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A collision between two cargo ships near Port Arthur, Texas last year was caused by a loss of propulsion resulting from a false alarm, the National Transportation Safety Board (NTSB) announced on Thursday.
On August 21, 2022, while transiting Sabine Pass, the Netherlands-flagged cargo ship Damgracht lost propulsion after the vessel’s main engine shut down due to a “high oil mist density” detected by its oil mist detector (OMD). The abrupt loss of propulsion caused the vessel to veer into the path of another bulk cargo ship, the Croatian-flagged AP Revelin. Despite efforts by the pilot aboard the Damgracht to notify AP Revelin and avoid the collision, the two vessels collided.
Although no injuries were reported, the collision caused $3.4 million in damages to the AP Revelin.
The NTSB’s investigation revealed that the day before the collision, the main engine of the Damgracht alarmed and later shut down due to a high cooling water temperature. The engine crew cooled down the main engine that evening and repaired a failed cylinder head gasket. The NTSB said the gasket failure likely allowed cooling water to leak into the cylinder, contaminating the engine’s lube oil system, and exposing the engine’s interior sections to humid conditions.
According to the NTSB, humidity averaged about 90% that evening, which could have caused higher levels of water to enter the crankcase than could be removed overnight by the lube oil purifier or evaporate from the heat of the running engine during the short time it was tested post-repair. While the Damgracht was underway the following morning, the OMD triggered a false alarm after sensing water vapor that had condensed in the sample.
The NTSB determined the probable cause of the collision was the Damgracht’s loss of propulsion caused by an automatic shutdown of the main engine due to the false alarm, likely triggered by water vapor sensed by the oil mist detector shortly after engine maintenance was completed to replace a failed cylinder head gasket during high-humidity conditions.
According to the report, “When certain engine components, such as cylinder head gaskets, fail, cooling water can be introduced into engine lube oil systems. Ambient air conditions, such as high humidity or extreme cold temperatures, can also increase the water content within engine lube oil sumps. The elevated quantity of water in lube oil systems can trigger false alarms in engine crankcase oil mist detectors (and lead to an engine shutdown), due to water droplets passing through the measuring track or the filter glass detecting condensation (mistaking it for oil mist). After an engine’s crankcase is opened and exposed to these conditions during maintenance and repair, it is good practice for engine crews to inspect and test the lubricating oil system for water intrusion and ensure lube oil purifying equipment is functioning properly to remove any water or other contamination in the lube oil.”
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