RCM Analysis - Criticality Assessment (Step 2)

This article describes how to complete the Criticality Assessment, the second guided step of an RCM analysis.

The Criticality Assessment answers question five of the seven RCM questions: In what way does each failure matter? It rates the criticality of the failure mode in a no-maintenance scenario.

You set criticality by entering two values: the Probability of failure and the Consequence of failure.

Probability – ETBF

Enter the probability first. Probability is expressed as the ETBF (Estimated Time Between Failures), in years.

You can enter the ETBF in two ways:

• Type a numeric value in years. This is the recommended method.

• Click one of the bands: < 0.5 y, 0.5–4.0 y, 4.0–20 y, or > 20 y. The band enters a fixed ETBF range.

Consequence

Enter the consequence across three categories. Each category supports different levels of detail, and we recommend a specific level for each:

Note

Align the People and Economic consequences in the RCM study's Terms of Reference so that aspects such as flaring, product leakage, and toxic substances are treated consistently across all equipment and failure modes.

Asset

Enter the economic consequence using a Direct, Simple, or Detailed entry. We recommend the Detailed screen because it prompts you to specify the individual repair aspects, which improves the credibility of the assessment.

Note

The financial figure on this screen is the PONC (Price Of Non-Conformance): the cost incurred in a no-maintenance situation.

To carry out the assessment:

1. At the top of the Criticality Assessment Matrix, click Asset.

2. Select type of entry: Direct, Simple, or Detailed.

3. Enter information.

4. Click Save.

People 

Enter the People consequence using a Direct, Simple, or Detailed entry.

To carry out the assessment:

1. At the top of the Criticality Assessment Matrix, click People.

2. Select type of entry: Direct, Simple, or Detailed.

3. Enter information.

4. Click Save.

Environmental

The Environmental consequence only has the Direct entry option.

Direct entry

For any category, you can record a Direct entry by clicking the consequence boxes. If a category has no consequence, do the following:

1. Click Direct.

2. Select Nothing.

3. Click Save.

If you want to see the full Criticality Assessment Matrix, click Overview.

Note

When using the Direct Entry method, RCM uses the mid-point (logarithmic scale) between the lower and upper bounds of the selected interval.

Once you are done, click Strategy Decision Tree to continue to the next guided step(opens in new tab).

Instruction Video

For a walkthrough of the guided steps, see RCM Analysis Guided Steps - Episode 7. 

Background: the Criticality Matrix

A Direct entry on a consequence category derives the Price of Non-Conformance from the average of the category's boundary values. The boundary values are 10⁵, 10⁶, 10⁷, and 10⁸. For example, the Low category averages 10⁵ and 10⁶ — that is 10⁶·⁵, or about 316 k$. The other middle ranges follow the same method.

The Negligible scale is a special case. Its lower bound is shown as 0 but actually represents the 10–999 range (a logarithmic scale cannot start at 0). Taking the average would place the value around 31.6 k$, which is too high for this scale, so the Negligible Direct-entry value is fixed at 10 k$ instead. The Extreme scale has the same characteristic at its upper end, but it is rarely used and so has little practical impact.

Note

The consequence scale of the Criticality Matrix is denominated in US dollars and is not adjusted for currency changes.

In RCM we recommend Detailed entries for Asset, and Direct entries for People and Environment.