Some statistical characteristics of a repairable, standby, human & machinesystem

This paper presents a model for a 2-unit s-identical system with one operat ing-unit (OU) online and the other, warm standby-unit (SU) human machine sy stem. The failure rates for both the OU & SU (common-cause, human error, an d hardware failures) are constant, whereas the repair times are arbitrarily distributed for a failed system. Linear ordinary differential equations ar e used to obtain a general expression for system steady-state availability for failed system by taking the repair time distributions as Gamma. General ized expressions for system reliability, and time-dependent availability ar e presented. Graphs demonstrate the impact of human error on system steady- state availability for various distributions, and some physical meaning is given. As time increases, the time-dependent availability decreases for exp onential repair time distribution for different values of initial human err or rate.