Incident Investigation timeline

This chapter addresses methods and tools used successfully to identify multiple root causes. Process safety incidents are usually the result of more than one root cause. This chapter provides a structured approach for determining root causes. It details some powerful, widely used tools and techniques available to incident investigation teams including timelines, logic trees, predefined trees, checklists, and fact/hypothesis. Examples are included to demonstrate how they apply to the types of incidents readers are likely to encounter. 

Like a simpler timeline, a sequence diagram does not identify root causes, and therefore it should be used as part of a combined methodology with other tools. In this respect, a sequence diagram may be used in place of the timeline within the two main incident investigation methodologies presented in this chapter. 

Setting the above knowledge and proposals together leads to integrated incident investigation procedure which is stUl based on the timeline development, causal factor identification and causal factor chart development, but which allows the determination of different Incident Cause Level for each of multiple causes. If the Incident Cause Level of specific cause is outside the internal safety management, the apph-cation of non-hnear analysis method is recommended. 

The incident investigation showed that the algorithm in the FPCP software had a serious limitation, which meant that in a very specific situation multiple spikes on the AOA signal from only one of the ADlRUs could generate a nose-down elevator command. A timeline for the event is shown in Fig. 5.3. 

Development of the timeline should start as soon as facts emerge about the incident. By starting early, the investigator will become aware of... 

Once the evidence has heen collected and a timeline or sequence diagram developed, the next phase of the investigation involves identifying the causal factors. These causal factors are the negative occurrences and actions that made a major contrihution to the incident. Causal factors involve human errors and equipment failures that led to the incident, hut can also he undesirable conditions, failed harriers (layers of protection, such as process controls or operating procedures), and energy flows. Causal factors point to the key areas that need to he examined to determine what caused that factor to exist. 

Analysis, that can assist with the identihcation of causal factors. The concepts of incident causation encompassed in these tools are fundamental to the majority of investigation methodologies. (See Chapter 3 for information about the Domino Theory, System Theory, and HBT Theory.) The simplest approach involves reviewing each unplanned, unintended, or adverse item (negative event or undesirable condition) on the timeline and asking, Would the incident have been prevented or mitigated if the item had not existed If the answer is yes, then the item is a causal factor. Generally, process safety incidents involve multiple causal factors. 

Causal factor identification tools are relatively easy to learn and easy to apply to simple incidents. For more complex incidents with complicated timelines, one or more causal factors can be overlooked, ultimately leading to missed root causes. Another disadvantage is that an inexperienced investigator could potentially assume that suppositions are causal factors, when in reality the supposed event or condition did not occur. 

A diagram depicting the sequence of events leading to an incident has a number of advantages over a simple timeline that may be summarized in three main areas investigation, identifying actions, and reporting as shown below.h)... 

Once the timeline or sequence diagram based upon the actual scenario has been developed, the next phase of the investigation involves identifying the causal factors. Causal factors involve human errors and equipment failures that led to the incident, but can also be undesirable conditions and... 

Once the evidence has heen collected, a timeline or sequence diagram developed, and the actual scenario confirmed, the investigation can proceed to the next stage, the identification of causal factors. These causal factors are the negative events and actions that made a major contrihution to the incident. 

Establish a timeline. The investigation of almost every significant incident will require the development of a time line to depict the sequence of events before, during, and after the incident. 

Once the facts of the incident have been established as shown in the previous chapter, the next step in the investigation is to develop a timeline or story line (Figure 11.7). A feedback loop from... 

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