Atomic Energy of Canada Limited

The Therac-25 radiation overdoses are often compressed into a cautionary story about two programming defects. The public record supports a harder conclusion. Timing-sensitive software paths were direct triggers in three well-understood accidents, but catastrophic exposure became possible because Atomic Energy of Canada Limited had moved essential protection from independent hardware into a software-controlled system whose hazard analysis, interface, testing, incident learning and corrective-action process were not adequate to the consequence of failure. Accountability therefore extends from code to architecture, from warnings to escalation, and from a repair being announced to evidence that it can stop harm even when another defect remains.