Marine Auxiliary Machinery 7E Episode 12 doc

430 Fire protection Figure 14.11 Carbon dioxide system required quantity of gas is released into the space within two minutes of actuating the system release. In the installation shown, the actuating handle opens pilot cylinders of CO 2 and the gas from these pushes the piston in the servo-cylinder down, to operate the gang release for the other bottles. To avoid sticking, all the handles must be in good alignment. The bottle valves may be of the quick-release type (Figure 14.13) where the combined seal and bursting disc is pierced by a cutter. The latter is hollow for passage of liquid CO 2 to the discharge pipe. An Fire protection 431 Figure 14.12 CO 2 cabinet alarm alternative type of quick release valve (Figure 14.14) is held in place by a hinged linkage arrangement until released. Bottle pressure is normally about 5 2 bar (750lb/in 2 ) but this varies with temperature. Bottles should not be stored where the temperature is likely to exceed 55°C. The seal/bursting discs are designed to rupture spontaneously at pressures of 177 bar produced by a temperature of about 63°C. The master valve prevents CO 2 released in this way from reaching the engine room. Gas is released by the relief arrangement on the manifold, into the CO 2 space where, in the event that the release was caused by a fire in the compartment, the fire would be extinguished. Rapid injection of CO 2 is necessary to combat an engine room fire which has attained such magnitude that the space has to be evacuated. Hence the rule that 85% of the gas must be released within two minutes. The quantity of gas carried (a) must be sufficient to give a free gas volume equal to 40% of the volume of the space except where the horizontal casing area is less than 40% of the general area of the space, or (b) must give a free gas volume equal to 35% of the entire space, whichever is greater. The free air volume of air receivers may have to be taken into consideration. The closing of all engine room openings and vent flaps will prevent entry of air to the space. All fans and pumps for fuel, can be shut down remotely as can valves on fuel pipes from fuel service and storage tanks. CO 2 bottles are of solid drawn steel, hydraulically tested to 22 8 bar. The 432 Fire protection Figure 14,13 CO 2 cutter type quick release contents are checked by weighing or by means of a radioactive level indicator. Recharging is necessary if there is a 10% weight loss. Pipework is of solid drawn mild steel, galvanized for protection against corrosion. The syphon tube in the bottle ensures that liquid is discharged from the bottles. Without the syphon tube the CO 2 would evaporate from the surface giving a very slow discharge rate and, taking latent heat, would probably cause the remaining CO 2 in the bottle to freeze. Walter Kidde CO 2 system Figure 14.15 is a schematic layout of a Walter Kidde CO 2 system in which pilot CO 2 cylinders are used to open the distribution system main stop valve and subsequently the valves on the individual cylinders. The system shown has two banks of cylinders. The pilot CO 2 cylinders are contained in a control box and normally disconnected. To operate the system a flexible pipe fitted with a quick action coupling is plugged into a corresponding socket. When the valve on the pilot cylinder is opened the pilot CO 2 will open the system main stop valve. The stop valve actuator is a piston device and when the piston is fully Fire protection 433 Figure 14.14 Valve type release depressed a second port is exposed which allows the pilot gas to flow to the CO 2 cylinder bank and to operate the cylinder valves. As soon as the control cabinet door is opened to do this, the alarm is initiated. The position of the hoses in the quick-coupling housings prevents the door from being closed. The pilot CO 2 cylinders and the main CO 2 cylinders for this system, are fitted with Kiem valves. An isometric sketch of a Klem valve fitted with a CO 2 actuator is shown in Figure 14.16. The safety pin shown is for transporting the cylinders. When installed the safety pins are removed from the valves, allowing them to be operated manually or by pilot pressure. As soon as mechanical or pilot pressure is removed, the valve will close again. In this system each of the cylinders is fitted with a CO 2 operated actuator. Low pressure CO 2 storage In some installations, the CO 2 is stored in low pressure refrigerated tanks. The cylindrical storage vessels (Figure 14.17) are fabricated to the pressure vessel requirements of the