No, I’m not a anti-technology hippie with tie-dye pants and hairy underarms, I’ve just read (again!) the incredible story of how at least 6 people were zapped with high-powered radiation beams, and how three of them died as a result. Now if that’s not a decent system failure, ‘slap ma face with the side of a hawg’, or so says my uncle who likes to think he’s Canadian.
The story I’m referring to is that of the Therac-25, a radiation machine with two modes: electron-beam therapy (low doses of electrons over a short period of time) and megavolt X-ray therapy (using the full power of the machine by delivering X-rays produced by high-energy electrons in a powerful beam. A metal plate spreads the beam out before contact with the patient, and lowers the intensity).
The weak links were the software in the machine and the user interface. The code was sloppy and some of it was reused from a previous machine which had hardware components to cover faults in the software, whereas the Therac-25 was more software-based. Furthermore, when a particular set of commands was entered too quickly, the machine malfunctioned and it resulted in activating the high-powered and dangerous X-ray mode, but without the metal plate in place. There was nothing to tell the operator that anything was wrong… except for the patients screaming, jumping off the table and complaining of electric shocks. But according to the display, they had only recieved one-tenth of the dose.
They clued on when the patients started dying of massive radiation poisoning. The first victim was Ray Cox, who had several blasts of more than 125 times the prescribed dose.
So that’s the backstory, let’s apply it to the WorkSafeBC ‘People, Workplaces and Management’ model. Sounds boring, but it’s a good way to show all the different elements of a system that came together to make an accident.
You can see how this model gets very crowded in a complex accident.
There you have it! You can see how all those elements, when combined, make a deadly accident.
And for a final note: Ray is such an ironic name to have in this incident.
daniellewolhuter 
Leave a comment