Hong Kong Merchant Shipping Information Note
After the maintenance of the furnace of a thermal oil heater on board a Hong Kong registeredvessel, the furnace exploded during test run. The explosion caused serious injuries to threecrewmembers and damage to the thermal oil heater cover and its surrounding equipment andfittings. The Hong Kong Marine Department has issued Information Note to draw the attention of the shipowners, ship managers, shipoperators, masters, officers and crews, manufacturers and classification societies to the lessonslearnt in the accident.
The Incident
The accident happened on board a Hong Kong registered oil tanker when it wasanchored at Moreton Bay outside Brisbane River.2. Before the explosion, the No. 2 thermal oil heater on board the vessel failed to fire on anumber of occasions. The engineers then worked on the burner unit to rectify the problem. Theaccident occurred when the engineers tried to fire the furnace after completed the maintenance ofthe burner unit. During the trial, fuel oil was circulating through the heater and the temperatureof the furnace was around 160C. The fuel in use was marine gas oil of flash point 68C. Theexplosion occurred when the engineers started to fire up the furnace.
Investigation after the accident found that the burner nozzle was incorrectly assembledwith a deformed needle valve stem. The supply of gas oil could not be sealed by the needlevalve stem and fuel oil leaked from the tip of the burner into the furnace of the heater during thepre-ignition cycle.
For the thermal oil heater on board, the manufacturer recommended that if heavy fueloil (HFO) was used, the pre-ignition cycle time should include time for fuel oil heating plus sixtyseconds for pre-ignition purging. The total pre-ignition cycle time set on board the vessel wasfour minutes when using HFO for the heater. Before the explosion, the fuel supply to theburner unit had been changed to MGO which required no heating. However, the pre-ignitioncycle time had not been reduced to one minute accordingly as recommended by the manufacturer.Fuel oil leaking from the incorrectly assemble burner unit during the pre-ignition cycle vaporizedunder high temperature inside the furnace. As a result, a large volume of combustible gasesaccumulated inside the furnace prior to the ignition. When ignition started, the combustiblegases inside the heater exploded causing the accident.
The investigation into the accident conducted by the Australian Transport SafetyBureau also revealed that:
a) The swirl plate was not properly installed in the burner nozzle thus causing theneedle valve not rested on its seat which resulted in fuel leakage after the burnerunit was installed on the oil heater;
b) The instruction manual of the thermal oil heater did not provided sufficientinformation for the maintenance of the burners.6. It was also found that the engineers on board had no training and had little experiencefor the maintenance of the burners. There was no equipment on board to test the function of theburner after maintenance.
Lessons Learnt
For the maintenance of machinery components, they must be assembled correctlyaccording to the manufacturer’s instructions and manual. If the instructions are not very clear,the functions and correlation of each component must be clearly understood before assemblingthem together. Tests must be carried out under such circumstances to ensure that the unitfunctions properly after assembly.
The attention of shipowners, Ship Managers, Ship Operators, Masters, Officers andCrews, Manufacturers and Classification Societies is drawn to the lessons learnt above.