Near Loss of Emergency Power

The vessel went aground and damaged the hull, which resulted in water ingress. Partial flooding of the engine room caused shut down of the main generators and as a consequence the emergency generator started automatically. After about 45 minutes it was noted that the emergency generator engine was overheating, leading to a risk of emergency power supply failure.

The emergency generator room was fitted with flaps over the air intake (for engine ventilation and as fire flaps). These vent flaps are normally kept closed and held so by a mechanical spring. When the emergency generator is running, the vent flaps are pushed into an open position by a pneumatic actuator. The actuator is supplied by compressed air from a small accumulator, which in turn is kept pressurised by a connection to the ship’s working air supply.

When the main generators stopped, so did the working air compressor. As a consequence, a possible leak in the ship’s working air system, caused the pressure in the accumulator to drop, thereby closing the vent flaps, which led to air starvation, insufficient cooling air and subsequent overheating of the emergency generator engine. In this case, the resulting smoke emission from the emergency generator room was detected by the crew who managed to force the vent flaps open and restore the emergency power supply.

Subsequent investigation revealed that the original pneumatic “self-contained system”, could have been designed differently. That is, with a non-return valve, to prevent loss of pressure in the accumulator, thus maintaining sufficient air pressure to hold the air vent flaps open.

The mentioned incident teaches us the following:

During an emergency situation, the crew should carry out regular checks of the emergency generator room to ensure safe operation in general, and as illustrated in this case, that unobstructed air supply is maintained.
If the emergency generator room is equipped with remotely controlled air vent flaps, the crew should periodically make sure the mechanism which controls the flaps is working properly.
The revised ISM Code (amended 1 July 2010), highlights even more than before, to assess risks, e.g. “assess all identified risks to its ships” and “identify equipment and technical systems the sudden operational failure of which may result in hazardous situations”. The illustrated case is one small, but vital, example of technical systems, which may be identified in such processes. Identifying risks is a continual process and the crew and management should regularly ask the question “What if …?” for the most unlikely situations.