The UK MAIB has reported an incident in which an uncontrolled fire broke out in the furnace of a thermal oil heater onboard a passenger/ro-ro cargo ferrywhile approaching port.
Following an alarm on the ship’s fire detection system, an engine room team proceeded to the port boiler room to investigate. Pulses of smoke were seen to emanate from the jointing surfaces at the top of the port thermal oil heater. The boiler room ventilation was stopped from the bridge and fire-fighting teams were prepared. Meanwhile, the chief engineer gave instructions for the port thermal oil heater to be shut down, the burner fuel and air supplies to be isolated, the thermal oil supply by-pass valve to be opened, and the thermal oil heater coil inlet and outlet valves to be closed.
The chief engineer considered that the fire had probably been caused by a coil failure that had allowed thermal oil to pass into the furnace. He advised the master accordingly, who informed the port authority and requested that the local fire and rescue service meet the ship on arrival. On seeing the burner unit, located at the top of the thermal oil heater, lift and remain open, the chief engineer entered the port boiler room and closed it.
However, owing to the presence of dense smoke he was unable to remain in the compartment long enough to properly secure the burner unit, which re-opened shortly afterwards. Concerned that the thermal oil pressure in the heater coil would rise to an unacceptable level, the chief engineer sent a fire team into the port boiler room to manually operate the heater coil pressure relief valve. But, conditions had worsened within the compartment and the team was unable to complete the task. Shortly afterwards, the dry powder fixed fireextinguishing system for the port thermal oil heater was activated on the chief engineer’s instruction.
The ship was then berthed alongside and firefighters from the local fire and rescue service boarded. Following a discussion between the chief engineer and the shore firefighter in command, it was decided to make an entry of the port boiler room using a combined team of ship’s crew and shore firefighters. The plan was for the ship’s crew to operate the heater coil pressure relief valve and for the shore firefighters to inject dry powder directly into the heater furnace. On opening the port boiler room entrance door, an unexpected fireball swept across the open deck, knocking over and injuring a number of personnel in the vicinity.
The door was then closed, and the hi-fog water fixed fire-extinguishing system for the port thermal oil heater activated, while the ship’s crew started boundary cooling around the port boiler room. The shore firefighters later deployed their own combined water-jet cutting and fog nozzle fire-fighting equipment to assist in cooling the compartment. The fire was finally declared extinguished some 12 hours after it had started.
Lessons Learned
1. The fire started because a fracture had developed in the coil carrying thermal oil through the furnace. This allowed the oil to enter the furnace and ignite. The fracture was situated along a circumferential weld securing the refractory insulation support plate at the top of the furnace, where a number of previous repairs were evident. The section of coil that failed was particularly difficult to inspect visually due to the refractory insulation in the vicinity. There were no detailed maintenance records referring to the previous repairs. Had such records existed, the area could have received more attention during inspections, prompting hydraulic pressure testing where the coil was not accessible for visual external examination.
2. The port boiler room had three separate fixed fire-extinguishing systems:
- A dry powder system designed to extinguish a fire on top of the thermal oil heater.
- A hi-fog water system designed to extinguish a burner unit fire on top of the thermal oil heater.
- A CO2 system designed to provide fireextinguishing capability for the whole compartment.
Dry powder will only remain effective while it is present in the atmosphere above the fuel; it has no cooling effect, resulting in a high risk of rapid reignition. The hi-fog water system wouldhave been a preferred option for use in extinguishing the fire at an early stage. However, heat from the open burner unit aperture disabled its automatic function and, despite a number of indications that the fire had spread into the port boiler room, its manual use was delayed. Instead, the ship’s crew and shore firefighters remained focused on fighting a fire that they considered was contained within the thermal oil heater.
A comprehensive review of all available information, involving all key ship and shore personnel, would have allowed a fire-fighting plan, appropriate to the actual situation, to be developed and agreed. Furthermore, had a standard operating procedure for dealing with a thermal oil heater fire been developed and exercised as part of the training programme on board, the ship’s crew would have been better prepared to deal with the emergency.
3. Limited ventilation can lead to a fire in a compartment producing gases containing partial combustion and unburnt pyrolysis products. If these accumulate, an admission of air when an opening is made to the compartment can cause a backdraught, resulting in a fireball moving through the compartment and out of the opening.
A thorough situational risk assessment would have allowed the risk of backdraught conditions within the port boiler room to be identified and a revised entry plan to be developed and agreed.
Source: UK MAIB Safety Digest 2/2016