authorities. The tanks are of low temperature steel, fully tested and stress relieved. They are mounted on supports designed to withstand shock from collision. The insulation to limit heat ingress into the CO 2/ which is stored at a temperature of — 17°C, is polyurethane with fire resistant additives, foamed in situ. Figure 14,15 A CO 2 fire extinguishing and smoke detector installation (The Walter Kidde Co, Ltd) Fire protection 435 Figure 14.16 Klem valve with pressure actuator (The Walter Kidde Co. Ltd) Figure 14.17 Distillers low-pressure refrigerated storage tank Two refrigeration compressors connected to separate evaporator coils mounted inside the pressure vessels, maintain the CO 2 at the required temperature of — 17°C. One unit is sufficient to deal with heat ingress into the CO 2 the other unit is a stand-by. Either water or air cooling can be arranged. 436 Fire protection The duty from main to stand-by unit can be reversed to equalize running hours, 'The instrument panel contains tank contents gauge, pressure gauge and alarms to indicate CO 2 liquid level and pressure and also contains the refrigeration controls, To ensure that a dangerous high pressure condition does not exist if a serious refrigeration fault develops, pressure relief valves are fitted discharging directly to atmosphere. The valves are mounted on a changeover valve and are set to discharge CO 2 gas if the pressure in the vessel rises above the design pressure of 23.8 bar. Each valve can in turn be isolated for removal and periodic testing. The vessels are fitted with a capacitance type continuous indicator together with a stand-by liquid level indicator which ensures that CO 2 liquid level can always be checked approximately by opening the stand-by liquid level indicator valve which will flood the pipe to the same level as the pressure vessel. A frost line will appear due to the low temperature of the liquid CO,. Closing the valve will cause the CO 2 to vaporize back into the pressure vessel The filling and balance lines are normally run to the main deck port and starboard sides for hose connections to be made to a road tanker. The balance line is used to equalize pressure with the tanker during the filling operation. The liquid CO 2 discharge is through a 150mm bore pipe fitted with an isolating valve but the quantity of CO 2 discharged into the various spaces is controlled by timed opening of a discharge valve. A relief valve is fitted which will, relieve excess pressure in the discharge pipe should the isolating valve be closed with liquid CO 2 trapped in the discharge manifold. Automatic or remote operation can be achieved by utilizing CO 2 gas pressure from the top ot the tank as the operating medium. Because of the considerably reduced amount of steel, the storage tank compared with cylinders gives an approximate 50% weight saving and because low pressure CO 2 has a greater density than CO 2 at ambient temperature, the volume it occupies is considerably less in terms of deck space. Also, low pressure CO usually costs considerably less than CO supplied in cylinders. A periodical survey of the refrigeration compressors is required by the Classification Societies and this is limited normally to the exchange of pressure relief valves. At intervals of up to 10 years an internal inspection is required via the man-door provided. Halon systems Halons are included in the Montreal protocol as gases with ozone depletion potential (OOP) and must not be specified for use in fixed fire fighting installations. Compared with R12 which has been assigned an OOP of I, Halon 1211 has been given an OOP of 3 and Halon 1301 a figure of 10. Existing fixed halon fire protection systems will need a replacement fire fighting medium for which adaptations will be required. Halon systems with Halon 1301 have been fitted to a large number of ships. Fire protection 437 Haion is the name for halogenated compounds made by the replacement ot hydrogen in methane or ethane with one of the halogens. Fluorine, chlorine and bromine are halogens. Halon 1301 has the chemical formula CF3 Br being known as bromo-trifluoro- methane. It is a colourless, odourless gas with a density five times that of air and extinguishes fire by breaking the combustion chain reaction. Other halogenated hydrocarbons such as rnethylbromide and carbon tetrachioride have been used in the past as fire extinguishing agents but have been banned by various authorities because of their extremely toxic nature. Halon 1301 however, is classed by Underwriters Laboratories as least toxic' (Group 