I'd love to know why a safety mechanism like this had an off switch, and under what circumstances that off switch is to be used. I feel like safety mechanisms should be always on, since they exist to prevent us from making mistakes when we forget things?
The one in Nesvizh:
https://www.iaea.org/publications/4712/the-radiological-acci...
The one in San Salvador:
https://www.iaea.org/publications/3718/the-radiological-acci...
The one in Soreq:
https://www.iaea.org/publications/3798/the-radiological-acci...
In each case the facility operator entered the irradiation chamber after switching off safety mechanisms (such as alarms or mechanisms placing the radiation source in a safe position, inside a pit) in order to unblock the conveyor system from packages that had become lodged in the mechanism. These facilities usually have a conveyor system that takes packages of products like food or medicine around a radiocative source to be sterilised. The packages seem to have a tendency to get stuck in the conveyor mechanism's parts often at which point proper procedure is to power everything down before someone can enter the facility to service the mechanism. Obviously that causes severe delays to production and obviously people simply override this procedure, that is in place to protect them. They go into the facility, they find the source in an active position and become irradiated.
My favourite of the bunch above is the one in Nesvizh, where the irradiation facility was built like a miniature maze from D&D, lacking only the guardian minotaurs with double axes (or Ogres, I guess). The radiation chamber was an actual maze, like a square spiral of concrete. The way to the source at the center of the maze was littered with pressure sensors that triggered alarms and there was even a moving hatch at the entrance that exposed a pit too deep and long to jump over. IAEA's investigation never found out how the operator managed to cross the pit, navigate the maze and get to the center of the chamber without triggering any alarms that would have normally stored the source to its safe position inside a dry pit, but he sure did it, then realised suddendly that the source was in the active position and ran back out. He died later of radiation poisoning before having the chance to tell anyone how he managed the feat.
It seems this procedure took too long so the operator only turned the key to "off" in the main control panel, then crossed the pit at the maze entrance on his own.
In my comment above I say they don't know exactly how he crossed this pit with the mechanical hatch, but I seem to have misremembered. The motor that moved the hatch was inside the pit and he could have stepped on it and jumped over to the far side. What the IAEA doesn't know is how he managed to cross a pressure plate after the pit that would have normally stored the source to its safe position.
What a crazy story, thanks for sharing it and the sources!
Edit: to expand on the pressure plate, maybe the logical fault was assuming the plate couldn't be accessed without the mantrap covered, requiring the key removed from panel.
Thanks for the pointer to the NTSB reports. I didn't realise they're all there!
Did you read the NTSB report on El Faro?
then you are in for a treat - just read how Chernobyl happened.
Especially when you hit something. Much, much faster.
If you were given N lightbulbs at the beginning of the year and all of them went "pop" or were "taken home", you won't have more until next year, no matter what. And by "you" here I mean support person, responsible for putting spare lightbulbs into sockets.
The scientist's performance assessment on the other hand is not tied to support supply chain troubles. He must continue with experiments and must use "hidden reserves" (disable safety system) if necessary.
There should be.