Important feedback for Norwegian FPSO design

The ANP (Brazilian authority) investigation report from the accident with Cidade de São Mateus FPSO explosion and fire in February 2015 is tragic and interesting reading. But there is a message from this devastating accident, which is very crucial from a Norwegian perspective, and which is not at all addressed in the investigation.

Norwegian FPSOs, irrespective of being purpose built or converted, have accommodation in the bow of the vessel, as well as helideck also in the bow. Most of these vessels also have no pump room, but deep well (submerged) pumps in each tank. These are special features which outside the Norwegian sector are quite uncommon.

Individual submerged pumps are much more expensive, but are intrinsically safe because there is no possibility for explosion and fire when the pump is submerged in hydrocarbons. Pump room explosion has been one of the most important hazards on commercial tankers for a long period.

Moreover, if the quarters are in the stern of the vessel, the superstructure will inevitably be in close proximity to pump room and engine room(s), as well as downwind of any source of fire or explosion in the hydrocarbon process and storage areas. The pump room, if an explosion occurs, is designed to vent its overpressure on the main deck, in order to avoid puncture of the hull. Thus it is designed to vent the overpressure next to the quarters, when placed in the stern of the vessel.

Both these two factors are fundamental design factors which contributed to the Cidade de São Mateus FPSO explosion and its large death toll (total of 9 fatalities). Without a pump room there might not have been an explosion, without the quarters in the stern the number of fatalities (and wounded) would probably have been reduced significantly.

The importance of these two factors has been confirmed through this accident. It is in fact the first instance we know of where this importance has been demonstrated by actual accidents for FPSOs. It is a valuable experience feedback to note from a Norwegian perspective, and perhaps for others also to take lessons from. Many international FPSO designs (also new built vessels) in recent years have been quite stunning, with what appears to be so little emphasis on protection against effects of explosion and fire.

News, R&D