1. Risk Assessment: A Practical Guide to Assessing Operational Risk
Chapter 8:
Failure Mode and Effects Analysis
9/20/2018

2. Failure Mode and Effects Analysis
Objectives
Introduction, Overview and Background
Purpose and Use
Practical Application
Examples
Practice Exercises/Questions
9/20/2018

3. FMEA Introduction
Failure Mode and Effects Analysis (FMEA) is one of the most commonly used techniques for hazard analysis and risk assessment.
FMEA is used to identify and analyze the ways in which system components can fail to fulfill their designed intent, and the resulting effects to the system. To state plainly, FMEA focusses on failures and their effects to understand how each failure can be prevented and their effects reduced.
FMEA is generally considered a qualitative or semi-quantitative method that lists systematically the failure modes, their effects, existing safeguards, and any additional controls that are needed to reduce risk to an acceptable level.
9/20/2018

4. FMEA Historical Prospective
FMEA, one of the first failure analysis methods, was developed by the United States (U.S.) Department of Defense (DoD) in It was originally published in the Military Procedure, MIL-P Procedures for performing a failure mode effect and critical analysis, and its objective was to classify possible failures related to personnel and equipment.
Later, the methodology was used by National Aeronautics and Space Administration (NASA). During the 1960s.
FMEA was successfully used by the nuclear industry and space exploration programs.
The U.S. automotive industry adopted FMEA methodology in the late 1970s.
Numerous standards and publications addressing FMEA were issued since the initial MIL-P-1629 standard was published.
9/20/2018

5. FMEA similar method
A similar method which incorporates an additional step of performing a formal criticality calculation is called Failure Mode Effects and Criticality Analysis (FMECA).
FMECA was developed by NASA to improve and verify the reliability of space program hardware.
FMECA requires objective data to support its criticality analysis and calculation, as well as more detailed risk-ranking information, and is not specifically covered in this text.
9/20/2018

6. FMEA - US and international standards
FMEA is included in many US and international standards.
The International Standards for Organization (ISO) 31010:2009 and American National Standard Institute ANSI/ASSE Z Risk Assessment Techniques standard suggests using FMEA as one of the risk assessment techniques.
In addition, FMEA is one of the eight risk assessment techniques listed in the American National Standard, ANSI/ASSE Z , Prevention through Design, Guidelines for Addressing Occupational Hazards and Risks in Design and Redesign Processes. The ANSI Z590.3 standard states that FMEA, along with Preliminary Hazard Analysis (PHA), and What-If methods are sufficient to address most risk situations.
9/20/2018

7. Purpose and Use
A FMEA is performed to review the defined system’s components individually to identify failure modes, causes and effects of such failures on the system.
FMEA purpose is to identify the ways in which systems, components or processes may fail, and the effect the failure may have on the system and users.
FMEA is frequently used as a first step of a system reliability study or product development. It is also used in many different applications. According to the ISO 31010/ANSI Z690.3 Risk Assessment Techniques standard there are different FMEA applications:
Design or product FMEA – used for components or product design
System FMEA – used for an entire system
Process FMEA – used for manufacturing, assembly or other process
Service FMEA – used for installation or service of equipment during operation
Software FMEA – used for software systems and controls
9/20/2018

8. Other FMEA types
Human Factors FMEA – used for interactions between users and equipment;
Concept FMEA – a condense version used for analyzing alternative concepts;
Hazard Analysis – used for systems throughout their life-cycle to analyze safety-related risks;
Failure Mode Effects and Diagnostic Analysis (FMEDA) – used as an extension of FMEA to systematically diagnose failures and effects; and
Failure Mode Effects and Critical Analysis (FMECA) – used as an extension of FMEA so that each fault mode identified is ranked according to its importance or criticality.
9/20/2018

9. FMEA Limitations
FMEA is only used to identify single failure modes or hazards and does not address synergetic effects from multiple hazards.
It may be time consuming and costly.
FMEA may be difficult to use for complex multilayered systems.
Generally, does not address consequences of the listed hazards.
FMEA usually requires additional follow-up analyses or utilization of more complex risk assessment techniques.
9/20/2018

10. FMEA can be used to:
assist in selecting design alternatives with high dependability
ensure that all failure modes of systems and processes, and their effects on operational success have been considered
identify human error modes and effects
provide a basis for planning testing and maintenance of physical systems
improve the design of procedures and processes
provide qualitative or quantitative information for analysis techniques such as fault tree analysis
9/20/2018

11. FMEA Example Worksheet
Potential Failure Mode and Effects Analysis Sequence (Informative) - reprinted with permission from ANSI/ASSE Z (Courtesy of the American Society of Safety Engineers)
9/20/2018

12. Defining Failure Modes
A clear meaning of a “failure mode” is necessary for those using FMEA and other failure analysis techniques.
ANSI Z590.3 defines failure mode as “what is observed to fail or to perform incorrectly”. The standard further describes failure mode considerations as follows:
“The possible failure modes that could result in hazardous situations shall be considered, including the reasonably foreseeable uses and misuses of facilities, materials, and equipment.
Credible circumstances that could arise that would result in the occurrence of an undesirable incident or exposure shall be identified. Determine how and under what circumstances this situation could be harmful.”
9/20/2018

