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.
And DNV has supported many cases of post-fire structural and material assessments.
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.
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.
Need to know
- Fire exposure can degrade steel strength and toughness, increasing the risk of brittle behaviour or loss of strength.
- An accurate post fire assessment requires hardness testing (ASTM A370) and, when needed, destructive testing, to determine whether steel grade downgrading or structural repairs are necessary.
- DNV provides rapid emergency and post fire support, including strength assessments and drone-based surveys for quick, safe evaluations.
Find out more: DNV – Post-fire ship hull structure and material assessment