Root Cause Analysis
Root Cause Analysis (RCA) is a very important tool in continuous improvement methodologies (eg Lean, Six Sigma, Lean Six Sigma). It examines the factors that cause non-conformance which must be permanently eliminated using a systematic approach and before implementing any process improvement. It is used to select a wide choice of proven approaches, tools and techniques that can address causes effectively. RCA is all about investigating and classifying the root causes into a workable solution and bringing reliability in the system. RCA is designed to help in identification of how an incident happened and at the same time answer why it happened.
Consider the example where an operator who missed the correct operation and did a wrong job, the reason for failure and recommendations such as training the worker on the procedure, reminding all other workers to be vigilant while doing work, and taking extra cautions on the job. Mistakes do occur naturally, but they can be traced back to find out the real causes. Therefore, when we come across issues initial questions are asking the worker for procedure clarity, machines labels, training and so on. The answers to these questions definitely help determine the cause and avert recurrence. A systematic approach should include reviewing the procedure validation and poke-yoke (mistake proofing) to achieve perfection.
The RCA should be done systematically in the following four-steps:
- Team formation: Depending upon the problem and magnitude, form a team to carry out the root cause analysis. The team should have representation from the customer, planning and operations.
- Data collection: Collect data and gather all information to understand the process activities, inputs and outputs. Spend time to associate reasons with the effect.
- Causal factor Analysis: Using the data, cause and effect analysis should be done and contributing factors identified. The causal factor diagram can be made to study logical test that describes the actions leading to the effect.
- Root cause identification: Root causes can be determined after relating the causal factors with the effect. Questions on Why, How, Who, When and Where should further explore the factors that can be concluded as root causes of the problem.
- Recommendations and implementation: Finally after selecting the root causes, the recommended actions and implementation time and responsibility need to be documented.
Root Cause Analysis Tools
Some tools to use in the RCA are 5-whys, fault-tree diagram and root cause map. To perform RCA with 5-whys, we start with the effect or problem and trace backward through enquiring what reason caused the failure. In each question, ask what caused it to happen. This chain of questions keeps on going until we get to the actionable task which is input to a process. The best way to conclude RCA is to get a list of three reasons for each “why”. Also, try to think with the action at the incident and the availability of data to support the evidence. The belief that a complex scenario created the incident will lead to better problem-solving. There can be multiple situations and respective actions that together develop the failure.
Fault tree diagram conducts fault tree analysis to determine the cause of failure and verifies the system reliability using a series of logical base. Based on a visual record that displays the logical relationships between effect and causes drives to the reason for failure. Fault tree diagram can help stakeholders understand the analysis easily and help in understanding design flaws and errors. It helps to prioritize problems and fix the reasons that contribute the highest. Below is an example of a Fault tree diagram for a car accident:
Another tool called Root cause map can help identify the root cause and interpret root cause analysis. Usually problem-solving is seen a puzzling activity and persons doing are not sure about the results in some cases. Root cause map can make a problem clearer as it is done till the basics using a structured diagram and therefore it is easy to learn and straightforward to implement. There are three key principles of in this activity:
- Systems approach to find the root causes and risk mitigation.
- Visual communication to show the team in a structured manner.
- Simple and effective for the team
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