PEM Stack Thermal Runaway Prevention Protocol (UL 6251 Annex F)

Thermal runaway in PEM electrolyzers arises when localized heat generation (e.g., from high-current density operation, membrane drying, or oxygen/hydrogen crossover) exceeds dissipation capacity, triggering accelerated electrochemical side reactions, membrane decomposition, and potential fire or explosion. UL 6251 Annex F addresses this by prescribing a layered defense-in-depth strategy: first, continuous spatially resolved temperature monitoring (≤2 °C resolution, ≤1 s sampling) across stack manifolds and end plates; second, mandatory dual-channel, independent thermal cut-off logic with hardwired emergency shunt bypass and rapid anode/cathode pressure venting; third, design validation via worst-case fault injection testing (e.g., simulated single-cell short, coolant flow loss, or sensor failure). The protocol further requires thermal modeling verification — including transient 3D CFD simulations under fault conditions — and mandates that all safety-critical functions remain operational even after single-point hardware faults (per SIL-2 equivalence per IEC 61508). Implementation extends beyond hardware to include firmware-level watchdog timers, secure boot integrity checks for thermal control algorithms, and traceable calibration records for all temperature and pressure sensors used in the safety chain.