Confusing Failure Modes with Failure Mode Causes -

Confusing Failure Modes with Failure Mode Causes

Here is a letter published in ASQ monthly journal ‘Quality Progress‘ by SQT CPI Tutor Albert Plant:

In response to “Narrower Focus” (January 2015, pp 23-28); I believe the author may be confusing failure modes with the causes of the failure modes.

The author talks of the difficulty of selecting failure modes from a nearly infinite universe. This may apply to the failure mode cause, but not the selection of the failure mode itself. In my view, the identification of the failure mode is quite straight forward. For a well-defined process step, the number of failure modes is unlikely to exceed two or three. The potential failure mode is the manner in which the process step could potentially fail to meet the process requirements. The identification of the failure mode can be greatly facilitated by detailing the specific requirements of the process step.

Consider the article’s example of drilling a hole referred to in the article. The requirements for the process step may state that the hole depth is to be 20 mm +/- 0.5 mm. There are just three potential failure modes in this case; the hole is too deep, the hole is not deep enough, or the hole is not drilled. I don’t think the statement of the failure mode should contain actions such as “drilled hole too deep”. I believe that actions belong with the causes of the failure mode.

Albert Plant
Waterford, Ireland