Predefined trees investigation tools

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. 

Some predefined trees do fully reach down to the root cause level. A system test should be applied to each identified root cause to ensure that it relates to a management system failure. By applying the 5-AAdiys tool to each cause identified at the end of the relevant branches of the tree, the investigator can determine if another underlying cause can be identified. 

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. 

The MORT technique has received domestic and international recognition, and has been applied to a wide range of projects from investigation of occupational incidents to hazards identification. It is supported by detailed documentation, and has been subjected to continued development efforts since it was originally introduced. Today there are several predefined trees available from public and proprietary sources that are based, at least in part, upon tbe MORT tool. 

---