TIMEOUT FOR TECH Figure 1. A person trying to lift an object is a familiar example of a system at risk of failing. (Courtesy of Gary T. Fry.)
UNDERSTANDING FAILURE RISK What methods can be used to quantify it?
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BY GARY T. FRY, PH.D., P.E., VICE PRESIDENT, FRY TECHNICAL SERVICES, INC.
elcome to “Timeout for Tech with Gary T. Fry, Ph.D., P.E.” Each month, we examine a technology topic that professionals in the railway industry have asked to learn more about. This month, we discuss risk of failure and methods we can use to quantify this risk. Even after expending our best efforts, in most human endeavors, there is no such thing as “zero probability of failure.” 40 Railway Age // May 2022
Engineered systems are not exceptions to the rule. Consequently, assessing risk of failure is an essential part of planning, designing, building, operating and maintaining these systems. In particular, the concepts of capacity and demand and their relative magnitudes are the most important objectives to control, especially in the context of ensuring safety. We begin with a familiar example that illustrates the essential features of a typical risk of failure assessment problem.
Figure 1 (above) is a photograph of a person trying to lift a pumpkin. What is the risk that this effort will fail? To answer the question, we need to know this person’s maximal lifting capacity and the weight of the pumpkin. If the weight of the pumpkin exceeds the person’s maximal lifting capacity, we might reasonably conclude that there is a risk of failure approaching 100%. Conversely, if the person’s maximal lifting capacity exceeds the weight of the pumpkin, we assess a risk of failure close to 0%. railwayage.com