Post-fire ship hull structure and material assessment in International Shipping News 20/03/2026 Fire incidents on ships rank among the most frequent accidents, and in recent years, fire incidents have specially increased among container and ro-ro cargo/passenger ships. DNV has supported many cases of post-fire structural and material assessments, and this news aims to share our insights from this work. What we have observed DNV has supported ship managers, salvage companies, flag states, shipyards and port authorities by providing expertise and in-depth knowledge on the post-fire structural and material assessment of ships. The incidents have ranged from isolated small-scale fires in cargo holds to major fires damaging the complete ship. The fire incidents have identified the need for prompt decision-making in situations where time pressure is high and the crew, cargo and environment are at stake. The situations have involved discussions on whether the ship can continue trading, on the extent of steel renewal and repair methods, on a critical reserve strength assessment while the vessel has been on route, and on fire developing rapidly, fuelled by the cargo (see pictures 1 and 2 below). Damage risks from prolonged exposure Prolonged exposure to high temperatures may result in soft annealing, leading to a reduction in mechanical properties, in particular tensile strength where the steel becomes softer. Another effect is the material hardening, a risk that may occur under uncontrolled quenching during firefighting with seawater or CO2. This could primarily affect the material’s ductility by reducing its fracture toughness and therefore increasing the risk of brittle behaviour. In addition to adverse effects in material mechanical properties, prolonged exposure to thermal loads could result in steel distortions/deformations. The longer the period of heat exposure and heat intensity, the higher the risk that the material properties affecting strength and toughness have been affected. Typically, fire exposure over four to five hours would increase the risk of material and strength deterioration. When post-fire examination reveals permanent waving deformations, this is an indication of long exposure to heat, and material degradation is very probable. If temperatures have not risen over 250–300oC, there is low risk that material would be affected. The extent and magnitude of these deformations would dictate largely the need for repairs. Steel hardening due to cooling under firefighting Steel exposed to high temperatures and cooled down rapidly and uncontrollably, due to firefighting water or CO2 release, increases the risk of hardening and of brittle behaviour, especially if occurred in repeated cycles. This is of particular importance in higher grade steels, which may exhibit lower than original post-fire toughness properties. A conservative approach in emergency situations would be to degrade the material strength by one grade, for example from AH36 (high strength) to NS (normal strength). Hardness testing For post-fire strength and repair plan evaluations, as a minimum, hardness testing of the affected steel according to ASTM A370 is required. Both heat- and non-heat-affected materials should be measured to establish a level of confidence in the measurements. When deemed necessary, destructive testing of samples shall be done under the guidance of DNV (tensile and bend tests as a minimum and location sampling). Structural repairs Structural