How do you calculate a contamination risk score?

Weight the three inputs: severity times 0.40, plus likelihood times 0.35, plus detection difficulty times 0.25. With severity 9, likelihood 4, and detection 5, the score is 3.6 + 1.4 + 1.25 = 6.25.

Why is severity weighted highest?

A high-severity contamination — free iron on a stainless implant or media embedded in a fatigue-critical peened surface — can cause field failure regardless of how often it happens. At 40% weight, the severity-9 input contributes 3.6 of the 6.25 total in the example, dominating the score.

What is a good contamination risk score?

On a 1-10 scale, under 3 is generally acceptable, 3-6 warrants added controls, and above 6 should trigger mandatory verification like coupon testing or passivation. The example's 6.25 sits right at the threshold where extra controls become non-negotiable.

How do I rate detection difficulty?

Score it high when contamination is invisible to routine inspection — embedded media you can't see, free iron needing a ferroxyl test, or oil that only shows under UV. Low scores mean obvious, easily caught defects. The default 5 reflects contamination needing a specific test to confirm.

Risk score vs a full FMEA RPN — what's the difference?

A classic RPN multiplies severity, occurrence, and detection, which inflates and distorts rankings. This weighted-sum approach keeps the score on the same 1-10 scale as the inputs and reflects that severity matters most, making thresholds easier to set and defend.

How do I lower a contamination risk score?

Attack the largest weighted term first. You usually can't change inherent severity, so cut likelihood with media segregation and clean air, and cut detection difficulty by adding ferroxyl or UV checks that catch what visual inspection misses.

Abrasive Blasting, Shot Peening & Surface Prep calculator

Surface Contamination Risk Score Calculator

Surface contamination risk score is a weighted index that rates how dangerous abrasive or process contamination is on a given part — embedded media, free iron from steel grit on stainless, oil carryover, or a coating that hides defects. Quality engineers in blasting and shot-peening shops use it to triage which jobs need extra rinse, passivation, or coupon verification before parts move on. It matters because contamination failures often surface late — a peened landing-gear part or a stainless weldment can pass visual and still fail in service. By weighting severity most heavily, then likelihood, then how hard the contamination is to detect, the score points limited inspection resources at the jobs that can actually hurt you.

What this calculator does

Score the risk of coating or peening contamination using severity, likelihood, and detection difficulty.
a quality inspector needs a practical contamination risk screen before coating, bonding, or peening acceptance
It computes a single weighted contamination risk score from severity (40%), likelihood (35%), and detection difficulty (25%).

Formula used

Contamination risk score = severity × 0.40 + likelihood × 0.35 + detection difficulty × 0.25

Inputs explained

Contamination severity:
Contamination likelihood:
Detection difficulty:

How to use the result

Use it during process FMEA or job planning to flag which blast and peen jobs need enhanced cleaning, passivation, or verification.
Scores are relative judgments, not measured contamination levels; calibrate the 1-10 inputs against a shared rubric or different estimators will produce inconsistent results.

Common questions

How do you calculate a contamination risk score? Weight the three inputs: severity times 0.40, plus likelihood times 0.35, plus detection difficulty times 0.25. With severity 9, likelihood 4, and detection 5, the score is 3.6 + 1.4 + 1.25 = 6.25.
Why is severity weighted highest? A high-severity contamination — free iron on a stainless implant or media embedded in a fatigue-critical peened surface — can cause field failure regardless of how often it happens. At 40% weight, the severity-9 input contributes 3.6 of the 6.25 total in the example, dominating the score.
What is a good contamination risk score? On a 1-10 scale, under 3 is generally acceptable, 3-6 warrants added controls, and above 6 should trigger mandatory verification like coupon testing or passivation. The example's 6.25 sits right at the threshold where extra controls become non-negotiable.
How do I rate detection difficulty? Score it high when contamination is invisible to routine inspection — embedded media you can't see, free iron needing a ferroxyl test, or oil that only shows under UV. Low scores mean obvious, easily caught defects. The default 5 reflects contamination needing a specific test to confirm.
Risk score vs a full FMEA RPN — what's the difference? A classic RPN multiplies severity, occurrence, and detection, which inflates and distorts rankings. This weighted-sum approach keeps the score on the same 1-10 scale as the inputs and reflects that severity matters most, making thresholds easier to set and defend.

Last reviewed 2026-05-12.