliable components. For example, if you've got a main with 90% reliability, and a backup with 90% reliability, the combined reliability is 99%. This can be a lot easier and less expensive to achieve than making one component 99%. The backup generators could have a cheap extra seawall built around them, or could have simply raised them up on a 10 foot platform, or built them with snorkels like a jeep designed to cross streams. Building a heftier main seawall would have been an order of magnitude or two more expensive.
walshemj 11y ago
Or have plans to have backup power airlifted into place.