The auxiliary oil-fired boiler burner limit switch (burner swing out limit switch), was giving trouble with its electrical contacts. Thus the 2nd Engineer and the Electrical Officer planned to change the electrical limit switch at the departure port, as the cargo operation was going. Due to tight loading schedule and hectic work pressure, the risks involved were not assessed specifically for this job. One of the previous generic risk assessments was used and discussed. The entire low voltage electrical isolation permit was filled up and the tool box talk carried out. The cargo operations completed, and the vessel sailed towards the discharge port.
After clearing the maneuvering area, when full away was ordered, the main propulsion engines reached the maximum rpm, and the steam plant stabilized as the economizers started steaming as required. The auxiliary boilers oil firing section was stopped. Since the oil firing section was not being used (the economizers being capable of coping with the sea-going steam demand), the auxiliary boiler control voltage was switched off and “Locked out for life". The 2nd Engineer and the Electrical Officer started the work with the permits and proper isolation.
After ten to fifteen minutes, the duty engineer (4th Engineer) came up to 2nd Engineer and said that the steam condensate hot well tank was overflowing. Both of them started checking for the cause and could not find it. All the expansion tanks’ levels, the condenser for sea water leakage, and many other checks were done, but no clue about the overflowing hotwell was revealed. The situation was so bad that for every 30 minutes, approximately ten cubic meter of water was overflowing to the bilges and thus increasing the engine room bilge accumulation. The 2nd Engineer decided to complete the job of replacing the limit switch and instructed the 4th Engineer to look for the cause.
After about an hour, there was a steep rise in steam pressure, which caused the 4th Engineer to alert the 2nd Engineer. Both rushed to the engine control room to monitor further happenings. The Navigational watch keeper from bridge called up the engine room to inform about heavy sparking and black smoke coming from the funnel. The 2nd Engineer reported the issue immediately to the Chief Engineer, who decided to slow down and stop the main propulsion engine.
Even though the main engine RPM was gradually reduced, the sparking and black smoke from the funnel did not respond positively. The main propulsion was then stopped. As propulsion stops, the auxiliary boilers have to be fired to maintain steam pressure. After rectifying the limit switch on auxiliary boiler #1, when the control power to the burner was turned on, the boiler remote and DCS readings showed low water level alarm and trip. The Engineers rushed to the boiler to check the water level locally. The gauge glass was checked for the water level, which ultimately showed nothing. The Engineers did not figure out how this happened. The Chief Engineer immediately summoned everyone for a meeting and discussed the series of events which occurred. The ship was brought to complete standstill position.