Marine Fire Suppression Systems: What Changes on a Vessel or Offshore Platform

Fire suppression at sea is the same physics as on land with three things changed. The approvals are different: a unit on a US flagged vessel or a platform on the outer continental shelf needs US Coast Guard acceptance and, for most offshore assets, class society approval from ABS, DNV or Lloyd's, rather than a UL listing alone. The environment is harsher: salt spray, constant vibration, deck wash and a maintenance crew that is small and far from a depot, which pushes every component toward 316 stainless, marine coatings and sealed enclosures. And the hazards are packed together: wellbay, process, fuel, helideck, machinery and accommodation can sit within 150 ft of each other on a platform, so the suppression plan is drawn zone by zone and the agents differ from deck to deck. Each of those changes lands on the specification, and a fixed dry chemical system earns its place on a particular set of decks.

Who approves a marine fire system

Onshore, the authority having jurisdiction accepts a UL listed unit designed to NFPA 17 and signs off. At sea there are two more authorities. The flag state sets the legal requirements, and for a US vessel or US waters that is the Coast Guard under 46 CFR, which carries both the fixed system requirements and the equipment approval series. Internationally, SOLAS Chapter II-2 and the Fire Safety Systems Code carry the equivalent rules, and for gas carriers the IGC Code specifically requires a fixed dry chemical powder system covering the cargo area. Fixed production platforms on the US outer continental shelf answer to the Coast Guard as well, under 33 CFR Subchapter N, with API RP 14G commonly cited for fire prevention and control on the production equipment.

The second authority is the classification society. ABS, DNV and Lloyd's Register each have rules for fire extinguishing systems on vessels and offshore units, and an insurer or charterer expects class approval of the equipment plus a surveyor's witness of the installation and commissioning. Class approval is a separate process with its own type approval certificates, and holding one does not mean holding the other. A procurement team asks a supplier three separate questions, UL listed, Coast Guard approved and class type approved, and reads each answer on its own. Salus Global skids are UL listed to UL 1254, and Coast Guard approval for offshore use is in progress; the status of class approval should be confirmed for the specific society and project.

Materials and construction for salt, vibration and neglect

Corrosion is the design driver. A painted carbon steel agent tank lasts decades in a Texas tank farm and a few years on a weather deck in the Gulf of Mexico. Marine specification moves the wetted and exposed parts to 316 stainless: tank, manifold, valves, fittings, nozzle and hose couplings, and the frame or at least its hardware. Where 316 is impractical, as on the nitrogen cylinders, which are usually steel, the answer is a marine coating system, typically a zinc-rich primer under an epoxy and polyurethane topcoat to the ISO 12944 C5 or CX corrosivity class, with cylinder brackets isolated from the cylinder to stop crevice corrosion under the clamp.

Enclosures are the second item. A skid on an open deck is hit by spray and green water, and a dry chemical agent that takes on moisture cakes and will not fluidize. Marine units use sealed tank fills and inspection ports with stainless closures, pressure relief fittings that exclude water, and, on platforms, often a stainless or GRP cabinet over the entire skid with louvered ventilation and a drain. Vibration loosens fittings and fatigues tubing over years, so marine units use closer tube clamp spacing, thread-locked fasteners and flexible hose at the cylinder connections. The last factor is the crew: every inspection point has to be reachable without rigging and every consumable has to be a part the supply boat can carry.

The platform, deck by deck

A production platform's suppression plan reads like a map. The helideck is protected by foam, usually a deck integrated system with pop-up nozzles or perimeter monitors, because a helicopter crash is a running fuel fire across a flat deck and foam is the only agent that blankets it. The process deck, where separators, compressors, pumps and the flare knockout drum live, is the dry chemical zone: pressurized gas and three-dimensional hydrocarbon fires at flanges, seals and relief points, which foam cannot hold and water cannot extinguish. A fixed dry chemical system with nozzles aimed at the high risk points, or skids with hose reels placed so that two units cover every part of the deck, is the typical arrangement, with deluge on the vessels for cooling and on the structural steel for exposure protection.

The wellbay and drill floor are protected with dry chemical, because a well control incident that ignites is a gas jet fire, backed by deluge for cooling and for keeping the escape routes usable. Machinery spaces, the enclosed rooms holding the generators, engines and switchgear, are protected by total flooding: CO2 historically, now often water mist or a clean agent where the space is regularly occupied, under the SOLAS and 46 CFR rules for enclosed machinery. Accommodation gets sprinklers or water mist, fuel storage gets foam or deluge depending on the tank type, and the crane pedestal, lay-down area and boat landing get portable and wheeled units.