6) and properly applied discharges of the gas allow people to see and breathe permitting them to leave the fire area with some safety. It must be pointed out however, that when Halon 1301 is exposed to flame or hot surfaces above 480°C halogen acids and free halogens having a higher level of toxicity are produced. A self- contained breathing apparatus or a fresh air mask is therefore essential equipment when entering a space which has been flooded with Halon 1301. In some small machinery spaces Halon 1301 systems may be found in which the Halon is stored in a sphere within the machinery space. In larger installations the storage battery is similar to that used in CO 2 systems. The gas may be stored in 67 litre cylinders at a pressure of 40 bars. This equates to 75 kg of Halon 1301. Figure 14.18 shows the release gear used by Fire Fighting Enterprises (UK) Figure 14.18 Halon 1301 cylinder valve with electric actuator (Fire Fighting Enterprises (UK) Ltd) 438 Fire protection Ltd. In this system a cam on the end of the horizontal pin pushes the vertical valve rod downwards, when the pin is actuated. The pin may be moved by a pull wire or by one of a range of electrically or pneumatically operated actuators. As soon as the valve rod opens the cylinder valve, gas from the cylinder is admitted to the top side of the piston and holds the valve open. When the gas pressure falls away a spring below the piston re-seats the valve. Only one cylinder needs to be fitted with the horizontal pin, shown in the illustration. The valves on the other cylinder can be linked to it with small bore copper pipe so that gas from the master cylinder opens all of the other valves simultaneously. Most halon cylinders are fitted with pressure gauges so that leakage can be more readily detected. The cylinders are also fitted with bursting discs Halon system operation The halon release arrangement shown in Figure 14.19 consists of a storage tank, two sets of CO 2 operating cylinders and a manual release cabinet. The halon is stored at a pressure of 14 bar in the holding tank, which has a pressure relief, filling valve and level-indicator. Release procedure is much the same as for CO r When the cabinet is opened, the alarm operates, fans stop and dampers or vent flaps will close. With all entrances closed, the handles (1) and (2) are operated in succession. Handle (2) can only be moved when released by the blocking mechanism. The contents of the CO 2 bottles opened by handle (1) pressurize the pipeline between the halon tank and the master valve causing the bursting disc to rupture and allowing the halon to flow as far as the master valve. The pressure build up in this line acts on the blocking device to permit operation of handle (2). The latter opens the master valve to the engine room distribution pipe and also opens the CO 2 bottles (2). CO 2 from these ruptures the bursting disc at the top of the storage tank and then assists in expelling the halon. The discharge must be completed in 40 seconds but the alarm sounds as the cabinet door is opened. Personnel must evacuate the space when warned. The 5% concentration gives a risk because the gas is toxic and must be treated with the caution as CO 2 . Multi-spray system for the machinery spaces This system is similar to the sprinkler used in accommodation areas but the spray heads are not operated automatically. The section control valves (Figure 14.20) are opened by hand to supply water to the heads in one or more areas. Ready to use hoses can also be supplied. Fresh water is used for the initial charging and the system is brought to working pressure by means of the compressed air connection. The air bottle provides a cushion and prevents cut-in of the pump due to any slight leakage of the water. The pump is automatically operated by pressure drop in the system when the control valve to one section is opened. Fire protection 439 Figure 14,19 Halon system release The pump must have either an independent drive or an electric motor with a supply via the emergency generator switchboard. It must be able to maintain working pressure when supplying all the sections simultaneously in one compartment. It is installed outside the compartment it serves. Spray nozzles are designed to give the correct droplet size for fires in flammable liquids such as fuels and lubricating oils, when working at the correct pressure. They are located so as to give adequate water distribution over the tank top and all fire risk areas. [...]