*Note:
This monthly safety moment is collected from various sources for
educational purpose and is not an
actual incident from the ESM fleet. |
| Lagging Fire in Pump room of a Chemical Tanker |
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|  A fire occurred in the pump room of a chemical tanker while it was loading a hot bitumen cargo at a refinery. The chemical tanker was on a long term charter to transport bitumen cargoes, and was designed for this trade.
On this occasion, the cargo was of a specialist variety for heavy industrial use, and its transport temperature of 220°C was much hotter than that of standard bitumen cargoes which are normally carried at 150°C. To prevent the bitumen from cooling and hardening in the cargo pipelines and the cargo tanks, a thermal oil trace heating and tank heating system was in operation at about 225°C. The piping system was covered by thick pipe insulation.
The bitumen was loaded into the cargo tanks via the pump room and, as an added precaution because of the higher temperatures involved, the pump room fire flaps and access door had been shut. This measure had been taken as part of the vessel’s informal risk assessment for this cargo. Four and a half hours after loading had begun, smoke was noticed coming from the pump room extraction fan. The pump room fire and gas detection alarms sounded very soon afterwards.
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The chief engineer made his way to the pump room. He donned self-contained breathing apparatus (SCBA) and entered the space alone. He was met by thick black smoke which prevented him from proceeding beyond the top level. He retreated and returned to the bridge, where he 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.
The fire brigade were informed of the relevant facts. After entering the seat of the fire was located at the lower level of the pump room using thermal imaging equipment. It was quickly extinguished with water hoses. Within a short time, the pump room was ventilated. On investigation it was found that the seat of the fire had been the lagging of a cargo discharge pipe, which, although empty of bitumen, was being kept warm by the trace heating lines. Above the cargo discharge pipe a hydraulic hose was found to be leaking from an end fitting. It is thought likely that hydraulic oil had dripped onto, and subsequently soaked into, the lagging. Spontaneous ignition had eventually occurred. Fire damage was limited to the lagging, and smoke damage confined to the pump room. |
LESSONS
LEARNT
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Spontaneous ignition can occur in oil soaked lagging at liquid temperatures as low as 130°C. This can be considerably lower than the oil’s auto-ignition temperature, due to the fluid’s oxidisation. This phenomenon is well known and commonly labelled a “lagging fire”.A number of factors are involved in determining the likelihood of a lagging fire: thickness and type of insulation, type of oil, rate of leakage, oil temperature and air flow can all alter the balance between heat loss and heat generation. Of particular note is the fact that the liquid does not need a low flash point, and non-fuel oils such as thermal and hydraulic oils are more likely to generate a lagging fire.
Good housekeeping and maintenance, including the prevention of leaks, cleanliness and the provision and regular inspection of sealed lagging are the simplest measures that can be taken to prevent lagging fires.
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In his haste to determine the extent and cause of the fire, the chief engineer entered a smoke-filled space alone, wearing SCBA. This is poor practice, and with the visibility almost nonexistent, he could easily have fallen or lost orientation and thus added a casualty to further complicate the situation.
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