Software Standards Compliance 101: Matching system target failure rates to development rigor

Editor’s Note: After a series of fatal accidents, a formal investigation resulted in a recommendations on how to create safety-critical software solutions using a phased approach (see “About this series” at the end of this article). The first phase, Perform a system safety or security assessment, was discussed in “Software Standards Compliance 101: First assess your system’s risk,” the first article in this series. This article discusses Phase 2, Determine a target system failure rate, and Phase 3, Use the system target failure rate to determine the appropriate level of development rigor, with particular attention on how the IEC 62304 standard for Medical device software – Software life cycle processes approaches these objectives. Subsequent articles in this nine-piece series will address the other phases.

In 2014, the FDA released a Medical Device Report that analyzed medical device recalls between 2003 and 2012. This report revealed that recalls increased by 97% during this period, naming device software design as a leading cause. To counter this trend, the International Electrotechnical Commission (IEC) introduced the IEC 62304 standard Medical device software – Software life cycle processes In 2006. This standard codified the current state of practice in developing software for medical devices. In doing so, IEC 62304 established a common framework for medical device software life cycle processes that today is necessary for the safe design and maintenance of such applications.

Rather than being an all-encompassing standard, IEC 62304 works in harmony with other international standards. In particular, it is assumed that medical device software is developed and maintained within a quality management system and a risk management system, the latter of which is specifically addressed in the standard by reference to ISO 14971; Medical devices — Application of risk management to medical devices.

Using Risk to Define Medical Device Classification

Like many of the industry standards that impact the development of software for safety-critical systems, the level of rigor applied to the software development of medical devices is driven by a risk assessment. This assessment determines how likely it is that a patient will be exposed to a particular hazard. Consider, for example, a radiotherapy machine. The radiation that these machines generate can be extremely intense, causing severe injury or death if overexposure occurs. The risk that a patient or therapist will be exposed to this hazard is determined by the severity of the potential injury that may be caused by the hazard in combination with the probability that the exposure will occur.

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