EMC & Transient Safety

It is the treatment of the electrical environment as a fault source inside the functional safety argument. Electromagnetic interference, electrostatic discharge, load dump and coupled transients can corrupt signals, upset logic and disturb supplies, producing faults in perfectly healthy hardware. These events do not appear in the random-hardware-failure math - they are not component failures with FIT rates - so ISO 26262 handles them through environmental robustness requirements, dependent failure analysis and the safety concept: immunity levels derived from safety goals, hardware defenses such as filtering and shielding, and software measures such as plausibility checks that keep disturbances from becoming safety goal violations.

Because CISPR 25 is an emissions standard: it protects radio reception on the vehicle from your electronics. It says nothing about immunity - the ability of your system to keep functioning when disturbed. Passing it makes your ECU a polite neighbor, not a robust one. The same trap applies to the UN R10 E-mark, which applies generic reference levels rather than hazard-derived requirements, and to AEC-Q qualification, whose ESD content addresses assembly-line handling, not operational discharge. Chapter 13 works through these fallacies explicitly.

Through a coupling path and a susceptible circuit. Energy couples conductively through the harness and supply, capacitively or inductively between adjacent conductors, or as radiated fields onto cable and board structures. Once inside, it can shift analog levels so conversions read wrong, glitch clocks and resets, upset logic states, or corrupt communication bits. The result looks like a random fault - a wrong sensor value, a hung peripheral - but with a crucial difference: it can hit redundant channels simultaneously, which is why EMC is a classic common-cause concern.

You start from the hazard and work backwards. For each safety goal, identify the functions whose disturbance could violate it and the time window - the FTTI - within which a disturbance-induced fault must be detected or ridden out. Then set immunity levels and functional status classes for those functions above the homologation floor, choosing test levels and monitoring that demonstrate the function either stays correct or degrades safely during the disturbance. Chapter 9 builds this argument structure, and Chapter 12 shows how to verify it by monitoring the safety function during EMC testing.

It includes 13 chapters: the hostile electrical environment, the disturbance zoo, the physics of disturbance-to-fault coupling, the ISO 26262 lens, a standards map covering ISO 7637, ISO 11452, ISO 10605, ISO 16750 and CISPR 25, deep dives on supply transients and load dump, ESD, and radiated immunity, then immunity as a safety argument, hardware defenses, software and system defenses, verification, and a closing chapter on pitfalls and the safety case that debunks the common compliance fallacies.