Human Factors in Barrier Thinking

Industries with the potential for major accidents place great reliance on layers-of-defenses, or barrier thinking, to protect against incidents. Human performance continues to be the single most widely relied on barrier: whether as a defense in its own right, or in implementing, inspecting, maintaining and supporting engineered defenses. Human error, in its many forms, also continues to be a significant threat to the reliability of engineered and organizational defenses. While approaches to developing and assuring layers of defenses strategies have become increasingly formalized and rigorous in recent years, many organizations struggle to know how to ensure the human defenses they rely on are as robust as they reasonably can be when those strategies are developed and implemented. Using the operation of tank filling as an example, the presentation considers issues associated with the independence and effectiveness of human defenses.  The 2005 explosion and fire at the Buncefield fuel storage site is used as a case study to illustrate how human defenses can fail in the real world. Organizations can improve the strength of their human defenses by being clearer about exactly what it is they expect and intend of human performance to protect against threats. The presentation sets out challenges organizations can use to ensure the human defenses they rely on are as robust and reliable as they reasonably can be. And when incidents occur, examining how the barriers that were expected to be in place failed can make a powerful contribution to learning and improving the reliability of human performance.