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Design errors led to ahu fire

Petrojarl Knarr
The Petrojarl Knarr

NORWAY: Design errors and faulty operations of an HVAC system have been blamed as the cause of a fire on a floating oil production vessel off the Norwegian coast.

The fire on the Petrojarl Knarr (PJK) was detected in the air handling unit supplying the forward engine room in March of this year. No one was injured as a result of the incident but personnel were mustered in the lifeboats before the fire was extinguished about 30 minutes later.

The air handling unit following the fire

Investigations by the Petroleum Safety Authority Norway (PSA) have revealed that the fire started following a power failure the previous afternoon. The power cut shut down the fans in the air handling unit but steam continued to be supplied to its heat exchanger. That caused high temperatures to develop in the unit, and the air filter cassettes ignited eight hours later.

The fact that the supply of heat did not shut down in the event of the fans halting was regarded as a design weakness with the HVAC unit.

Operations personnel on PJK had struggled for a time with repeated power failures as a result of problems with operating the gas turbines which deliver electricity to the vessel. A lot of equipment on board has to be restarted following this type of failure. The HVAC unit supplying the forward engine room was run in a mode which meant that the fans had to be restarted manually following a power cut. This was not done after the failure which occurred on March 23.

Although the fans had not been restarted, steam from the steam heating system continued to be circulated through the heating coil. Lack of air throughflow as a result of the fan shutdown and heating as a result of the steam supply meant the whole air handling unit heated up. The filter cassettes, which had a maximum design temperature of about 70°C, collapsed as a result of lengthy exposure to a temperature of roughly 100°C. Alarms in the control room from the HVAC unit were not perceived as critical after the power failure the day before. They were given the lowest priority on the screen.

The report can be viewed here.


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