Incident investigation causal factors

The committee s analysis of the seven chemical events listed in Tables 2-1 and 2-2 showed that there were multiple causal factors for all of the selected events. (Note the committee could detennine causal factors only for incidents for which sufficient investigation data were available.) Rather than being specified for each incident, the causal factors identified by the committee are grouped into the following generic categories ... 

Post incident—through investigation of hazards-related incidents for causal factor determination... 

With regard to evaluating these factors, it is recommended that structured checklists be used, such as those provided by the HFAM method described in Chapter 2. These checklists provide an explicit link between the direct causal factors and management policies. Figure 2.12 shows how these checklists could be used to investigate possible procedures deficiencies, and the policies that led to the deficiencies, as part of the incident investigation. Similar checklists can be used to investigate possible culture problems (e.g., inappropriate trade-offs between safety and production) that could have been implicated in an accident. 

One approach is to mesh all investigation and root cause analysis activities under one management system for investigation. Such a system must address all four business drivers (1) process and personnel safety, (2) environmental responsibility, (3) quality, and (4) profitability. This approach works well since techniques used for data collection, causal factor analysis, and root cause analysis can be the same regardless of the type of incident. Many companies realize that root causes of a quality or reliability incident may become the root cause of a safety or process safety incident in the future and vice versa. 

Tool—A device or means used at a discrete stage of the incident investigation to facilitate understanding of event chronology, causal factors, and/or root causes. 

The team uses ready-made, off-the-shelf tree toois. The investigators do not have to buiid the tree, but rather apply the causal factors to each branch in turn, and discard those branches that are not relevant to the specific incident. 

The team reviews causal factors against investigative checkiists to determine why that factor existed at the time of the incident. A combined what if/pheckfist approach may be used. 

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. 

Checklist analysis tools can be a user-friendly means to assist investigation teams as they conduct root cause analysis.h) Each causal factor is reviewed against the checklist to determine why that factor existed at the time of the incident. The Systematic Cause Analysis Technique (SCAT)(9> is an example of a proprietary checklist tool. 

Eliminate other distractions from the room if possible. Do not allow the witness to see any documents, such as causal factor charts, fault trees, showing the incident investigation team analysis of the occurrence. This may he appropriate for later interviews when only specific information is needed or a specific time gap is being filled in. 

Johnson s interpretation of MES concepts is known as Events Causal Factor Charting (E CF), or Causal Factor Charting for short, and has been adopted as one of the building blocks of several methodologies for process safety incident investigation. 

These principles are not mandatory. The most important aspect is that the investigator understands the incident, and these principles are meant to facilitate that ohjective. Some investigators draw causal factor charts differently for example, some investigators do not distinguish between events and conditions. It is permissible to violate the above principles provided the method helps the investigator and others understand the incident. 

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... 

After the predefined tree has been used, a final generic cause test should be applied. The plant operating history, especially previous incidents, is considered to indicate if other generic management system problems exist. For example, repetitive failures may indicate generic causes that would not be apparent by only investigating the current incident. It is also an opportunity for a final overall review of the investigation to focus on the big picture, not just individual facts or causal factors. The team should ask, Are there any other causes that anyone has in mind that have not been included ... 

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. 

Some investigators review each of the causal factors to determine the immediate causes (unsafe acts or rmsafe conditions) of the incident, as an... 

The tool helps the investigator to understand and focus on the failed harriers, which are normally identified as causal factors. These failed harriers may need to he strengthened, replaced, or supplemented, especially where weak administrative controls are highlighted. Even successful barriers that prevented more serious consequences may require reinforcement. Therefore, barrier analysis can give the investigator valuable insights into how the incident happened and some of the multiple causes that need corrective action to prevent recurrence. 

Unlike the procedure followed in developing logic trees, the investigation team does not construct the tree. Rather they apply each causal factor to each branch of the predefined tree in turn, and those branches that are not relevant to the incident are discarded. This prescriptive approach offers consistency and repeatability by presenting different investigators with the same standard set of possible root causes for each incident. 

While the use of predefined trees does not directly challenge the investigation team to think laterally of other possible causes, many predefined trees present a wide range of causal factors, some of which the team may not have otherwise considered. It is therefore possible, but unlikely, that the incident could involve a novel root cause that was not previously experienced by those who developed the predefined tree. The addition of a final test based on another tool, such as brainstorming, can overcome this apparent weakness. 

Root (or primary) causes, immediate (or secondary) causes, and contributory factors are identified, analyzed, and discussed in this section of the report. As described in Chapter 9, process safety incidents are the result of many factors, and therefore singling out one cause is rarely the proper approach. Some experts indicate that if a fault tree or causal factor chart was developed as part of the investigation it should be incorporated to facilitate understanding. 

Each company s management style and safety systems have strengths and weaknesses. These strengths and weakness tend to influence the types and severity of incidents that might occur. An analysis of incident investigation findings in terms of causal factors, immediate causes, contributing causes,... 

Number of causal factors identified by incident investigation teams related to failures to properly apply or follow a safe work permit X ... 

To focus its analysis, the committee decided to examine events with the following characteristics (1) sufficient investigation had already been done to provide a basis for analysis and (2) the event could have had potentially serious outcomes, was complex in nature, was well documented, and provided a rich source of potential causal factors. With this as a rationale, the committee examined five dissimilar incidents in significant detail (Table 2-1). 

The committee s analysis was conducted on several levels. First, members investigated the causal factors for each of the seven events listed in Tables 2-1 and 2-2. They then developed a notional causal tree for each of the two events in Table 2-2 that were analyzed in depth. For illustrative purposes, a causal tree developed by the committee for the December 3-5,2000, incident at JACADS appears at Appendix F. The tree is a standard tool in reliability analysis and is particularly useful in human reliability analysis where operator actions contribute either positively or negatively to an incident. Lastly, the committee provides a series of general and specific observations about the events. 

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