Engine Room Fire on Mobile Offshore Unit

A fire occurred in the port engine room of a semi-submersible drilling unit whilst carrying out exploration drilling in Norwegian waters. The fire was indicated by alarms in the control room and confirmed by attending personnel. The engine room was successfully isolated manually after approximately 35 minutes, and the halon system was then activated. This, however, did not completely extinguish the fire, which re-ignited. The fire was eventually extinguished some 7 hours after the initial alarm.

Whilst the unit was on fire, the crew had to contend with a total electrical blackout, loss of firewater, loss of remote control of the ballast system and the unanticipated activation of the anchor line payout system which necessitated well disconnection.

The engine room suffered substantial heat and water damage to cabling, hydraulic systems, diesel generators and switch gear. In addition, three anchors were lost due to uncontrolled payout of the anchor lines, and the drill string was cut as a result of the emergency well disconnection.

The investigation into the incident concluded that the fire was probably the result of a leaking pressure gauge needle valve in the fuel oil supply to the diesel generators in the engine room, which sprayed diesel fuel onto hot components of the engines. The shielding of hot surfaces does not appear to have functioned properly.

The preprogramming of the power management system resulted in stoppage of the fire pumps as well as preventing their restart, in spite of power being available. The cables running from the winch control unit to the anchor winches were routed through the engine rooms.

The fire in the port engine room short circuited these cables and the forward port side anchor winches began paying out only 13 minutes after the fire was detected.

The cable running from one of the ESD (Emergency Shut Down) activation panels to the ESD master control panel in the control room was also routed through the engine room affected by the fire. Although fire resistant, the cables became hygroscopical after the insulation material burnt through. The cable was exposed to water from the firefighting and subsequently short circuited. ESD level 2 was activated, causing the shutdown of both the emergency and the main generators in the starboard engine room. The result was total loss of power.

Due to loss of position it was necessary to shear the drillstring and close the blow-off preventer (BOP). The cable from the battery source to the BOP activation panel was routed outside the fire area, but the batteries were linked to the ESD system and were probably shut down due to the shortcircuited ESD system.

The hydraulic pipes from the ballast control panel to the hydraulically-operated ballast valves in one pontoon were routed through the burning engine room. The pipes were damaged and the hydraulic oil tank emptied, so that neither of the pontoons’ ballast systems could be operated from the control room.

Lessons to be Learned from the aobve incident include:

The unit was equipped with two engine rooms, either of which could act as an emergency generator room (see Figure 1). Routing of cabling to critical systems through both engine rooms made the unit vulnerable in the event of an engine room fire. Ships with similar engine room arrangements could be similarly at risk.
The design of the ESD system and the anchor release system was not fail-safe, and resulted in unintended activation after the cable short-circuited. Fire-resistant cables may become hygroscopical in fires. Generally, cables supplying essential or important consumers should not be routed through fire risk areas such as engine rooms.
The hydraulic power system on board supplies several consumers. Each consumer should have a separation valve on the supply line to prevent leakage in one system making other systems inoperable.
Control room operators must be familiar with all integrated/ programmed systems on board which carry out automated actions during an emergency situation. This can only be achieved through regular scenario-based training.
Personnel on board must be familiar with the fire extinguishing properties of Halon and the relative toxicity of its various types, so as to avoid misunderstandings and delays when a fire is detected and to ensure a quick and correct response in an emergency situation.