Failure Mode and Effect Analysis

We learned over the years that having a great Quality Control program is not enough to assure Reliability and Safety. The most fundamental requirement for any product, is that no single component failure can have a catastrophic effect.  The Failure Mode and Effect Analysis (FMEA) is the Reliability Engineering tool used to examine each component to identify and mitigate the effect of a failure. Some contracts require a FMEA, but the FMEA is usually not done until the design has been completed. 

The failure mode is a function of the part number. In general, each component part number in a system is analyzed to determine its possible failure modes (open, short, mechanical failure etc.). Every part has numerous potential failure modes and theoretically, there is no limit as to the depth one could go. Practically, there is a point of diminishing returns where the added cost exceeds the benefits derived. It is OK to combine similar failure modes if they have the same effect, they can always be separated for finer resolution if necessary in the future. The initial FMEA should include all of the system components that would be repaired or replaced during a maintenance action. Additional components and failure modes should be added as failures occur.

The effect of a part failure depends upon the function of the part in the system. Two valves may have the same part number but the effect of a failure will depend upon what the valve is controlling. Therefore, it is very important that each system component be assigned a unique symbol or designator that is completely independent from the part number. The system schematic is the key document used to determine the effect of a failure of a specific part, in a specific failure mode. The FMEA considers each part and determines the effect that each failure mode will have on the overall system.

The severity of a potential failure is represented by the variable S and is assigned a value between 1 & 10, where 10 is the most severe. The occurrence of the failure (Relative Failure Rate) is represented by the variable O and is assigned a value between 1 & 10, where 10 is the highest failure rate. The ability to detect a failure is represented by the variable D which is assigned a value between 1 & 10 with 10 being the most difficult to detect. The relative importance of a failure modes represented by its RPN number is calculates as RPN = S*O*D.

There are many FMEA software programs on the market today, but most are limited in scope and are very labor intensive. The FMEA methodology is basic to a Forensic Engineering investigation but most Forensic Engineers have a limited staff and have to consider a wide range of potential causes for an incident. Bass Associates, Inc. needed a better way to analyze actual failed systems.  DR-FMEA was developed as an in-house analysis tool to help us to pull together enough information to make a creditable determination as to why a specific failure occurred. We had to consider all factors including Human Error and Code Compliance. DR-FMEA has evolved into the the most powerful FMEA analysis tool available anywhere.

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Bass Associates Inc.
13533 Larkin Drive, Minnetonka, MN 55305
Phone: 952/544-

Copyright 1998 Bass Associates Inc. Last modified: June 25, 2015