Transport Malta has released a simplified final report into a starting air explosion during berthing operations aboard CMA CGM Shanghai in Singapore.
What happened
CMA CGM Shanghai arrived just outside its designated discharge port of Singapore in the early hours of 15 March 2025, completing an 11-day voyage from Karachi, Pakistan.
The vessel was expected to remain outside port limits for approximately 50 minutes. During this time, the crew prepared the pilot ladder and completed arrangements for the pilot, who boarded the vessel at 0612 local time.
At around 0700, the crew was called to standby once more in preparation for berthing and mooring. Tugs were secured at the forward and aft ends, and at 0742, the pilot ordered ‘dead slow ahead’ on the main engine. The chief mate moved to the port wing telegraph to execute the order.
At that moment, a loud explosion was heard from the aft section of accommodation block.
Smoke was seen emanating from the area, and multiple alarms, including the fire detection system, sounded on the bridge. The water mist system inside the engine-room also activated.
Although the engine telegraph was returned to the stop position, the pressure gauges showed a loss of control air pressure. The chief engineer, who was in the engine control room at the time, reported significant technical issues with the main engine to the bridge, but confirmed that no fire was present in the engine-room.
Following a discussion with the pilot, the master requested two other tugboats to assist the vessel during berthing.
The vessel came safely alongside at about 1049. A preliminary inspection by the chief engineer revealed that an explosion inside part of the main engine starting air pipe had occurred.
Reported injuries and extent of damage
No injuries were reported to any of the crew members.
Three starting air valves were found with damaged compressed springs. The inlet pipe to the main starting air valve had exploded, including various 90° bends, suggesting localised overpressure or stress concentration. The main starting air valve itself sustained damages, and the end flange of the main starting airline was blown off due to the force of the blast.
Additionally, all the burst discs installed in the system had ruptured. Other areas in the engine-room were also affected, either by the flying debris or the explosion per se.
Probable cause
The probable cause of the starting air explosion was one of the starting air valves on the cylinder head, which remained (partially) open.
A sticking starting air valve during manoeuvring is a possible cause of an explosion in high-pressure starting air pipelines. Records of the starting air history made available to the safety investigation indicated that there were three main engine starts and the explosion happened during the third and final start. In fact, the records indicted two drops in the air start pressures (coinciding with two starts), and a final pressure drop, which was never recovered.
For an explosion to happen, one of two possible processes had to happen. Both processes would have generated very high velocities and shockwaves, which may also rupture pipes and fittings.
The first process is through the ignition of a mist of lubricating oil. Under normal operating conditions, some lubricating oil mist is discharged from the air compressor to the air start system. However, this may be exacerbated with excess compressor cylinder lubricating oil, faulty oil scrapper rings and oil vapour suspended in the engine-room, which may be drawn in the compressor suction side.
Small quantities of lubricating oil will deposit as a thin film, over the internal pipe surfaces. With a sticking air start valve, unburnt fuel and cylinder lubricating oil will be blown through the valve to the adjacent air manifold. Further heating from the sticking valve will cause the deposited oil film to carbonise and form incandescent carbon.
When starting air is applied to the system whilst still hot, the high-pressure air coming in contact with the burning carbon may cause an explosion inside the pipe. The explosion will cause a flame to pass back through the air start system, evaporating the deposited oil film and igniting it, in the presence of air.
It is pertinent to highlight that if excessive lubricating oil enters the air start system, it would be possible for a mixture of air and oil droplets to be discharged through the open starting air valve. This spray may ignite due to high temperatures in the cylinder, causing a flame to pass back through the (still) open air start valve to the air manifold.
Keeping oil discharge from the compressor to a minimum will also reduce the possibility of oil carry over into the starting air system. Moreover, starting air receivers must be drained regularly during the watch. Drains are a SOLAS requirement and are fitted to minimise the oil ingress into the starting air system.
While this process was considered during the safety investigation, multiple factors suggested that it did not fully explain the occurrence.
For instance, the system was fitted with automatic drain valves and therefore, drainage of the system was not an issue. Moreover, after the explosion, the air compressors were overhauled, and the piston rings’ gap clearances were measured at specific heights, as per manufacturers’ instructions.
All measurements confirmed that the material wear was within the permissible tolerances. The records also indicated that although the lubricating oil consumption was highest for starting air compressor no. 4, it still fell within the normal range and, as for the other compressors, no action was required in that respect.
The second process potentially involved combustion gases, possibly containing unburnt fuel, oil mist, and soot, to enter the air start system. This would have typically occurred during the power stroke, when high-pressure gases from the combustion chamber are forced backward through the partially open air start valve into the air start manifold.
The presence of fuel or fuel vapours in the compressed air system would have created a highly dangerous condition, as the air start manifold would be filled with high-pressure air. This mixture is highly explosive and could have posed a significant risk of backfire or detonation.
A single hot spot or spark could trigger an explosion within the manifold, which can rupture nearby starting air valves and lead to a series of mechanical failures.
Download the full report: Transport Malta investigation report 04-2026-MV-CMA-CGM-Shanghai