Accident investigation processes applied today focus primarily on management system root causes. However, current Safety Management Systems have not proven as effective at improving major accident performance - high consequence low frequency events, as they have for occupational accidents. A new method, titled BSCAT, is described which extends traditional root cause investigation methods to an accident pathway built on barrier based risk assessment diagrams (bow ties). This method is shown to be more straightforward to apply than traditional root cause methods, but allows greater useful information to be extracted from an investigation. Every incident involves some barriers failing. The method is designed to be applied routinely to all incidents on a facility by safety or supervisor grade staff. The combination of modern Safety Management Systems with Risk Assessment, underpinned by incident feedback for both, is believed capable of enhancing process safety results, which SMS on its own has not achieved. A case study shows how this might be applied in a real facility.

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Accident investigation has been thought of as a well developed process. It is mandated in offshore safety management system standards including API RP 75 (2004) and the new US BOEMRE SEMS (2010) regulation. It is an integral element of the onshore OSHA 1910 Process safety Management regulation and the international safety standard OHSAS 18001. It underpins the lessons learned aspect of safety management so that management and staff can understand the causation of prior incidents and act to prevent their recurrence.

Today most incident investigations methods drive towards what is termed "root causes", although the meaning of this varies according to the context. In many mechanical failure incidents the root cause will be a technical fault - wrong material, excessive vibration, etc. However, most investigators regard root cause as the underlying safety management system deficiency that allowed the incident to occur. The specific cause is usually termed the direct or immediate cause. A root cause is a fundamental, underlying, system-related reason why an incident occurred that identifies correctable failures in the management systems. There is typically more than one root cause for every process safety incident.

Current regulations regarding incident investigation tend to be non-prescriptive as to approach. For example, the API RP 75 (2004) standard requires that management must establish a system to investigate all incidents with the potential for serious safety or environmental consequences. The investigation should be carried out by a competent person and address needed corrective actions. These should be followed-up in a timely manner.

A problem with the focus on systems failure is that it tends to focus too much on the safety management system and not enough on the risk controls that have degraded or failed and allowed the incident to occur. This paper describes an investigation approach that combines a management system root cause technique with barrier based risk assessment, the bow tie method, allowing identification of deficiencies to both, and direct improvement actions to the management system and to the risk assessment.

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