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Fire protection on an FPSO will be a mixture of active and passive protection. Active protection is provided by fire water (deluge, sprinklers, monitors, hose reels), foam, C02 blanketting and portable extinguishers.

Passive protection is provided by the use of fire rated partitions and by fire resistant coatings applied to primary structural members, bulkheads, decks, framing, equipment foundations, and pressure vessel shells, saddles and skirts. Protection may also be required on structures, e.g., the flare tower and turbine exhaust supports, whose premature collapse on to other structures and equipment may result in escalation of an event

The type and extent of each method of protection will be determined by the outcome of fire and other safety related studies. While estimates of fire-water coverage developed at the start of FEED can give a reasonable guide to the sizing of the firewater pumps for the early placement of purchase orders, the extent of passive protection takes much longer to assess. The timing of these studies is therefore important to enable realistic workscopes for the supply and application of passive protection to be developed.

Close liaison between safety and loss prevention engineers and process engineers is desirable for the development of fire scenarios, the outcome of which may indicate that in some areas of the FPSO, blanket deluge or extensive passive protection is not always necessary in the control of fires and the preservation of structural integrity. In certain areas, which in the past might have been provided with sprinkler coverage, it may be possible to provide adequate protection against the size and types of fires anticipated using strategically placed hose reels and hand held extinguishers appropriate to the type of fire.

Once the number and extent of fire zones have been established, then it becomes possible to determine the full extent of water coverage and passive protection for each zone.

Active Protection

Various aspects of the design of the main firewater system such as pumps and metallurgy have been discussed above in section 3.7.2. The following section deals briefly with peripheral equipment.

In areas which are deluge protected and /or hoses and monitors are used, it is essential that insulation, (thermal, acoustic, passive fire protection) on equipment, piping and structural members or panels, is designed and installed to withstand the deluge water forces. Insulation should also be impermeable to firewater and seawater to prevent corrosion under it.

The numbers and size of deluge valve sets will be determined by the water demands of individual fire zones. (Large sets frequently require more space than had been initially

allocated for them in preliminary layout studies). They also have to be positioned away from the area which they serve and suitably shielded to ensure that they are not rendered unserviceable by the event they were intended to be used against.

Although deluge valve sets have been features of active systems offshore for many years, it is still possible to encounter problems of metallurgy and the design of small bore piping (see section 3.7.2 above). The choice of materials for valves and valve components exposed to seawater should be agreed with the project corrosion adviser to avoid mixes of materials which can give rise to early corrosion. Rubber lining of seats, discs and gates as a means of protecting somewhat inferior, cheaper materials may break down resulting in high rates of localised corrosion.

Flushing of subheaders with fresh water after in service testing will help to prevent pitting of cupro-nickel pipework. Deluge nozzles orifices should be sized not only to provide the required coverage and spray pattern but to avoid blockage by foreign bodies or by salt deposits. The choice of metallurgy is also important to prevent corrosion which could render the nozzle(s) ineffective.

The choice of metallurgy is also important for the monitors, hydrants and hose reels to be used on seawater duty. Hose reels will be found mostly inside in the living quarters and machinery spaces. The standards for the supply pipework for the reels and for the valves and fittings should be the same as those for the rest of the firewater system.

Foam for rapid knock-down of fires will be aqueous film forming foam (AFFF). There is still discussion within the industry about the merits of 1% and 3% foam concentration and so the choice will depend on the preference of the operator’s fire and safety engineers.

The selection and location of hand held extinguishers will be determined by the size and nature of the fire which might be expected in a given area.

The use of inert gas for extinguishing fires is now confined to carbon dioxide. The use of halon gas and other similar chlorofluorocarbon (CFC) extinguishants has been banned by international convention, i.e. the Montreal Protocol.

Carbon dioxide is used mainly in the enclosures of gas turbines. Special precautions have to be taken during entry to turbine enclosures to prevent the exposure of personnel to CO2 in the event of spurious activation of the system.

Where halon flood was once used in switch rooms to extinguish electrical fires, it is now possible to have simpler active protection using hand held extinguishers only. A combination of panel design and strategically placed smoke and heat detection providing early warning can contain a fire and permit early intervention through electrical isolation and follow-up use of hand held units.

Passive Protection

In the event of an explosion, the deluge system for the affected area may be damaged to the extent that it cannot offer any protection. Passive protection therefore becomes the only protection against progressive collapse of structure and equipment until such time as:

• the source of fuel has been isolated

• the fire brought under control by depressuring of the production facilities • disposal of inventory, where that its possible

• the use of water or foam from other source

Passive protection can be provided by partitions, suitably rated for the anticipated type of fire, and by coatings. The use and ratings of partitions e.g. H120, A60, B15 etc, are covered in the Classification Society Rules as follows:

• Lloyds Register (ref 22) , Part 7, chapter 3, section 2. • ABS (ref 24), chapter 4, section 8, subsection 9. • DNV (ref 73) OS D301, chapter 1.

Where coatings are used to protect critical equipment and structures, the coating system must be

• Able to withstand the impact of firewater deluge and fire hose jets • Able to remain intact following an explosion

• Able to withstand jet fires • Non-combustible

• Flexible to accommodate movement of structural members and equipment due to flexing of the FPSO hull.

• Impervious to seawater, firewater, hydrocarbons and corrosive chemicals • Chemically inert to prevent degradation over time

• Able to absorb impacts from tools etc without spalling

Consideration has also to be given to the method of application as some passive coatings systems are more labour intensive than others e.g. trowelled on vs spray application. Some may also require a supporting mesh structure to hold them in place.

The use of cementitious materials is not recommended due to unsatisfactory flex characteristics and a tendency to spall on impact.

Additional short term “passive protection” against thermal radiation for personnel escaping from a fire can be provided by the use of strategically placed mesh screens of proprietary design. These screens also provide a degree of weather protection in exposed places such as the turret structure.