Fire on Offshore Platform Caused by HVAC Unit – Investigation Report

This investigation report refers to the fire that broke out on Songa Dee on 4 December 2007. At 13.52 hours on 4 December 2007, the fire alarm sounded on the Songa Dee. The living quarters and important rooms such as the radio room, control room and emergency preparedness center were efficiently evacuated during the course of a few minutes. The fire was located in HVAC Unit No.2 and large parts of the living quarters were filled with thick smoke from the cooling and filter unit in the HVAC system. No one was injured during the incident, but the rapid, intense spread of smoke means that the incident is classified as a potential major accident.

2013.08.05 - Fire on Offshore Platform Caused by HVAC Unit - Investigation Report

The fire that broke out in the HVAC unit went on for more than an hour before there was confirmation that it was extinguished. It caused significant fire damage to ventilation unit No. 2. Stena estimates that the unit, which consists in part of a fan, motor, heating element, cooler and filter, is 90% damaged. The cooling and filter unit, where the fire broke out, was nearly burnt out.

When the alarm sounded and heavy smoke rolled into several cabins, about 35-40 persons were asleep there. Rapid evacuation resulted in these personnel escaping in time. Large parts of the living quarters and adjoining rooms suffered extensive fire and soot damage. 81 persons were evacuated to land or to other facilities while a safety manning crew consisting of 19 people remained on board. Clarification of the extent of damage, clean-up work and cleaning took place on board for 9 days before normal drilling activity was resumed. Firms with special expertise were hired to measure air quality before the clean-up work was started. The fourth floor of the living quarters was supplied by a separate ventilation unit and was not much affected by the incident. Therefore, the safety manning crew (19 people) used this part of the living quarters until other parts were cleared for use.

The ventilation system that was affected by the incident was inspected and cleaned using special equipment. Some equipment in cabins and dayrooms was replaced to eliminate as much smoke scent as possible.

The Norwegian PSA during its investigation found that the emergency response on board the Songa Dee during the initial phase and the firefighting phase of the incident was not handled in a very satisfactory manner as regards the following circumstances:

  • Inadequate use of and access to radio communication to/from the facility vis-à-vis land and other facilities and units in the area and internal communication via the PA system.
  • The emergency response room had to be evacuated and there was no access to, or there was no use of, a back-up emergency response room with the necessary emergency response equipment and access to monitoring equipment to follow-up the condition of the facility.
  • Finally, the PSA investigation noted the disorganized manner in which firefighting was initiated and carried out, i.e. that personnel who were not part of the fire team started fire extinguishing in an area where there were both heat and electrical sources present and there was no adequate confirmation that such equipment was isolated and switched off.

In addition to the above remarks the PSA investigation report concluded to the issuance of the following non conformities in connection to the fire incident on the platform:

1. Fan shutdown for living quarters ventilation system

Necessary barriers were not established in order to discover and implement necessary measures in connection with failure of the ventilation system for the living quarters. The system is to provide 50 Pascal overpressure in relation to the surrounding environment. This was evident from the following:

  • No pressure sensor or other equipment has been installed to register shutdown of the fan for Unit 2. A transcript from pressure monitoring in the living quarters shows a pressure drop to 50% or less at 13.38 hours. It is assumed that the fan for Unit 2 stopped at this time due to the fan belts that stopped functioning. No equipment was installed to ensure that the motor, heating element, damper, etc. are shut down if the fan stops, in order to prevent overheating and to maintain sufficient overpressure in the living quarters from Unit 1.
  • Each floor in the living quarters had pressure monitoring. Transcripts from the alarm system in the control room showed frequent low pressure alarms (25 Pascal). For example, the alarm transcript showed such low pressure in the 1st and 4th floors at 09.48 hours and 10.30 hours. Low pressure alarms on the second floor were recorded at 10.30 hours and 11.36 hours. At this latest time, the pressure fell to about 10%. It was stated that these alarms were common due to doors being opened.
  • Transcripts from the pressure monitoring in the living quarters showed that, at about 12.40 and 13.18 hours, one of the fan units had failed for several minutes (pressure drop to 50%) without this emerging in the form of alarms to the control room operator. The system was not adjusted so as to give alarms in the event of such failure in the air supply.
  • The control room operator’s handling of alarms (risk understanding and competence).

2. Risk assessments in connection with modifications

Insufficient implementation of risk assessments in connection with replacement of existing HVAC unit to new unit with electrical heating element. This was evident from the following:

  • In 2006, existing HVAC Units 1 and 2 in the living quarters were replaced. This was a planned upgrade of the system since the existing air heater (based on steam), damper and other equipment in the system did not function satisfactorily. The new system was built with an electric heating element for heating. No risk assessments or analyses of the change that was made were conducted.
  • The description of the change work showed which equipment was included in the delivery and who was responsible for installation the equipment. Responsibility for the systemic changes made and documentation requirements were not defined.
  • No risk assessments were performed of control stations (bridge, control room, radio room, etc.) in the living quarters based on this type of incident which can render all such stations inoperable.

3. Design and installation of new fan unit

The new HVAC unit was not designed and installed to enable operation during given system conditions with the possibility of air flow in the opposite direction in the event the fan stopped. This was evident from the following:

  • No fault mode/fault effect analysis (FMEA) was conducted for the new system which illuminates the consequences of failure of the fan belt on one of the systems.
  • The heating element was labeled to indicate the flow direction for air. Placement of thermostats to shut down the heating element in the event of overheating were not favorably situated in order to function if the air flowed in the opposite direction.
  • No measures were instituted to give alarms or shut dampers on the air intake to prevent air flow in the wrong direction.
  • A demister constructed of combustible material was installed in front of the heating element. It had a relatively low ignition temperature and was installed just a few cm away from the heating element. With air flow in the opposite direction from normal, this solution represented a significant fire hazard that had not been adequately analyzed in the design phase.
  • It emerged that the vendor of the HVAC unit recommended a distance of minimum 300 mm between the filter element and the heating element. A corresponding minimum distance between the demister and the heating element had not been defined. However, it did emerge during the conversations with the vendor that, for similar new deliveries, a demister would not be installed in this manner.

4. Inadequate radio and internal communication

The communication systems on the facility and vis-à-vis land, including the VHF/UHF systems internally on the facility and vis-à-vis nearby facilities, were not accessible to the emergency preparedness management and other emergency response personnel in an adequate manner during the initial phase of the incident. This was evident from the following:

  • Statements by interviewed personnel and written explanations confirm, from several sources, that communication with neighboring facilities was not possible, including standby vessel and helicopter, nor could they communicate with land, during the initial phase of the incident.
  • During a short period of time, the central control room and the emergency response center were filled with smoke and gases which prevented access to and use of the stationary communication equipment.
  • Portable VHF equipment had to be collected from the drill floor.
  • In the initial phase of the incident, the PA system could not be used to provide information to the crew on board.

Furthermore the Norwegian PSA identified also the following items as areas which could be further improved:

  • Documentation of the HVAC system
  • Installation of fire damper
  • Collection and processing of alarm transcripts
  • Maintenance management
  • Follow-up and evacuation of personnel involved in the incident
  • After incident investigation procedures
  • Follow-up and evacuation of personnel involved in the incident
  •  Sick bay unable to function – inadequate medical preparedness
  • Emergency response room unable to function – deficient redundancy/back-up emergency response room
  • Emergency preparedness competence for response personnel
  • Capacity problems in connection with refilling respiratory equipment
  • Deficient use of smoke hoods in the cabins
  • Muster routines and registration system for personnel on board

Source: Norwegian PSA

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