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100% probability of software failure in IEC 62304 Amd1 2015

A reader of the post on IEC 62304 Amd1 2015 noticed in the comments that the sentence in section 4.3.a was removed:

If the HAZARD could arise from a failure of the SOFTWARE SYSTEM to behave as specified, the probability of such failure shall be assumed to be 100 percent.

Don't be too quick to scratch the 100 percent thing!

The dreadful 100 percent is still present in the informative Annex B.4.3.

Even if it is no more in the normative part, you shall continue to bear in mind this assumption when assessing software risks. The underlying concept is that it's not possible to assess probability of software failure, thus the worst case shall be considered.
This is the state-of-the-art, present in ISO 14971, in IEC 80002-1, in IEC 62304, and in the FDA Guidance for the Content of Premarket Submissions for Software Contained in Medical Devices.

100% probability is not dead!

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