Safety system logic solver availability, loo2D and TMR

Four simplifications in the calculation of safety instrumented system logic solver performance measures (mean time to failure and risk reduction facto r) clarify the dependence on the various factors involved. These include fa ilure rate, fail safe fraction, diagnostics coverage and common cause. Appr oximate MTTF and RRF formulas are developed for 1oo2D and TMR logic solvers . These provide an explicit indication of which factors have the greatest i nfluence on improving safety. (C) 1998 Elsevier Science Ltd. All rights res erved.