M1794 - Fire in LNG carrier compressor room?

Initial Report

The Dual Fuel Diesel Electric (DFDE) LNG carrier was on passage at sea at night. At around 0400, the reporter was woken by a fire alarm and a PA announcement that there was a fire in the compressor room, which is an unmanned space (UMS). Fearing an explosion, the reporter donned PPE and met the senior engineer outside the compressor room. It took both of them to open the door against the positive air pressure in the compartment. From the doorway, they could see no sign of fire or smoke but did not enter immediately because neither had remembered to collect portable gas detectors. They sent for them, and once these had arrived and they confirmed that there was no gas present, the three-person fire team entered the compartment wearing breathing apparatus. A thorough search confirmed that there was no fire.

The bridge team were convinced that they had seen flames coming out of the compressor room. The three person team checked the adjacent motor room and confirmed no fire. The emergency party went to the bridge, and the bridge team told them that they had seen a big cloud coming from the compressor room ventilation shaft. This was inspected and found warm, so the team concluded that the bridge team had mistaken a steam cloud for flames and smoke in the darkness.

Further investigation revealed that there had been a loss of electrical power throughout the ship, which had been restored only a few moments before the fire alarm sounded. The ship continued sailing, but it was discovered that the fire detection panel was faulty, and the gas detection mode switched off, so there was no way to identify a fire or gas leak.

CHIRP Comment

LNG carriers use an inert nitrogen gas system in the motor room and compressor room to keep out air/oxygen and water vapour, which could freeze and damage critical equipment. It also serves to reduce the risk of fire. Excess nitrogen gas is vented through a small gooseneck vent on the compressor room roof, which can be seen from the bridge. Usually, the quantity released is
very small and almost unnoticeable, but in a power failure, the system will expel a greater amount in a sudden burst. The gas is super-cooled, and when it meets the atmosphere over the compressor room roof, it causes water vapour to condense into a steam cloud which can look like smoke.

The vessel had suffered a loss of electrical power because the uninterruptable power supply (UPS) had not worked. The loss of power triggered the fire alarm, further reinforcing the perception of a fire in the compressor room. Because the vessel was newly built (around a year old) and had only recently entered service, the UPS defect likely existed since she was built but had not been previously detected. A review of the existing UPS test and inspection regime would be beneficial, as would raising the bridge team’s awareness of the effects of a loss of power on the nitrogen gas system and the likelihood that a temporary burst of steam may be seen shortly afterwards.

Situational Awareness – People awakened from deep sleep can feel groggy and disoriented for several minutes after they wake up. This hampers our ability to build situational awareness and explains why the portable gas detectors were not collected initially. Written aide memoir lists can sometimes be beneficial in such circumstances.

Alerting – The bridge team was right to raise the alarm because they believed there was a fire in the compressor room.

Teamwork – The report did not mention that a headcount of everyone on board had taken place, but this is good practice in an emergency.

Training – Responding to an emergency at night is more challenging than during the day. Do you conduct emergency drills at night?