Assume that the components are independent. At some point I wondered if there are any online services that allow you to make a simple calculation of reliability. For small numbers of common components, say M, EFcalc evaluates 2^M event/fault tree problems with every combination of the common components in either a failed (p=1.0) or not-failed (p=0.0) state. Using the patient's Urine, Sex, Age and GFR, the kidney failure risk equation provides the 2 and 5 year probability of treated kidney failure for a potential patient with CKD stage 3 to 5. To calculate, you need to know the availability factor. These common components destroy the independence of the gates above them, making the straightforward approach unusable. Perhaps the first and most fundamental measure of (un)reliability is the failure rate of a component or system of … where P(A) is the failure probability of the alarm system and P(S) is the failure probability of the emergency shutdown system. The failure rate of a system usually depends on time, with the rate varying over the life cycle of the system. Z