... extinguish oil fires on the tank top in the machinery space, or above the machinery and over such vulnerable auxiliaries as the oil fuel plant and any other surface in the machinery compartment over which oil is liable to spread Figure 14.21 shows a twin tank venturi proportionator unit This installation is typical of the kind of equipment that has been used in the machinery spaces of older ships, or for... the foam making nozzles in the machinery space or to the foam monitors on the cargo tank decks of oil tankers The capacity of the foam liquid tank is determined by the area of the surface to be covered with foam and is sufficient to deposit foam to a depth of 150 mm Figure 14.21 Automatic foam compound proportioning by venturi 442 Fire protection over this area in a machinery space or a specified quantity... solid drawn steel cylinders under pressure, or at low temperature and moderate pressure in large bulk storage tanks In systems designed for cargo space and machinery space protection, the cylinders will be arranged for a ganged total discharge to the machinery space and limited discharge of one or more cylinders (usually by manual release) to individual cargo spaces, depending on the volume of each space... solutions mix with the reaction: A12(SO4)3 + 6NaHCO3 = 2A1(OH)3 + 3Na2SO4 + 6CO2 The chemicals react in much the same way as those in the soda-acid extinguisher but the action is slower, giving time for bubbles to form Foam-making substances added to the sodium carbonate determine the nature of the foam formed The ratio of the foam produced to liquid is in the order of 8:1 to 12: 1 Because the extinguisher... liquid and filled with the water which has forced it out Water will issue from the nozzles unless the water control valve on the inlet side of the venturi is closed at this point For vessels having two machinery spaces, one foam-making liquid tank and venturi may be fitted, with distribution valves to discharge the foam to either space, or twin tanks can be installed (one for each space) In these systems... diagrammatic drawing of this type of installation is reproduced in Figure 14.23 When the CO2 is released into the head-space of the tank, the solution is expelled to the foam distributor network in the machinery or other space to be protected The capacity of the tank and the number of CO2 cylinders will depend on the area to be protected Automatic foam liquid induction (tankers) A flexible foam liquid... foam maker sprinkler system Solution storage tank Drain valve Level cock Safety vaive M Pressure gauge N Stop value P CO2 supply from cylinders Q Distribution valve R Solution supply to branchpipe in machinery space S Solution supply to foam-makers T CO,, cylinders 444 Fire protection Figure 14.24 Automatic foam compound induction system all flow conditions The atmospheric type foam liquid tank enables... High expansion foam High expansion foam (Figure 14.26) is generated by blowing air through a mesh which has been wetted by a solution of foam concentrate in water It has Fire protection Figure 14.25 445 Marine jet-master foam monitor (Chubb Fire Security Ltd) been used for hold protection on some container vessels and has been tested for engine room fire fighting The mesh is corrugated and its hole size... out; then recharged with fresh water and air Where an automatic system is not fitted in accommodation spaces, it is necessary to install an automatic fire alarm system similar to that used for unmanned machinery spaces The system would consist of an electric circuit for srnoke detectors and possibly bimetallic temperature sensors Warning is given by an audible alarm with visual indication showing the... together with the foam liquid venturi fed by a dual water supply from the ship's pumps Sometimes single tank units are fitted The foam liquid tanks are located at a suitable and approved position outside the machinery space; the capacity of the tanks depends on the surface area to be covered and the depth of foam required The venturi to which the dual water supply from the ship's pumps is led is fitted beneath . on the tank top in the machinery space, or above the machinery and over such vulnerable auxiliaries as the oil fuel plant and any other surface in the machinery compartment over. been flooded with Halon 1301. In some small machinery spaces Halon 1301 systems may be found in which the Halon is stored in a sphere within the machinery space. In larger installations . specified for use in fixed fire fighting installations. Compared with R12 which has been assigned an OOP of I, Halon 121 1 has been given an OOP of 3 and Halon 1301 a figure of 10.