Fixed DCP systems on ships and where they fit on a platform

On a gas carrier the fixed dry chemical powder system is required equipment. The IGC Code calls for at least two independent self-contained units covering the whole above-deck cargo area, with monitors rated at 10 kg per second or more and hand hose lines at no less than 3.5 kg per second, and enough powder in each container for 45 seconds of discharge through everything attached to it. Those systems are built like a land-based fixed DCP system, with a large agent vessel, manifolded nitrogen cylinders, distribution piping to monitors and hose stations, and remote release from the cargo control room. What changes is the materials, the approvals and the fact that the ship cannot call for help.

A platform uses the same architecture where the hazard is fixed in place. A fixed dry chemical system with an agent vessel in the 2,000 to 4,000 lb range and piped nozzles over the compressor skid or the wellhead gives automatic or remote release on a gas fire without a person on the deck, which on a normally unattended installation is the only option. Where the hazard moves, such as a drill floor during well intervention, a crane laydown area or a process deck with many small targets, the answer is a skid. Salus Global dry chemical skids in 350, 1,000 and 2,000 lb capacities are UL listed, hold nitrogen in separate charged cylinders at 150 to 200 bar so the ASME Section VIII agent tank sits unpressurized until actuation, and are manual, stand-alone units with a hose reel and nozzle. Marine duty calls for stainless components and a marine coating system, so confirm the material options when specifying. The fluidization design that gives the fast knockdown and high flow rate on land counts for more at sea, where vibration packs a settled charge. Purple K is the usual agent for the hydrocarbon hazards on a platform, and the architecture follows the hazard: piped nozzles for fixed equipment, a skid where work moves.

The limits of dry chemical offshore

The same honesty applies at sea as on land. Dry chemical does not cool, so a compressor casing or wellhead that has been burning for several minutes can reignite from the hot metal once the powder settles, and the tactic is to follow the knockdown with isolation and deluge cooling. Wind is a larger problem on a platform than anywhere onshore; a 25 knot wind across a process deck will carry a dry chemical cloud away from the fire, so nozzle placement and hose reach follow the prevailing wind and the operator approaches from upwind. Residue is a maintenance cost, and the monoammonium phosphate in ABC agents is corrosive to electrical equipment, which is why ABC is rarely specified on a platform. And dry chemical is not a total flooding agent: it is not used in machinery spaces or accommodation, where CO2, water mist and clean agents do the job.

Maintenance at sea follows NFPA 17 for the dry chemical equipment, with the monthly visual inspection and the semi-annual agent examination carried out by the platform technicians and logged for the class surveyor, and two retest clocks: the agent tank at 12 years, the separately stored nitrogen cylinders on the DOT 5 year requalification, 10 only if star marked, both planned around the dry dock or major shutdown. Class surveys want to see the records at each annual survey and will periodically witness a functional test of the release system or a discharge test, so it needs fill ports and cylinder connections a technician can manage on deck after a test discharge.

Frequently asked questions

Is a UL listing enough for an offshore platform?

No. UL 1254 listing tells the Coast Guard inspector and the class surveyor that the unit performs as a pre-engineered dry chemical system, and it is the base document, but a US platform needs Coast Guard acceptance of the equipment under 46 CFR and, in most cases, class society approval of the equipment and the installation. Ask the supplier for the status of each separately.

What materials should a marine dry chemical skid be built from?

316 stainless steel for the agent tank, manifold, valves, fittings and hose couplings, a marine coating system on any carbon steel parts including the nitrogen cylinders, isolation between dissimilar metals, and sealed fill and inspection ports. A cabinet over the skid is common on open decks.

Why do gas carriers use dry chemical rather than foam on deck?

A cargo deck fire on an LNG or LPG carrier is a pressurized gas or vapor fire at a manifold, valve or vent, not a pool fire, and dry chemical, usually potassium bicarbonate, is the agent that extinguishes a gas fire by interrupting the flame chain reaction. The IGC Code requires a fixed dry chemical system for the cargo area for that reason; foam and water are used for cooling and vapor control rather than extinguishment.

Salus Global dry chemical skids are UL listed and assembled, filled and inspected at our facility in Texas. Call +1 360 901 9828 or email info@salusglobal.co.