Automatic Foam Compound Induction System for Fire Fighting on board Ships
Most of the ships especially tanker ships uses foam fire extinguisher on deck as fixed fire extinguishing system. In portable foam fire extinguishers, foam solution (Foam concentrate and water in a definite proportion) is filled inside which is expelled out with CO2 cartridge fitted inside. In fixed foam extinguishing systems, a separate foam concentrate tank is used, which is mixed with sea water in a definite proportion and used against fires. This proportional mixing is achieved with the aid of automatic foam compound induction system.
Different types of systems are used. One of them is explained here. Automatic inductor unit is fitted at the suction line of the fire pump. Sea water is fed to the pump through a main strainer and inductor unit. Also one line is tapped from pump discharge line, back to inductor unit as driving liquid. Foam is fed to the inductor unit through a non-return valve as shown in the figure. While running, inductor unit ensures proper mixing of foam compound with water. Prepared foam mixture is pumped to different foam monitors branched out.
Foam is produced only at delivery points (Foam Monitors). Because well mixing with air is essential for the production of good quality foam. This happens at the foam monitor, which sucks air when foam is expelled out. Foam monitors can be rotated 360 degrees and moved up and down, which offers a wide operating area.
Since fixed fire extinguishing system is the only fire extinguishing system that can handle large fire hazards, its scheduled maintenance is very important. Usually a small pump is fitted to the foam tank, which sucks foam solution from tank and deliver it back. This re-circulation of foam is usually carried out once in a week. Similarly foam sample is to be taken at intervals and sent to laboratories for testing contamination or change of properties. All the pumps, valves and mechanisms associated with the system to be tested periodically for satisfactory operation. Sea water strainer and foam liquid strainer to be cleaned to ensure trouble free operation.