How the score works
Each asset is rated 1 to 5 on six factors. Each rating is multiplied by its factor's weight, summed, and scaled so the highest possible score is 100. That keeps scores comparable when you change the weights.
Rating the factors
| Factor | 1 means… | 5 means… |
|---|---|---|
| Safety | No credible injury risk if it fails | Failure could cause serious injury |
| Environment | No release or compliance impact | Reportable release or permit breach |
| Production | No effect on output | Stops a line, building, or critical service |
| Repair cost | Minor parts and labor | Major cost or long-lead parts |
| Redundancy | Installed spare takes over automatically | No backup — nothing runs while it's down |
| Failure history | Rarely or never fails | Fails often |
These anchors are a general starting point. Before scoring, agree as a team what each number means at your site — "serious injury" and "long-lead" should have concrete definitions, not opinions.
Why a safety override?
Weighted scores can bury a safety-critical asset that's cheap, redundant, and rarely fails. If its failure could still seriously hurt someone, it deserves Class A attention anyway. The override (on by default) makes sure any asset rated 5 for safety or environment lands in Class A.
What to do with the classes
A common pattern — not a standard — is to give Class A assets the most rigorous strategy: condition monitoring where it fits, critical spares on hand, and FMEA-based PM plans. Class B gets time-based PMs and standard spares. Class C may be run-to-failure where that's genuinely safe and cheap. The thresholds (70 and 40 by default) are a rule of thumb; adjust them until the A list is short enough to actually act on.
FAQ
Is there an official criticality standard?
No single standard prescribes a criticality formula. ISO 55001 requires asset management decisions to be risk-based, and most organizations meet that with a weighted scoring or risk-matrix method like this one. If your company has a corporate risk matrix, match the factor definitions to it.
How many assets should be Class A?
There's no fixed rule, but if most of your assets are Class A, the ranking isn't helping you prioritize. Raise the A threshold or revisit how ratings are being applied.
Where is my ranking saved?
Only in this browser on this device. Nothing is sent to a server. Export to CSV to keep a copy or load the results into your CMMS.
Sources & standards
- International Organization for Standardization. ISO 55001: Asset management — Management systems — Requirements. — Requires risk-based asset decisions; does not prescribe a scoring formula.
Factor anchors, default weights, and class thresholds are a rule of thumb from the author. Align them with your organization’s own risk matrix.