DRAW/ REGULATION/MAINTENANCE/SYSTEM DESCRIPTION OF FIXED FOAM FIRE FIGHTING SYSTEM IN SHIP.

EXPLAIN FIXED FOAM FIRE FIGHTING SYSTEM IN SHIP?


=Foam for fire protection purposes ,is an aggregate of air-filled bubbles formed from aqueous Solutions, and is lower in density than the lightest flammable liquids.
=It is mainly used to form a coherent floating blanket on flammable and combustible liquids to Prevent or to extinguish fires by excluding air and cooling the fuel. It also prevents re-ignition by suppressing formation of flammable vapors.
= It has the property of adhering to surfaces, providing a degree of exposure protection from adjacent Fires.
=Foam is used as a fire prevention, control, or extinguishing agent for flammable liquid in tanks of Processing areas
=Foam solution for these hazards may be supplied by fixed systems or portable foam generating Systems.
=The principal use of foam is to extinguish burning flammable or combustible liquid spills or tank fires by developing a coherent coolant blanket.
=Foam is the only permanent extinguishing agent used for fires of this type. Its application allows fire fighters to extinguish fires progressively.
=foam blanket covering a liquid surface is capable of preventing vapor transmission for some time, depending on its stability and thickness.
=Fuel spills may be rendered safe by foam blanketing. The blanket may be removed after a suitable period of time.
=Foam is used to diminish or halt the generation of flammable vapors from non-burning liquids or solids, and to cut off access to air for combustion.
=The water content of foam cools and diminishes oxygen by steam displacement.
=Foam is also used to fill cavities or enclosures where toxic or flammable gases may collect.
=Foam solutions are conductive and therefore not recommended to

electrical fire

How foam extinguishes the fire

Fire fighting foam used on ships has three elements.

• Foam concentrate
• water
• air

Foam concentrate is mixed with water in a correct proportion to form a foam solution. This foam solution when agitated with air produces foam.

Foam extinguishes the fire in three ways

• It forms a blanket and thus removing the supply of oxygen to the fuel, the effect called smothering.
• The foam blanket does not allow the fuel vapors to generate, thus cutting the fuel supply to the fire
• Since foam has water, it cools the fuel surface

Main terms used in defining the foam

Now let us get to know few of the terms associated with foam.

Expansion ratio

We all understand how a foam solution is formed. The form concentrate is mixed with the sea water and air at the foam monitor causes this foam solution to generate foam.

In other words, foam concentrate that we have in foam room tank expands to generate foam. Different foam concentrate has different capacity of how much foam these can generate from a fixed quantity of foam concentrate.

The ratio of the volume of foam generated (finished foam) to the foam concentrate used in that is called expansion ratio of foam.

The foam with expansion ratio between 1:2 and 1:20 is called low expansion foam.

Foam with expansion ratio between 1:20 and 1:200 is called medium expansion foam.

Foam with expansion ratio above 1:200 is called high expansion foam.

Drainage time

IT is the measure of how quickly a foam solution can move over a surface. Foam solution that has lesser drainage time move faster over a surface.

Drainage time is measured for 25% solution and 50% solution. This is called 25% drainage time and 50% drainage time.

Proportioning rate

Foam is generated by mixing foam concentrate with water. For the effective generation of foam that can be effective in firefighting, a correct amount of water need to be mixed with foam concentrate.

This ratio is called proportioning ratio. It is also called mixing ratio or dilution rate.

So 6% foam concentrate means that the ideal foam solution from this foam needs to have 6 parts of the foam concentrate and 94 parts of water.

Knockdown speed and flow

Knockdown speed and flow is the ability of the foam to flow on the fuel and around the obstacles.

Good knockdown speed would mean that the foam is able to flow past the obstacles on the fuel surface.

Type of Foam solutions used on board ships

Broadly all foams fall under one of these two categories

• Chemical foam
• Mechanical foam

Chemical foam produces the foam by chemical reaction of two chemicals, one being alkali and second an acid.

Mechanical foam uses physical agitation of the foam concentrate to produce foam.

On board ships, the mechanical foam is mostly used. There are different type of mechanical foam  used on board depending upon the expected source of the fire.

Let us discuss few of these.

Aqueous film forming foam concentrate (AFFF)

This is the very common type of foam used on board ship specially on tankers.

As the name suggests, apart from the foam bubbles, this foam makes an aqueous film over the surface that spreads across the surface of hydrocarbon to extinguish the fire.

These type of foam works on the fires generated from burning of hydrocarbons.

Alcohol resistant Aqueous film forming foam concentrate (AR-AFFF)

As I said foam has water in it. All the solvents like alcohols are miscible in water. So if we use normal foam on alcohol fires, alcohol will dissolve the water and foam will break up easily.

So for extinguishing the fires involving solvents like alcohol, normal foam concentrate will not do.

For fighting the fires involving alcohols and other solvent alchohol resistant foam is required.

