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Comment by steckerbrett | Hacker News Reader

I think the most important button ever created is the SCRAM (emergency shutdown) button on a nuclear reactor, they don't fuck around making it look pretty. You know where the button is and you never ever want a seconds hesitation in getting it pushed.

https://c2.staticflickr.com/8/7244/7300035260_8e872e201c_b.j...

Probably somewhere close on the list is the MAGNET STOP button on a MRI machine, it destroys the superconducting magnet and vents the incredibly expensive helium into the atmosphere.

http://a406.idata.over-blog.com/0/01/25/36/magnetic-field-st...

No cover, no toggle, no delay, you want them big and red and able to be pressed by someone with two broken wrists.

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Quenching the magnet has a chance to cause damage, but it doesn't necessarily destroy the magnet.

And while liquid helium isn't cheap, filling the dewar once isn't that expensive compared to the MRI itself. You have to contiuously refill liquid helium, which is a significant running cost.

I meant it destroys the superconducting-ness rather than the whole magnet. The costs of not having a MRI machine are probably even higher than operating one, though I'm not sure how you'd go about quantifying that.

I remember working with a chap who had what he described as "the worst support call ever" - involving an irate engineer who was apparently standing on top of a nuclear reactor and complaining that the monitoring system had crashed.

He said it wasn't particularly fair as the company he worked for wasn't responsible for the system having the problem, they just did the display part and made the mistake of displaying their company name rather conspicuously. Try explaining that to an angry man standing on top of a nuclear reactor...

How does an "emergency" shutdown button get that dirty? That looks heavily used.

Other photos of SCRAM buttons show signs of wear too, from my limited knowledge I think a SCRAM is also used in normal operating procedure as a rather extreme "off" button.

https://en.wikipedia.org/wiki/Scram#/media/File:NS_Savannah_...

The SCRAM button in that photo is from the EBR-1 breeder reactor in Idaho.

It got pushed once in 1955 by a supervisor who had to jump over the table to hit it, because the employee in charge of the panel was chatting on the phone with his wife.

It was hit too late though, and half the core melted down.

(That's particularly bad for breeder reactors, because it can cause a nuclear explosion.)

Ironically, the entire chain-of-events was precipitated by a different wrong button being pressed.

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