Risk Management
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P1/P2 Values RIsk Management
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P1/P2 Values RIsk Management
Does anyone want to talk about P1/P2 values as part of the risk management process?
Some FMEAs include them, some do not, and Im looking to expand/broaden my knowledge on how to interpret risk management files that dont specifically call them out.
Note (Per ISO 14971): Risk = Severity x (P1xP2)
I think the explaination is that:
If you can mitigate P1 (Probability of a Hazardous Situation Occuring), then by default, you eliminate P2 (Proability of a Hazardous Situation Leading to Harm) ever occuring, and therefore P1 is approx = PHarm? But I can also see where there may be instances when P1 > P2 and so the minimum of the 2 values is used as an estimate of the Probability of Harm?
Can anyone help!?
Thanks!
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3 Replies
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Great topic!
I think of Pharm as the overall probability (P1 x P2). This is the same as P value – so in the instances where you don’t see P1 and P2 separately, that’s likely the approach. So, if you mitigate P1 to near 0, pharm will be reduced to the same. But they are not equal.
In my experience, technical mitigations can lower P1 – probably that the hazardous event will occur, but typically leave P2 – probability that hazardous situation will lead to harm – unchanged. This is because once we get to the “hazardous situation” the harm is as likely to occur as it was when P1 was higher. But, if you can change the clinical workflow (maybe adding detections, alarms, workflow safeguards), then you can reduce the probability of P2.
I might have gotten off track lol. But to circle back, I think you could consider the risk score as:
Risk score = P x S, where P is Pharm = (P1 x P2)
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Joe,
Expanding on what Niki wrote, this is an important topic that seems to lead to a lot of confusion and flawed methodology. The P1, P2 probabilities are part of the ISO 14971 risk model but that doesn’t mean they should be explicit columns in a risk table. My recommendation is to make sure that everyone involved in risk assessments understands the P(harm) = P1 x P2 model but that only P(harm) is listed in the risk docs.
I’ve worked on many Risk Management Files under different quality systems over the past 20 years and I’ve seen a lot of mistakes in how P1 and P2 are combined. Simply taking the minimum of P1 and P2 as the P(harm) value is not going to be accurate in all cases. Theoretically it should be a multiplication of the P1 and P2 probability values. Unfortunately, this is not practical because most companies use rankings (e.g., 1 – 5) instead of actual probability values and you can’t multiply the rankings. Some companies use a complex lookup table to derive P(harm) from P1 and P2 rankings but those have to be very carefully designed to not distort the combined probabilities across all ranges. That’s why I think it’s more robust to list only the overall P(harm) in the released risk documents.
There’s a related question here, too, about whether FMEAs should even include Probability of Harm or should be limited to only Probability of Failure but that’s a topic for another thread.
-Aaron
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Really great points, Aaron!
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