Risk significance and safety significance

Existing measures of the risk significance of elements of risk models (such as the Fussell-Vesely, or 'F-V', importance of basic events) are based on the properties of cut sets containing the element. A measure of safety significance (prevention worth, or PW-bar) is proposed, based on the properties of path sets containing the element. A high value of F-V means that cut sets containing the element contribute significantly to top event frequency; a high value of PW-bar means that path sets containing the element contribute significantly to top event prevention. The properties of PW-bar as a measure of basic event significance are illustrated first with a simple block diagram example, and then with an example based on nuclear power plant risk models. PW-bar can also be understood as a property of a set of success scenarios, and as such, can be applied more broadly than just as a measure of element significance