How it happened
When the crew was burning of sludge in the vessel incinerator, the exhaust gas temperature alarm was a little high; This resulted to smoke coming from the incinerator exhaust gas manifold, following a fire inside the exhaust pipe.
Specifically, as IMCA presents:
19:34: the alarm sounded, and the crew mustered. The vessel course was altered to prevent the spread of smoke. The team commenced the cooling of the funnel and entered the incinerator room with extinguishers to fight the fire but were unable to extinguish it.
19:41: the fire team left the incinerator room and sealed the door. Later on, the sprinkler system for the incinerator room was activated.
20:01: the fire extinguished and the sprinkler system was stopped.
According to the report, the smoke and the high temperature remained over an hour. That's why, the team continued the boundary cooling until the situation was stabilised at about 21:00. A fire watch was maintained until midnight.
The incinerator was only used for burning sludge, at a temperature somewhere between 810-850°C. For some reason the flame extinguished.
According to IMCA:
- The set point value on a control resistor was set too low, such that the equipment was not able to detect that the flame had failed, and so kept pumping sludge into the combustion chamber;
- The temperature decreased slowly to below 810°C; at that point the automatic diesel burner triggered and started its cycle – the burner ignited and started burning fuel;
- This re-ignited the hot sludge already in the combustion chamber and caused a ‘fireball’ inside the exhaust pipe;
- This in turn caused the exhaust temperature to rise, which triggered a high exhaust gas temperature alarm;
- This stopped the sludge system from pumping more sludge into the incinerator, and the system should then have started to cool down;
- Since there was an accumulation of sludge left inside the combustion chamber, the sludge just kept on burning and the temperature continued to rise;
- After five minutes, the emergency stop button was activated and this cut the power to the incinerator, and all fans stopped;
- There was still sludge left inside the burning chamber floor, which continued to burn unassisted;
- Since the flue gas fan was not running, the exhaust started going out through ventilation holes on the incinerator and this triggered the smoke detectors inside the incinerator room.
Factors that caused the incident
Following, the investigation resulted that the set point value on a control resistor was set too low; Therefore, the equipment was unable to detect a flame failure.
Also, the exhaust sensor had been tampered with.
- Conduct a full, detailed and comprehensive understanding of what happens to incinerators and other similar equipment when the emergency/stop button is pressed, and/or when power fails and restarts.
- Ensure that incinerator flame failure devices are tested as part of the vessels’ planned maintenance system.