ABSTRACT
The uses of computer control continue to grow and if we can learn from the incidents that have occurred we may be able to prevent repetitions. The failures are really human failures: failures to realize how people will respond; failures to allow for foreseeable faults. The equipment used is variously described as microprocessors, computers and programmable electronic systems. The last phrase is the most precise as microprocessors do not contain all the features of a general purpose digital computer. Leveson recommends that instead of trying to make software ultra-reliable, we should try to make the plant safe even if the software is unreliable. Adding alarms to a computerized control system is cheap and easy. The operators like to know when a measurement changes on a page that is not on display at the time so that they can intervene if necessary, so more and more alarms are added.
