In the Therac-25
accidents a radiotherapy machine with software controller
had a hardware interlock removed, but the software had no
interlock software and failed to maintain essential
invariants:either electron beam mode or stronger beam and
plate intervening,to generate X-ray. Several deaths resulted
due to burning. The programmer had no experience with
concurrent programming.
The International Atomic Energy Agency declared
radiological emergency in Panama on 22 May,2001. 28 patients
overexposed;8 died,of which 3 as result; 3/4 of surviving 20
expected to develop serious complications which in some cases
may ultimately prove fatal. Experts found radiotherapy
equipment working properly;cause of emergency lay with data
entry If data entered for several shielding blocks in one
batch then an incorrect dose was computed. The FDA concluded that interpretation of beam block
data by software was a factor.
Ariane-5 (June 1996). The European Space Agency complete
loss of unmanned rocket shortly after takeoff due to exception
thrown in Ada code faulty code which was not even needed after
takeoff due to change in physical environment. Undocumented
assumptions were violated.