​On May 17, 2025, about 0429 local time, while the chemical tanker Scot Stuttgart was moored at Puerto Nuevo Terminals, in San Juan, Puerto Rico, a fire broke out in one of the vessel’s two engine rooms. Crewmembers deployed the carbon dioxide fixed fire extinguishing system on two separate occasions, extinguishing the fire. There were no injuries, and no pollution was reported. Damage to the vessel was estimated at $333,525.

​We determined that the probable cause of the engine room fire aboard the tank vessel Scot Stuttgart was the crew not isolating a fuel return line during diesel engine maintenance, leading to diesel fuel backflowing from a fuel oil day tank and cascading onto a powered electrical panel or thermal exhaust gas economizer lines, where it ignited. Contributing to the fire damage was the master’s decision to authorize local shoreside firefighters to unseal and ventilate the engine room, which introduced oxygen into the space, reduced the effectiveness of the carbon dioxide released from the fixed fire extinguishing system, and allowed the fire to intensify and burn longer.

​Consulting Vessel Drawings when Isolating Systems for Maintenance

When a crew performs maintenance on a system, improperly isolated fuel, lube, or hydraulic oil piping can result in leaking oil and, potentially, a fire. Referencing vessel drawings can help crewmembers identify all components of a fuel, lube, or hydraulic oil system, as well as potential hazards, such as oil lines or valves that may need isolation before performing maintenance.

Maintaining the Effectiveness of Fixed Fire Extinguishing Systems

Fixed fire extinguishing systems in machinery and other hazardous spaces require a minimum concentration of extinguishing agent to either halt the chemical reaction producing the fire, displace the oxygen feeding the fire, or effect a combination of both. To ensure the effectiveness of the system and prevent the reintroduction of oxygen into a space, the system should be operated so that the required amount of fire suppression agent is released into the space as designed. Additionally, spaces should remain sealed for sufficient time to allow the fire suppression agent to smother fire, as well as for temperatures to drop, for up to 24 hours.