Difference between revisions of "Fault Tree Analysis"

Revision as of 01:55, 23 April 2024

Fault Tree Analysis

Fault tree analysis is a form of probabilistic risk assessment 1 2 that studies a specific system, process, or device failure using a hierarchical tree diagram. The top event is broken down into increasing levels of granularity to identify the source of a system or process failure’s root cause. The fault tree is a graphical representation of the failure and its preceding events and can be used in a multidisciplinary setting to discuss process failures in healthcare settings. Probabilistic risk analysis (PRA) has become an acceptable safety management tool in healthcare settings. 1 Fault tree analysis has been used in medical device failure evaluation 3, medication errors, medical omissions 4, wrong site surgery evaluation 5, anesthesia failures 6, and as a method for root cause analysis7 probabilistic risk assessment in process and system failures. 1 6 8 Fault tree analysis can be used as a predictive model or used retrospectively to identify system failures. When used retrospectively, the technique works backwards from the failure to basic, fundamental events. The basic events are then linked by Boolean logic gates.

A fault tree is created using the following steps: 9

1. Identify the process or system to be studied to assign the top event

2. Identify the events in hierarchical levels of granularity

3. Create a flow diagram

4. Determine how the events are related

5. Link the events using Boolean logic gates

6. Events occurring together are linked by “AND” gate

7. If either event occurring will lead to the top event, use an “OR” gate

8. Classify causes of failure

9. Repeat steps for each event that is not considered a basic event

10. Calculate the probability of multiple events occurring and leading to the top event

11. Analyze the fault tree and improve the model

12. Form a multidisciplinary team to evaluate the fault tree. Multiple iterations may be necessary if all contributing events were not considered.

13. Form a multidisciplinary team to discuss the prevention of system failures. Focus on events that are preventable or events that occur with the highest probability to mitigate risk. 9

Boolean Logic Gates

       AND Gate is used to calculate the probability of both events occurring
       Po = Pa x Pb

OR Gate is used to calculate the probability of either event occurring

Po = (1-(1-Pa) x (1-Pb))

The advantages of using the fault tree analysis 9

• Aids in the identification of possible system failures and their associated events or causes

• The analysis can be used to evaluate multifactorial failures

• The analysis can be used to document risk mitigation efforts and be used in quality improvement activities 1 6 2

• The analysis can be used as a teaching tool 3 6

• This method can be used as an analysis summary 6

• Fault trees can be used as a predictive model or as a retrospective analysis

• This graphical method facilitates a multidisciplinary group discussion. The assessment of the probability of events occurring can be displayed in a graphical hierarchical method. This allows the team to focus on failures that are most likely to occur or that are preventable.

Disadvantages of fault tree analysis

• Diagrams can be complex

• Diagrams are limited by Boolean logic

• Probability data may not be available

• Events can become granular

• The fault tree is subject to the creating analyst’s bias

• An individual’s error may be revealed to the group during the analysis

References: 1. Wreathall J, Nemeth C. Assessing risk: The role of probabilistic risk assessment (PRA) in patient safety improvement. Qual Saf Health Care. 2004;13(3):206-212. doi:10.1136/qshc.2003.006056

2. RISK MODELLING WITHIN HEALTH CARE: ANALYZING PROCESSES. www.qshc.com

3. Hyman WA, Johnson E. Fault Tree Analysis of Clinical Alarms.

4. Rogith D, Satterly T, Singh H, et al. Application of Human Factors Methods to Understand Missed Follow-up of Abnormal Test Results. Appl Clin Inform. 2020;11(5):692-698. doi:10.1055/s-0040-1716537

5. Abecassis ZA, McElroy LM, Patel RM, Khorzad R, Carroll C, Mehrotra S. Applying fault tree analysis to the prevention of wrong-site surgery. Journal of Surgical Research. 2015;193(1):88-94. doi:10.1016/j.jss.2014.08.062

6. Culwick MD, Endlich Y, Prineas SN. The Bowtie diagram: A simple tool for analysis and planning in anesthesia. Curr Opin Anaesthesiol. 2020;33(6):808-814. doi:10.1097/ACO.0000000000000926

7. Martin-Delgado J, Martínez-García A, Aranaz JM, Valencia-Martín JL, Mira JJ. How Much of Root Cause Analysis Translates into Improved Patient Safety: A Systematic Review. Medical Principles and Practice. 2020;29(6):524-531. doi:10.1159/000508677

8. Taitz J, Genn K, Brooks V, et al. System-wide learning from root cause analysis: A report from the New South Wales Root Cause Analysis Review Committee. Qual Saf Health Care. 2010;19(6). doi:10.1136/qshc.2008.032144

9. https://www.ahrq.gov/ncepcr/communities/pbrn/index.html#ref-3. AHRQ website.

Submitted by Jennifer Glance