Causal Factors Chart

Causal Factors Identification of Factors Possible Corrective Actions 

Environmental unsafe Hazardous processes management failed to Job hazard analysis or formulation of safe 

Defective, overused Buildings, machines, or equipment worn, cracked, broken, or defective Inspection replacement proper maintenance 

Improperly guarded Work areas, machines, or equipment that are unguarded or inadequately guarded Inspection check plans, blueprints, purchase orders, contracts, and materials provide guards for existing hazards 

Unsafe dress or apparel Management failed to provide/specify the use of goggles, respirators, safety shoes, hard hats, or safe apparel Provide proper apparel or personal protective equipment specify acceptable dress, apparel, or protective equipment 

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In the second case study, variation tree analysis and the events and causal factors chart/root cause analysis method are applied to an incident in a resin plant. This case study illustrates the application of retrospective analysis methods to identify the imderlying causes of an incident and to prescribe remedial actions. This approach is one of the recommended strategies in the overall error management framework described in Chapter 8. 

The events and causal factors chart for this incident is shown in Figure 7.9. The primary sequence of events is shown horizontally in bold boxes. Secondary events are shown in the other boxes, and conditions are in ovals. From the diagram three causal factors were identified and carried forward to the Root Cause Coding to establish the root causes of the causal factors. 

Buys, R. J., and Clark, J. L. Events and Causal Factors Charting. Revision 1, Idaho Falls, ID System Safety Development Center, Idaho National Engineering Laboratory, 1978. (DOE 76-45/14 SSDC-14)... 

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. 

This step is always performed. Using analysis tools and methods such as fault trees, causal factor charting, checklists, predeveloped trees, or alternative methodologies will help to identify the root causes of the failures. 

Sequence diagrams are a more elaborate graphical depiction of a timeline, and allow the investigator to present related events and conditions in parallel branches. These sequence diagrams are also known as causal factor charts. 

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. 

The technique for developing causal factor charts share a number of fundamental principles with MES and STEP. Basic principles for constructing sequence diagrams ) are given below. 

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. 

The first step in developing a causal factor chart is to define the end of the incident sequence. Construction of the chart should start early from the end point and work backward to reconstruct what happened before the incident by identifying the most immediate contributing events. 

Starting at the end point, it is then necessary to convert the collected evidence into statements of either fact or supposition. By taking a small step backward in time, the investigator asks, what happened just before this event. It is important to clearly distinguish any assumptions as supposition. Then the investigator writes a statement for what happened, and enters the fact (or supposition) as an event block or condition oval on the causal factor chart at the appropriate location on the timeline. Statements that caused an event to occur should be treated like conditions and added in an oval. 

The entire causal factor chart is then reviewed to identify any omissions or gaps in the chronology. Additional effort is required to gather further evidence to close these gaps. If new data are inserted into the timeline, the sequence should be retested for sufficiency. Some gaps may remain even after this additional effort. The causal factor chart review should also identify and eliminate any facts that are not necessary to describe the incident. Detailed rules for causal factor charting are shown in Figure 9-7. 

If any of these facts are relevant, convert them into building block format and insert them into the Causal Factor Chart at the appropriate location on the time line. If any facts are inserted between Fact B and A, then retest each pair of facts for sufficiency as stated in steps 7 and 8, and repeat steps 9 and 10 as necessary. 

Review the entire Causal Factor Chart and eliminate any facts that are not necessary to describe the incident. 

Find the facts in the main sequence on the Causal Factor Chart that describe a component failure or a human error. Ensure the fact is not describing a management system failure (i.e., ensure the fact is not a root cause, near root cause, or root cause category). The identified negative events/conditions are candidate causal factors. Any candidate causal factor that is not dependent on another candidate causal factor is a valid causal factor. 

An example of a causal factor chart for a relatively simple incident is shown in Figure 9-8. In this example, there are two redundant pumps, one of which is required to supply feed to a reactor downstream. The operator is requested to change-over operation from Pump A, which is running, to Pump B, which was previously shutdown. Instead of opening Pump B suction valve, the operator opens the wrong valve, causing the Reactor to trip on low flow detection. 

The next phase of investigation involves developing a preliminary chronological description of the sequence of events that led to the failure. Timelines can be developed in various formats and levels of detail, from simple lists of events to complex sequence diagrams or causal factor charts, usually dependent upon the particular circumstances of the investigation being conducted. 

First, it is necessary to identify the multiple causal factors of the incident. The procedures in Causal Factor Identification may be used to identify tbe causal factors from a timeline or sequence diagram (including a causal factor chart). 

After the interviews and other evidence gathering activities are complete, a more detailed causal factor chart can he developed. Causal factors are indicated hy hlack triangles. 

Four causal factors are identified. (Note that each causal factor includes all of the information attached to it in the causal factor chart.)... 

A more complex incident may require the use of harrier analysis or change analysis to assist in developing the causal factor chart. 

FIGURE 9-31. Complete causal factor chart for fish kill incident (continued on next page). 

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. 

Fig. 1 shows the example of a causal factor chart developed for a single causal factor (rectangle denoted by (14)). A few chains of underlying causes resulted from constant asking WHY. 

Figure 1. Example of a part of causal factor chart.

Root cause identification connects the specific chains of underlying causes from causal factor chart to generic chains of underlying causes from the Root Cause Map. Final nodes of the generic chains represent the most accurate causes in the safety management system. 

Suppose that a causal factor chart is developed (see example in Fig. 1). However, there is no warranty, that each of the specific chains of underlying causes from the causal factor chart wiU be coimected to a corresponding generic chain of underlying causes from the predefined tree. Some of causal factors may have no root causes. 

The construction of a causal factor chart usually starts on the first causal level and proceeds to lower ones. A formalized start inside the process multicomponents may be required in order to assure that no exception from this natural procedure will occur. 

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