Interim def stan 00–56: hazard analysis and safety classification of the computer and programmable electronic system elements of defence equipment

Interim Defence Standard 00–56 is an influential standard, particularly in its approach to the problem of design faults, and despite its title addresses, system safety as a whole. The paper contains an overview of the standard, concentrating on the way that accidents are categorised, and functions and components given safety integrity levels according to the safety implications of their operation or maloperation. The use of tabular schemes and claim limits for enforcing system architectures with good resistance to design faults and common mode failures is explained. The way in which the standard is ‘calibrated’ using numerical safety targets is also addressed. The paper concludes with a summary of the activities and supporting documentation required by the standard, and the plans for its further development.