• Medical Linear Accelerator
  • Mechanical restrictions were removed in favour of software control
    • Originally restricted operability from the Therac-20 and Therac-6
  • Programmed by one person
    • Minimal testing
    • Software designed without consideration of error handling
    • Software was not reviewed

1985 - Overdose of 100x the intended amount

  • Software Issue

    • Race condition
    • If the operator entered inputs too fast, the list of configurations will be malformed
    • Issue wasn't discovered earlier as it required the operator to be proficient
  • As a result of previous successful machines, the AECL believed in the safety.


  • Developers
  • AECL (Business)
  • Operator
  • FDA (Regulators)

How much is a human life worth?

  • This isn't the right question to ask
  • What's the purpose of the product - to save humans