Where the Protection of a Ship Hydrogen Fuel Cell Room Boundary Actually Resides: Fire-Resistance Rating, Shutdown Speed and Flame Detection

The International Maritime Organization (IMO) circular MSC.1/Circ.1647 requires a ship’s fuel cell space to be bounded by “A-60” divisions and permits equivalent-safety alternatives without defining equivalence. This study proposes a framework that reads boundary rating, fire exposure and shutdown response as interacting protection layers. A full-bore rupture of an in-service vessel’s 10 mm, 0.8 MPa line gives a 4.75 MW source term. The boundary is loaded with prescribed fluxes of 50–250 kW/m2, not a predicted fire field. A one-dimensional wall model, calibrated on one test series and checked against seven independent tests, was run over 60 cases of grade, shutdown time and exposure. At 250 kW/m2, the modelled A-60 column exceeds the 140 and 180 °C rise limits after about 24 and 40 min. Resolved spatially, the local limit is still exceeded. Shutdown speed sets what the boundary contributes: A-30 and A-15 stay within an insulation-only A-60 benchmark if isolation occurs within 102–103 s, against 1.8–5.1 s from component data. This is one building block of an equivalence case, not A-60 or system-level equivalence: integrity, reliability and explosion are not assessed. MSC.1/Circ.1701 calls for detectors suitable for hydrogen fires. Hydrogen-capable detectors exist, but the cited route through the Fire Safety Systems (FSS) Code to EN 54-10 supplies no harmonized hydrogen test fire.