13. Risk Description Considerations
The FMEA technique is designed to identify failures and their resulting risk exposures making the risk descriptors and scoring system vital to an effective analysis. Many risk level scoring models are available ranging from basic two factors systems to more complex risk factor systems including four or more variables. These risk descriptors often used in FMEA and other risk assessments include:
Severity of Consequence (S)
Occurrence Probability (O)
Frequency of Exposure (E)
Detection of Failure (D)
Prevention Effectiveness (PE)
Risk Priority Number (RPN)
9/20/2018

14. Risk Description
The ANSI Z590.3 Prevention through Design standard presents a two factor scoring system with risk codes for the severity of consequences (S) , and occurrence probability (P).
In many FMEA models, a third factor, ‘detection of failure’ (D) is used in the risk level scoring system.
In other applications, where hazard control measures are analyzed, the use of ‘prevention effectiveness’ (PE) is used in place of detection. Prevention effectiveness is an estimate of a control measure’s efficacy in controlling the failure and its effect, and is determined according to the hierarchy of control model found in ANSI Z590.3 and other safety standards.
9/20/2018

15. RPN
As described by ANSI Z560.3, the risk priority number (RPN) is a semi-quantitative measure of criticality obtained by multiplying numbers from rating scales (usually between 1 and 10) for consequence of failure, likelihood of failure and ability to detect the problem. (A failure is given a higher priority if it is difficult to detect.)
There are other models suggesting a four variable scoring system including severity, probability, frequency of exposure and detection. The use of three and four risk factors systems should be carefully examined. A four factor risk scoring system can be problematic.
Fred Manuele presents a hypothetical scenario of a fatality that is obviously an unacceptable risk; however, when applying a four factor risk score, it is rated as acceptable. This occurs due to a dilution of severity by the other three factors through the mathematical scoring giving each risk factor a weighting of 25%.
9/20/2018

16. RPN Cont.
In a three factor risk scoring system of severity, probability, and frequency of exposure, the severity factor is also ‘discounts’ in the final score. With three factors in the equation, each has a weighting of 33% of the final risk score as shown below.
Severity x Probability x Frequency of Exposure = Risk
To more accurately score risk levels, Manuele suggests that severity receive a weighting of 50% to reflect the impact severity has on incident outcomes as shown below.
Severity x (Probability + Frequency of Exposure) = Risk
9/20/2018

17. High severity/Low probability events
To systematically reduce the potential for high severity/low probability events, it is necessary to concentrate on preventive measures, and specifically the strength of the risk control measures or barriers. Risk professionals can essentially “borrow” ideas and methodologies from other industries such as the Food Processing industry. An example of a modified CCP decision making model is presented here:
9/20/2018

18. Figure 8.3 illustrates the CCP decision tree process steps taken.
9/20/2018

19. FMEA risk level scoring system
Various organizations may use different rating scales based on customer or project requirements, however, it is important that consistent evaluation rating criteria be applied. Rating criteria should be standardized so that a lower RPN value indicates a lower risk level.
Using a 5 point risk assessment scale for three variables will result in a RPN between 1 and 125. This calculation is displayed below:
Risk Priority Number = Severity x Probability x Prevention Effectiveness
Severity: 1-5 scale.
Where:
1-Insignificant
2-Negligible
3-Marginal
4-Critical
5-Catastrophic
Probability /Occurrence, 1-5 scale. Where:
1-Unlikely
2-Seldom
3-Occasional
4-Likely
5-Frequent
Prevention Effectiveness: scale.
Where:
Avoid, eliminate, substitute;
Engineering control;
Warning, administrative;
PPE;
None
9/20/2018

20. FMEA Process Steps
Figure 8.5 FMEA Process. Source: “Failure Mode and Effects Analysis (FMEA): A Guide for Continuous Improvement for the Semiconductor Equipment Industry,” SEMATECH Technology Transfer # B-ENG. Reprinted with permission.
9/20/2018

21. Failure Mode and Effects Analysis Example
9/20/2018

22. FMEA Practical Application
Specifically, hazards are identified and recorded in “Process Operation, Function or Purpose” column so that the risks arising from those hazards can be evaluated and determined if they are acceptable or not. Hazards include all aspects of technology, human factors and activity that produce risk. Hazards can be physical, biological, chemical, mechanical, psychosocial, etc.; risks can be focused on the health and safety of the worker, property or the environment.
The example (next slides) is a FMEA used to evaluate potential hazards during rebar operations performed in concrete construction.
9/20/2018

23. FMEA Hazard Analysis Example
9/20/2018

24. FMEA Current State Risk Example
9/20/2018

25. FMEA Future State Risk Example
9/20/2018

26. FMEA Summary
FMEA is applicable to human, equipment and system failure modes as well as software, hardware or processes. It also presents failure modes, causes and effects in systemic and easy to read format highlighting the highest RPNs.
FMEA relies on professional judgment and semi-quantitative methods to assess the significance of hazards and assign a ranking to each task or process.
Utilizing FMEA helps in prioritizing recommendations for reducing risks.
9/20/2018

27. Summary
FMEA is flexible enough and it may be applicable to any process, new product design or a system.
FMEA may be used as a high-level analysis early in the design phase of the project or detailed risk assessment of low level processes or systems.
The quality of the analysis depends mainly on the knowledge of the team members, quality and availability of documentation, the expertise of the safety leader and the management of the organization.
9/20/2018