Risk Management ISO 14971 - Probability of Occurrence

[Tidge]

P1 is the "probability of Hazardous Situation"? How do you get the number for probability? Except it may be from the ISO/TR 24971:2020 Table 5. How to explain the number for probability while the third party auditor asks me?

P1 (and P2) are almost universally treated as a qualitative assessment (something like minor/moderate/major possibility of the hazardous situation existing; it is possible to also include a "zero" possibility but typically folks simply don't include lines-of-analysis for "obvious" non-existing hazards). As long as the same qualitative assessment is applied across hazards, there is really not much to explain... at least as far as application.

These aren't a quantitatve "number" they area relative rankings used in a categorization scheme.

Sidebar: If the P1 for some risk is generally recognized as having "major probability" of existing, there is likely a consensus standard that exists and we (in the industry) start thinking about these risks as affecting "basic safety". This is sort of a backwards-looking explanation for a consensus standard series like 60601, but I think this explanation hangs together.

 

[yodon]

How to explain the number for probability while the third party auditor asks me?

Presumably you have a table or such outlining what each probability number (range) represents. Hopefully, your FMEA exercises are conducted using a diversity of perspectives (clinical, engineering, etc.) and historical data if available. Having the team concur on a rating gives some assurance that the team has done due diligence in considering the probability.

You need to circle back over the life of the product to assess whether your scoring is accurate based on testing, complaints, adverse events, vigilance, etc.

Side note (1): if you can't come to an agreement, take the higher number.

Side note (2): if you're completely unsure what it should be, you can use the highest number anyway to start <-- this is pretty much straight out of the standard and should be covered in your Risk Management procedure! For software, you have to presume the pre-controls score is the highest probability (100%) and that ensures the severity drives the risk management.

 

[d_addams]

Thank you for the time.

You just mentioned that the P1 value can be different for same Hazardous situation based on the "DIFFERENT FAILURE CAUSES".

Can you just confirmed you said different causes and not the failure modes?

But isn't the P1 value independent?

the failure causes can be synonymous with failure modes.
In your case of compromised graft integrity there can be different causes/failure modes.
Compromised graft integrity due to mechanical overstress
Compromised graft integrity due to fatigue
Compromised graft integrity due to creep
Compromised graft integrity due to stress relaxation
Compromised graft integrity due to corrosion
Compromised graft integrity due to bioinstability.

The 1st four could be captured as a single line item of 'compromised graft integrity due to mechanical forces'

Each of these could have a different P1. Typically one doesn't need to list all possible (in the context of 'anything is possible') failure modes since it doesn't do much good to include a dozen 1:million causes when the most likely one is 1:1000. This is where the 'art' making your risk documents useful vs. pedantically 'complete' comes into play. An example would be including 'due to cosmic radiation damage' as a potential failure cause for every potential hazardous situation.

 

[Bev D]

Hmm. From a ‘classical’ definition of failure mode the term describes essentially adjectives of of the failure. Some have described it as how the failure presents itself. (I’m not particularly fond of this but…)

Failure modes:
Complete failure
Partial failure
Intermittent failure
Unexpected failure

Not mutually exclusive

Others have used the definition you used conflating the terms immediate cause with failure mode

It bears asking for clarity of what definition the OP uses.