Some of the confusion around FMEAs (Failure Modes Effects Analysis)

Do you struggle with FMEA or FMECAs? Here are some thoughts that might help add clarity. If you disagree please reach out and lets discuss and learn together.

Function: In the context of FMEA, a function is the intended operation or performance of an item or system, typically defined by its performance standards or specifications. Essentially, it's the reason the item exists or what it is designed to do.

 

Example: In the case of a car brake system, one of its functions could be "to decelerate the vehicle to a stop when the brake pedal is applied".

 

Functional Failure: A functional failure is the inability of a system or component to perform its intended function. It is the state where the function of the system or product is lost or diminished.

 

Example: Following the above example, a functional failure of the car brake system could be "the vehicle does not decelerate to a stop when the brake pedal is applied".

 

Failure Mode: A failure mode is the specific way in which an asset or a system fails or ceases to perform its intended function. It's the end result or manifestation of a failure.

 

Example: A failure mode of the car brake system could be "brake fluid leakage".
Failure Mechanism: Failure mechanism is the "how" or the process that leads to the failure mode. It's the physical, chemical, or other processes that result in failure.

 

Example: A failure mechanism for the car brake system, leading to the failure mode of "brake fluid leakage", could be "corrosion of the brake lines", which over time weakens the lines and allows brake fluid to escape.

 
Functions are applied at the asset.

Supporting or secondary functions can be at the asset level but are typically at the subsystem level.

Failure modes, effects, and RPN are assigned to the component level. 

Risk Priority number would then be driven by:

functional failure would drive the majority of Severity and Occurrence scores and failure mechanism would drive the detection score

Failure mechanisms would represent the root causes at a physical or human level and thus the corrective action or inspection task should be driven by the failure mechanism.

 

Failure Effects are how the failure may make itself known to a Human.

 

In the case that a failure mode does not drive a failure effect, then there likely is not an associated functional failure.