Explain in detail fault tree analysis and human error analysis
Answer:-
Fault tree analysis
A Fault tree analysis is a deductive reasoning method that focuses on one particular event and provides a method for determining basic cause of that event. This method is used to identify combinations of equipment failures and human errors that can result in accident or an initiating event. FTA allows the safety analyst to focus on preventive measures on these basic causes to reduce the probability of an accident.
Symbols used in fault tree construction:
Steps in Performing Fault Tree Analysis (FTA):
- Problem Identification:
- a) Define the Top Event: Identify the main accident event or failure that you want to analyze.
- b) Define Analysis Boundaries: Establish the boundaries of the analysis, including the scope of events to be considered, the physical boundaries of the system, the level of detail required, and any assumptions made.
- Fault Tree Construction:
- Start with the top event and work downwards, using logical symbols such as “OR” and “AND” gates. Continue breaking down the events into their basic causes, level by level, until all contributing factors are identified.
- Fault Tree Solution:
- Analyze the completed fault tree to understand how different equipment failures and other factors interact to potentially cause the top event. Use methods such as matrix analysis to identify minimal cut sets, which represent the smallest combinations of basic events that can cause the top event. This allows for ranking and quantification if failure data is available.
- Minimal Cut Set Ranking:
- Minimal Cut Set Analysis: This mathematical technique identifies all combinations of basic events that can lead to the top event. Minimal cut sets are those combinations that contain the smallest number of events necessary to cause the top event.
- Ranking: Rank the minimal cut sets based on their significance. Single-event minimal cut sets are considered more critical than multi-event ones because a single event is more likely to occur. Additionally, rank human errors as more significant than active equipment failures, and active failures more critical than passive failures.
The figure below shows the process of fault tree analysis.
Fault tree should be completed in levels and each level should be completed before beginning the next level.
The below examples depicts that causes B1,B2,B3,B4 and B5 are the basic events, which can lead to top event T, which is “No light in room on demand” and the mathematical expression for the top event is
T=G1’G2
= (B1+B2)’ (B3+B4+B5)
= B1B3+B2B3+B2B4+B1B5+B2B5 (6 minimal cut characters)
This indicates the occurrence of either of basic events B1 or B2 along with occurrence of any of the basic events B3, B4 and B5 would lead to top event T.
Human Error Analysis (HEA):
Human Error Analysis is a systematic method used to predict potential errors and human failures that might occur during task performance. Its primary goal is to identify and mitigate hazards before they lead to accidents, rather than just analyzing past incidents. Records of past accidents can help identify trends and predict potential issues, but HEA is proactive in nature.
Two Approaches to HEA:
1] Task Analysis Approach:
- Observe employees at work and identify hazards by analyzing the tasks they perform.
- This involves understanding the steps involved in a task and noting where errors are likely to occur.
2] Job Performance Approach:
- Perform the job task yourself to gain firsthand experience and identify hazards.
- This approach helps in understanding the practical challenges and potential errors associated with the task.
Integration with Other Methods:
- It is beneficial to conduct HEA in conjunction with other methods such as Failure Modes and Effects Analysis (FMEA) and Hazard and Operability Studies (HAZOP). This integrated approach enhances the overall effectiveness of identifying and mitigating risks.