... function. The probability of reliability and the probability of failure are opposite sides of the same coin. Therefore if P is the probability of failure and R is the probability of success ... elements fails then the whole control system fails. If the control system fails, then the system depends on the reliability of the pressure safety relief valve on the vessel. The safety of the manual ... becomes an audit and record of what was carried out or, if not carried out, then what was the alternative and why. The standard worksheet headings and what they mean, together with the guide words...