HRST developed an upgraded criticality matrix assigning a criticality value that matches the reality of the severity and occurrence for boiler-related events that commonly occur in powerplants and process steam plants.

HRST uses a four by four matrix to describe criticality. Four bins offer distinct, meaningful categories for both severity and occurrence. In a four category criticality matrix, the values 1-4 mark the top ranges of each severity and occurrence bin. In order to more accurately portray the relative degree of the various values for Severity and Occurrence, the center point for each of these bins is used. The center points for a four–bin spread are 0.5, 1.5, 2.5 and 3.5, as shown below.

In order to avoid fractional values, these numbers are doubled to 1, 3, 5 and 7 for the criticality matrix determination. Findings are assigned a degree of Severity (S) and Occurrence (O) based on this 1, 3, 5, 7 scale, with 7 being highest. The Criticality for each finding is a product of the Occurrence and Severity, resulting in the following Criticality matrix.

The resulting preliminary criticality matrix provides a scale of 1-49 for criticality, with 49 being most critical. We call this matrix preliminary, but it does underlie the final matrix used in our reports. Two further adjustments are made to finalize the matrix:

  1. The 1-49 scale is normalized to a scale of 1-100.
  2. The Severity and Occurrence “index numbers” are revised to match the Severity and Occurrence scales currently used by HRST, where a ”1” represents the greatest degree of Severity and the highest probability of Occurrence.

This results in the final criticality matrix used in HRST’s reports, which is reproduced below:

The criticality of each finding corresponds with a priority ranking, indicated by the colors in the matrix above. The priorities are assigned to the recommendations to guide repair timelines. The time frame associated with each priority is described in the table below:

Priority of Findings

For items that are considered good practice but are not necessarily critical, in that they won’t lead to an immediate problem causing damage, safety risk, or economic impact, a priority of 2 is assigned to the finding without any criticality.