Comparison of economic impacts of safe and dangerous failure of safety system

People operate many of relatively dangerous equipment such as cars, trains, petrochemical refineries or nuclear power plants. Why human society accepts their processing? The main reason is the benefit that these machineries bring. Their dangerousness is wrongly understood by the general public only as a consequence of a dangerous event, but we know from the theory of dependability and risk controlling that risk is calculated as a combination of more factors, at least of consequences and the expected number of occurrences of unwanted events. This mentioned unwanted event could be a commonly understood failure but also e. g. the false action of a safety system when its impact is not needed (so-called safe failure). The consequence of the false impact is economic loss resulting from process stoppage. The consequence of dangerous failure is mostly expressed by number of lost human lives. However human life can be transferred into financial expression too. People developed more and more reliable machinery to avoid losses of lives. One principle of increasing dependability is to back up the potentially dangerous machinery. This is mostly done by two parallel lines, but there are more options of backuping. This paper deals with three options of back-up algorithms - averaging of three independent signals, voting algorithm 2003 and voting algorithm 2003 with the ability of validation of each signal line. The ratio between safe and dangerous failures depends on the type of back-up. This article deals with the economic evaluation of false impact, dangerous event and the ratio between those two types of faults in dependence on the type of back-up.