Tier Diagramming

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Tier Diagramming

In accident investigations, root cause analysis is very important activity. Tier diagramming is one of the best approaches that can be used to perform root cause analysis. Tier diagramming singles out the root causes of an accident and the management level that is charged with the responsibility of correcting the accident causal factors. Tier diagram are frequently used by the investigators to hierarchically classify causal factors resulting from event and causal factor analysis (Sklet, 2002). Linkages among the causal factors are the developed and facilitate establishment of the possible root cause (U.S. Department of Energy, 1999). Diagrams may be developed for each level responsible for the actions with accident.

The first step in application of a Tier-diagramming on the painting booth accident root cause analysis is to create an effect cause analysis chart to give guidance on the main causal factors (Sklet, 2002). In this case the main causal factors noted from the chart are the: company’s exclusion of painting booth from preventive maintenance practices, snapping of the fan belt, the fan stops to work, organic vapor are not removed in the paint booth; manometer failure; in ability to detect airflow in the booth; accumulation of organic vapor in the booth; supervisor failure to wear respirator and failure to enforce use of respirators; employee considers respirators superfluous; employee fail to use respirators; plant manager fails to reprimand employee on the use of respirator; and employees inhales organic vapor. These factors will be part of the tier diagram because it is their presence that leads to the resultant accident. According to U.S. Department of Energy (1999) to avoid having to rewrite all the above description of the factors on the chat, assign every factor an alphabetical letter (A, B, C…). These letters will be written of adhesive paper and pasted beside every factor on the ECFA chart. The Tier diagram will have four levels Senior Management, Lower Management, Supervision, Worker Actions and Direct Cause. These will be plotted against the factors characteristics; Causal Factors and Root Cause(s). Afterward the alphabetical letter representing the factors will be noted in the diagram against the level of hierarchy that is responsible. Some factors may appear to various levels of the hierarchy. This should be followed by determining the linkages between the factors in all the tires. The linkages between the factors must be described with a proper statement. The statement becomes a possible causal factor. Also if two factors must be replaced by one factor, they can be replaced by the factor, which may become a root cause. For instance if the relationships point out that fact E and J under worker action are related to factor A under lower management, the E and J under worker action must be replace by A, whereas A becomes part of the root causes. The stamen use to explain this linkage must be put to analysis by a team of investigators who examine it against the criteria for root cause. If it qualifies, it is simplified and a proper report and recommendations created for action (U.S. Department of Energy, 1999).

In sum, tier-diagramming depend heavily on the ECFA chart and uses the events and condition plotted in the chart as the factors for the diagram. In the diagram three things must be noted. First, only the events/conditions that are basic for the occurrence for the accident are used are used (Sklet, 2002); second, the levels affected by the factors must be noted since they are responsible for inhibiting or encouraging the factors; and third, the relationships between the event must be defined since they provide the answer to the root cause (U.S. Department of Energy, 1999).

References

Sklet, S. (2002). Methods for accident investigation. Trondheim: Norwegian University of Science and Technology

U.S. Department of Energy. (1999). Conducting accident investigations: DOE Workbook. Washington, D.C.: U.S. Department of Energy.