On October X, 2026, FS Micro Laboratory※1, a research laboratory specializing in ISO 26262※2, announced that a paper by its principal researcher, Atsushi Sakurai, has been accepted for the 73rd Annual Reliability and Maintainability Symposium (RAMS 2027)※3, an international conference sponsored by the IEEE※4 Reliability Society.
This marks the eighth consecutive year, since 2020, that Sakurai's papers have been accepted at RAMS. The paper will be presented at RAMS 2027, to be held in Florida, USA, in January 2027.
Sakurai's contributions to ISO 26262 began with a paper accepted at an IEEE international conference in 2017, which received the Best Paper Award, and have continued with a more accurate PMHF※5 formula proposed at RAMS 2020, among other work.
The new paper analyzes the origin of a PMHF formula frequently found in the literature, expressed as a simple sum of failure rates, and identifies its source in the PFH※7 formula of IEC 61508※6. The paper then rigorously derives PMHF and PFH on a common mathematical model, and shows that the resulting expressions contain a term that the simple sum of failure rates does not.
This result means that the simple-sum PMHF formula overestimates safety and can even reverse a compliance decision against a safety integrity target. The paper further shows that the PFH formula of IEC 61508 is exact in its simple-sum form only under an idealized condition: perfect and continuous proof testing. This condition is rarely met in practice, in the automotive domain or elsewhere.
These results support a clearer understanding and proper application of both metrics, especially PMHF, in automotive safety analysis.
【Notes】
※1：FS Micro Laboratory (Nagoya, Japan; Principal Researcher: Atsushi Sakurai): A research laboratory specializing in the functional safety of automotive systems. https://fs-micro.com/
※2：ISO 26262: An international standard for the functional safety of automotive electrical and electronic systems, aimed at reducing the risk of hazardous events during driving to an acceptable level.
※3：RAMS (the Reliability and Maintainability Symposium): An international conference on reliability engineering sponsored by the IEEE Reliability Society and others. The 73rd symposium will be held in Florida, USA, in 2027. https://rams.org/
※4：IEEE (Institute of Electrical and Electronics Engineers): One of the world's largest technical professional organizations dedicated to advancing electrical and electronic technology. https://ieee.org/
※5：PMHF (Probabilistic Metric for Random Hardware Failures): A metric representing the time-averaged probability of dangerous failures caused by random hardware failures, used as a hardware design target in ISO 26262.
※6：IEC 61508: The generic functional safety standard for electrical and electronic systems, on which sector-specific functional safety standards, including ISO 26262, are based.
※7：PFH (average frequency of a dangerous failure per hour): A quantitative metric used in IEC 61508 for safety functions operating in high-demand or continuous mode.
【Contact】
Company FS Micro Laboratory
Representative Atsushi Sakurai
Established August 21, 2013
Business Research on functional safety of automotive electronics under ISO 26262
Email info@fs-micro.com
URL https://fs-micro.com/
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