Build and validate safety in medical (and other) device software

Chris Hobbs, QNX Software Systems Ltd.

January 22, 2012

Chris Hobbs, QNX Software Systems Ltd.

    Malfunctions in medical devices don’t usually make the headlines the way airplane or train accidents do. For patients, however, medical device failures can have equally tragic consequences.

    Some of the best-known safety-related standards address functional safety—safety that relies on the continued operation of a (software) system to ensure that persons, property and the environment are kept free from unacceptable risk or harm. IEC 61508 (electrical, electronic, programmable), ISO 26262 (automotive), and the CENLEC 5012x series (rail transportation) all deal with functional safety.

    In contrast, IEC 62304, which is becoming the de facto global standard for medical device software life cycle processes, does not address functional safety. Instead, it addresses the “framework of life cycle processes with activities and tasks necessary for the safe design and maintenance of medical device software” and, through ISO 14971, the risk management associated with those processes.²

    Because IEC 62304 doesn’t address functional safety, it doesn’t define numerical values for acceptable failure rates. Conformity to IEC 62304 doesn’t imply a safety integrity level (SIL) as does, for example, conformity to IEC 61508, which is meaningless without one

    Although IEC 62304 sets out the processes required to produce a compliant device, it is not clear how the quality of those processes relates to the quality of the device produced. This article looks at:

•Nondeterministic systems and the limits of testing

•Building safety

•Validation, including testing, design validation, implementation validation, remaining fault estimation

•COTS and SOUP: commercial off-the-shelf software and software of uncertain provenance

To read the article, which first appeared at Medical Electronics Design, click here.

 

About the author

Chris Hobbs is senior developer of safe systems at QNX Software Systems Limited (Ottawa, ON, Canada).

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