LAGGING FIRES - HIDDEN DANGER The lagging fire phenomenon occurred while a small chemical tanker was loading a hot bitumen cargo at a refinery. NARRATIVE A chemical tanker was transporting hot bitumen, and was designed for this trade. The cargo was of a specialist variety, and its transport temperature of 220øC was much hotter than that of standard bitumen cargoes normally carried at 150øC. To prevent the bitumen from cooling and hardening, a thermal oil trace heating and tank heating system was in operation at about 225øC. The piping system was covered by thick pipe insulation. The bitumen was loaded into the cargo tanks via the pump room and the fire flaps and access door had been shut as an added precaution. Four and a half hours after loading had begun, the chief engineer and chief officer noticed smoke coming from the pump room extraction fan. The fire and gas detection alarms sounded. The chief engineer went to the pump room. He donned self-contained breathing apparatus and entered. Thick black smoke prevented him from proceeding beyond the top level. He returned to the bridge and informed the master of the situation. The refinery was contacted and emergency procedures were implemented. The loading was stopped and the local fire brigade arrived on scene within a few minutes. They were informed of the relevant facts, including the type of cargo being loaded, and entered along with the chief engineer. The seat of the fire was located at the lower level via thermal imaging. It was extinguished with water hoses. The pump room was then ventilated. The seat of the fire was the lagging of a cargo discharge pipe, which, although empty of bitumen, was warmed by trace heating lines. Above the cargo discharge pipe a hydraulic hose was leaking from an end fitting. It is likely that hydraulic oil had dripped onto, and subsequently soaked into, the lagging. Spontaneous ignition eventually occurred. LESSONS - The vessel had a fixed CO2 fire-fighting system, but it was not made ready for instant use should the fire have got out of control or proved more serious than at first thought. - The use of water to bring the fire under control was effective in this case but, taking into account the type of cargo and the unknown nature of the fire, it was risky. Source: UK MAIB
Posted on: Mon, 06 Oct 2014 08:14:43 +0000
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