Failure Mode Details – Failure Finding Interval

The Failure Finding Interval popup allows you to enter data to determine the failure finding interval (FFI) for the selected failure mode. Typically, you would only enter a failure finding interval for hidden failure modes and only when the selected Control Method indicates this, meaning it has Failure Finding selected. The popup caption will be different if the selected Control Method is for a failure finding task or not, or if no Control Method is selected yet.

However, the system, will always let you enter data on the popup. The following important attributes are available on this popup:

1. Failure Finding Interval: This field is protected and automatically calculated unless you select the Manual Entry checkbox.

2. UOM: The unit of measure of the FFI. For example, weeks, months, years, etc.

3. Manual Entry: Select this to enter the FFI manually if you have your own method to calculate FFI.

4. Failure Finding Interval Note: Free text field for relevant notes.

5. And the following variables that are used to calculate the FFI in a system that uses 1 or more redundant protective parallel devices. Note that each protective device, on its own, must be capable of preventing the multiple failure consequences of the hidden failure mode.

   1. MTBF Multiple Failures (MMF)

   2. MTBF Protected Function (MTED)

   3. MTBF Protective Device (MTIVE)

   4. Redundant Protective Parallel Devices (N)

Example: A nearby Hospital needs to calculate FFI for a maintenance task plan on their emergency standby diesel power generator. The local power utility states that an extended power outage occurs in the hospital area once every 2 years. The backup diesel generator manufacturer says their product fails to work once every 100 yrs. When the hospital’s chief administrator is asked how often she tolerates both a power outage and a generator failure, happening simultaneously, she answers: “NEVER!” Of course, she’s reminded zero risk is unattainable, so she offers: “Once in a million years!”

Now, from the above, it can be shown that…

• MTBF Multiple Failures (MMF) = 1,000,000 years

• MTBF Protected Function (MTED) = 2 years

• MTBF Protective Device (MTIVE) = 100 years

• Redundant Protective Parallel Devices (N) = 1 (there is only 1 standby generator)

Using these variables in the following formula gives an FFI of 0.0004 years which is equal to 3.5 hours.

This means that using only 1 emergency standby generator requires the hospital staff to test the system every 3.5 hours to give the confidence that it will work when needed. Because this test frequency is impractical (and may even cause the standby generator to fail), another option is to add another identical diesel generator alongside the first one. This makes the Redundant Protective Parallel Devices (N) = 2.

Now, with 2 in parallel, the system calculates an FFI of 0.244949 years which is equal to 89.4 days. Obviously a much more practical solution than before.

This popup can be accessed from the Failure Modes popup on the RCM tab, the RCM Failure Mitigation tabs on the Equipment and RCM Templates screen and from the Failure Modes and Failure Mitigation tabs of the Case Management screen.