Safety assessment for safety-critical systems including physical faults and design faults

Two types of faults, design faults and physical faults, are discussed in this paper. Since they are two mutually exclusive and complete fault types on the fault space, the safety assessment of safety-critical computer systems in this paper considers the hazard contribution from both types. A three-state Markov model is introduced to model safety-critical systems. Steady state safety and mean time to unsafe failure (MTTUF) are the two most important metrics for safety assessment. Two homogenous Markov models are derived from the three-state Markov model to estimate the steady state safety and the MTTUF. The estimation results are generalized given the fault space is divided by M mutually exclusive and complete types of faults