The fire main isolating valve and the emergency fire pump

Why the isolating valve

A fire in the engine room can take out pump No.1, its supply and the fire main around it. So the engine room section of the main has an isolating valve outside the machinery space, where a man can still reach it in a fire. With that valve shut, every hydrant outside the engine room must still get water from another pump or the emergency fire pump (SOLAS II-2/10.2.1.4.1).

The emergency fire pump

On this PSV the emergency fire pump stands in the bow thruster room, with its own sea chest, and runs from the emergency switchboard. In a blackout the emergency switchboard is dead until the emergency generator takes it over, a few seconds later. The pump’s direct-on-line starter holds itself in, so it stops when the emergency switchboard goes dead and has to be started again from the bridge.

Each pump discharges through a screw-down non-return valve (SDNR). With pump No.1 stopped and the isolating valve open, water from the emergency pump reaches the engine room hydrant but cannot run back through pump No.1 to the sea. With pump No.1 running and two jets open, the main sits above the emergency pump’s shut-off head and its SDNR stays shut.

Capacity and pressure

Size (FSS Code, chapter 12): at least 40 % of the total capacity required of the fire pumps, and never less than 25 m³/h on a cargo ship of 2000 GT and over. IMO MSC.1/Circ.1314 reads the hydrant pressure it must hold as 0.27 N/mm². In the simulator’s model it gives 43 m³/h and 3.1 bar with two jets on the forecastle.

The emergency fire pump test

The emergency fire pump test proves the arrangement, not only the pump: isolating valve shut, emergency pump started from the bridge, two jets from the forecastle hydrants at the required pressure. Then the valve goes back open. Left shut, it keeps pump No.1 off the deck at the next fire.

Hoses and pressure

Hoses are at most 15 m long in machinery spaces and 20 m on open decks (SOLAS II-2/10.2.3.1.1). Hydrant pressure must stay low enough for the hose team to hold the branch (10.2.1.6.3); UK surveyors want to see that demonstrated above 7 bar. The amber band on the hydrant gauge starts there.

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