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Consequence Priority Concepts and Examples

One of the outputs of a prioritization analysis is the asset’s consequence priority number. The priority number is determined by comparing an asset’s failure consequence scores to a set of rules. These rules are defined at the same time as the analysis criteria.
The priority ranking is used as a multiplier with the alarm severity to determine if an indicator alarm is pushed up the hierarchy to the parent assets. In the Indicator Settings, you must enter the minimum alarm notification ranking that is needed to alert parent assets. The alarm notification is calculated by multiplying the alarm severity ranking with the consequence priority number. For example, with critical alarm (alarm severity 10) and priority ranking of 5, the alarm notification ranking would be 50 (10 x 5 = 50). If your site minimum alarm notification for pushing up the hierarchy is set for 60, this alarm would not be visible higher up the hierarchy.
The priority ranking is also used to prioritize work activities. In many maintenance systems, this is also called the “criticality” of the asset. For example, you would usually perform maintenance on an asset with priority 9 before one with priority 2.
However, when the priority numbers are close together (for example, 4 and 5) it can become difficult to distinguish any difference. Therefore, it is important to review the nature of the failure mode and consequences. For example, you might have two requests: one to paint the exterior of a chemical tank with priority 9, and one to calibrate a measurement system with priority 6. In this case, the calibration might have a higher urgency than the chemical tank painting.
Note: Good practice limits the number of priority numbers to no more than nine and typically no fewer than five. With too many numbers, the meaning becomes ambiguous. With too few, it is difficult to make decisions based on that number alone.
An asset’s priority number is determined by comparing the asset’s scores for each criterion to rule clauses. For example, the highest priority rating of 9 has the analysis rule “If safety or environment >/= 38, then priority equals 9.” You can also use rule statements that sum several criterion scores or just compare to the maximum criterion score an asset attains.
To illustrate how consequence priority numbers are determined, consider the following priority number rules.
Priority Number
Rules
9
The asset’s safety or environmental consequence scores are equal to or greater than 38
Or, the sum of the asset’s quality, throughput, customer service, and operating cost consequence scores are equal to or greater than 38
8
The asset’s safety or environmental consequence scores are equal to or greater than 28
Or, any one of the asset’s quality, throughput, customer service, and operating cost consequence scores equals 10
The following assets have been analyzed and given the scores shown:
Criterion
Asset 1
Asset 2
Asset 3
Asset 4
Safety
40
20
20
0
Environment
20
38
20
0
Quality
0
0
10
10
Throughput
0
0
8
0
Customer Satisfaction
0
0
10
0
Operating Cost
4
4
10
0
The priority numbers assigned to these assets are:
Asset
Priority Number
Asset 1
9
Asset 2
9
Asset 3
9
Asset 4
8

Explanation

Asset A1 is assigned a priority number of 9 due to its safety consequence score of 40. This meets the equal to or greater than 38 rule for this priority.
Asset A2 is also assigned a priority number of 9, in this case due to its environmental score of 38.
Asset A3 would also be assigned a priority of 9. While its safety and environmental consequences are low (relatively speaking), the sum of its remaining consequences total 38. This meets the second rule for assigning an asset a priority of 9.
Asset A4 would be assigned a priority of 8 due to its high score for quality.