UK MAIB informed of a pressure accident onboard a multicat vessel. Operators carried out an unrecorded modification to the supply fan flap support brackets, without consulting the shipbuilder, which led two crew members to be sucked into the engine room with severe force. MAIB advised that any modifications need to consider all aspects of the application being altered.
The incident
A multi-cat vessel was transiting between two Scottish ports when the engine room supply fan flaps closed. The exhaust fan flaps remained open and the engine continued to draw combustion air from within the machinery space. As a result, a vacuum formed in the compartment.
The vessel had been supplied from the builder with the ventilation fan flap support brackets in different orientations on the exhaust and supply systems. The brackets were designed to allow the flaps to be closed quickly in the event of an engine room fire to isolate the compartment.
An unrecorded modification to the supply fan flap support brackets had been carried out by the vessel operators to align all the brackets in the same orientation. This had been completed without consulting the ship builder.
The vessel was relocating from one port to another in preparation for a new contract. The weather conditions were not the most desirable but within the vessel’s operating limits. As a result of the sea conditions the vessel was rolling and pitching. The vessel’s motion resulted in the supply fan flap arms dropping out of their support brackets, which allowed the flaps to close. The subsequent vacuum within the engine room ensured that the flaps remained tightly closed.
The vessel was operating with an unmanned engine room. As the available air in the compartment was consumed, the engine efficiency dropped, resulting in rising exhaust temperatures and a consequent increase in the compartment’s ambient temperature. The rising temperatures activated a high exhaust temperature alarm on the engine and a high compartment temperature alarm for the engine room.
With both alarms sounding, the master sounded the general alarm and mustered the crew. The master and the offshore manager identified the problem and discussed potential solutions. These included lifting the main deck access hatch to the engine room, attempting to open the supply fan flaps, or opening the main access door to the engine room located within the vessel’s stores area.
Opening the engine room hatch or supply fan flaps was ruled out as the weather was now making access to the outer decks too dangerous. Therefore, it was decided to open the internal engine room door. The master and the manager evaluate that the pressure differential would be reasonably low and that three people could adequately control the inward opening door. On arrival at the door it was apparent that available space would only allow two people to control the opening.
Nevertheless they decided to proceed. As the door latching mechanism was released, the door opened violently inwards and the two crew members were sucked into the engine room, both striking structure and machinery as they were dragged in. Both of the crewmen remained conscious and were able to exit the engine room unaided.
The engine and compartment temperature returned to normal operating parameters and the vessel proceeded into port, where the casualties were evacuated for medical assessment and treatment.
- Some of the ventilation fan flap support brackets were incorrectly orientated when the vessel was supplied, and this was compounded by an inappropriate modification undertaken by the vessel operators to provide consistency. Any modifications need to consider all aspects of the application being altered. In this case, the modification did not take account of the full operational functions of the vessel and inadvertently allowed the supply fan flaps to close under adverse environmental conditions.
- The vessel’s power plant could have consumed more than a cubic metre of air every 3 to 4 minutes. The decision to relieve the pressure differential in the engine room by opening an internal door took due consideration of the environmental conditions on the upper deck but underestimated the differential pressure between the ambient atmospheric pressure and the induced vacuum within the engine room.
