Fire on board the Union Rotorua

Summary

The New Zealand registered roll on/roll off, gas turbine/electric ship Union Rotorua was about 27 miles south of Sydney Heads, en route for Melbourne, when a fire broke out in the gas turbine house.

It was established that the seat of the fire was in one of the cubicles of the 6.6 kilovolt switchboard, which distributed power from the gas turbine generator to the propulsion motors and auxiliary electrical systems.

Initial attempts to fight the fire with extinguishers proved to be ineffective and a decision was made to utilise the fixed firefighting medium and flood the space with CO2.

This was effective in extinguishing the fire. With the high voltage switchboard out of commission, the vessel was towed to Sydney, where it remained for three months undergoing repairs.

Conclusions

1. It was not possible to establish the exact cause of the fire, although evidence indicates that it probably started in the yellow phase of the main generator circuit breaker at the lower "tulip", connecting the generator input to the circuit breaker.
2. Initiation of the fire at the "tulip" connector may have been due to high electrical resistance caused by one or more of the following:
   • Loss of spring pressure (due to age or other causes) behind the connecting "fingers" of the "tulip".
   • Oxidation of the contact surfaces due to loss of silver plating on the contacts.
   • Mechanical fracture, due to vibration, of the end of the circuit breaker's connecting post at the point of change of cross-sectional area.
   • Loosening or fracture (due to vibration) of the socket-head cap screw securing the aluminium alloy collar mounting the connecting "fingers", to the end of the copper post.
3. Although the Electrician's workbook noted, in June 1991, that the contacts on the "Main HT breaker" needed re-silvering, there was no indication that this was ever carried out.
4. The fire spread to the adjoining cubicle containing the circuit breaker for the no.1 ship's service transformer. This may have been due to ionisation of the atmosphere by products of combustion from the fire in the main generator circuit breaker cubicle.
5. The Inspector considers that the delay in shutting down the gas turbine generator, after the fire was discovered, was excessive, but that the actions of the ship's officers and crew in tackling the fire were prompt and correct in all other respects.
6. The emergency response was effective and demonstrated planning and procedures of a high standard.