On chemical tankers, that have foam as fixed fire fighting system for cargo fires, alcohol resistant foam is a must. This is because these ships carry alcohols (like Methanol, ethanol) as cargo.

So next time we check the foam certificate on a chemical tanker, we must look for the information mentioning the foam to be alcohol resistant.

Foams based upon the expansion ratio

We discussed that there are three types of foams based on the expansion ratio.

• High expansion foams
• Medium expansion foams
• Low expansion foams

But which foam will be used where ?

Would’t it be the fact that high expansion foams will generate more foam from less foam concentrate and thus be more effective ?

So the high expansion foam is very light and low expansion foam is comparatively heavier.

If we use high expansion foam for deck fires, the foam will fly with the wind and will not be able to extinguish the fire.

For this reason, for deck fires low expansion foam is used. On tankers, it will always be low expansion foam for fires of the cargo area.

High expansion foams are used for compartments such as holds and even machinery spaces where the space need to be filled with foam for fire fighting.

Functioning of Fixed foam system

Below is the basic line diagram of a typical fixed foam system on ships.

The foam pump takes the foam concentrate from foam tank and injects it in desired ratio into the water. The proportioner controls the quantity of foam solution to inject.

The common type of proportioner is of ejector type. The more the fire line pressure, more foam it will inject. Ship staff are not supposed to touch the proportioner.

When the foam solution reaches foam nozzle on deck, the air is injected into the foam solution to create the fire fighting foam.

The foam so generated creates a layer over the fire and cuts the oxygen supply, the process called smothering to extinguish the fire.

Maintenance required on fixed foam system

There are many components of the fixed foam system such as

• Foam line
• Foam monitor
• Foam isolation valves
• Fire pumps
• foam concentrate (foam solution)
• Foam pump
• foam proportioner

Each one of these need to work as desired. We, the ship staff need to make sure that each one of these are in perfect condition. The only way to ensure that is by testing of all element of foam

i) Testing of foam line, foam monitor and foam isolation valves

If the foam line is leaking, or the foam monitors cannot be turn around to aim the foam at the fire, we would not be able to use the foam system.

Every year the foam line need to be pressure tested at least to the maximum working pressure. We must check the SMS manuals of the ship for any special testing requirements from the company.

The testing procedure would be

• Close all the valves of the fire line and foam line
• Open the foam monitor on the forward most part of the ship
• Start the fire pump at maximum pressure
• Slowly close the foam-monitor that was kept open
• Check for any leakage

Apart from checking the foam line leakage, we also need to check if any foam monitor valve is leaking. For this we just need to check that no foam monitor is leaking when the foam line is pressurised.

If we spot a leaking foam monitor, we must first check if the foam valve is tightly shut. If it is still leaking, we should overhaul the foam valve.

Remember, foam system is a critical equipment. And if we plan to remove the valve for overhaul, we must carry out risk assessment as for the period of the overhaul, the foam system would not be available for use. The company may also require the ship to take their approval before proceeding with this work.

We also need to test if the foam isolation valves are holding.

To test the foam isolation valves

• Keep the forward most foam monitor open
• Close the foam isolation valve one by one and check if the water from the foam monitor stops completely.

ii) Foam pump

We test the foam pump during the fire drill involving fire on deck. The foam pump is run on recirculation. We must make sure that the part of the foam line involved during re-circulation is effectively drained and empty after testing.

iii) Fire pump

Fire pump is an important part of the foam system. It delivers the foam solution to the foam monitors. While testing the fire pumps for foam system, we run the fire pump at full pressure.

We then open the two foam monitors and directs the jets overboard. The jets from these two should be able to cross each other.

iv) Foam concentrate

The main element from which the foam is generated is Foam concentrate stored in the foam tank. We have to check two things for foam concentrate

• Quantity of the foam concentrate
• Quality of the foam concentrate

For the vessels fitted with inert gas system, there need to sufficient foam concentrate for running for 20 minutes at maximum flow rate.

For vessels not fitted with inert gas system, there should be sufficent quanitity of foam concentrate for running for 30 minutes at maximum flow rate of the fire system.

The required quantity is usually marked on the foam tank gauge. We must ensure that this quantity is never below the mark.

With regard to quality of the foam, there is only one way we can know. By analysis of sample of foam

Sample analysis of foam concentrate

SOLAS requires the foam sample to be tested after 3 years from the date it was placed onboard and there after every year.

Various tests are carried out on the foam sample to ensure that the foam is fit for the purpose it is supposed to do. The tests include

Sedimentation Test: Sediments should be less than 0.25%

pH value test: The pH of the foam concentrate should not be less than 6 and not more than 9.5 at 20 Deg C

Drainage time test

Chemical stability test for Alcohol resistant foam: 

The alcohol resistant foams are different from other type of foams. Water content from normal foam will dissolve in the solvent and so these forms are not suitable for solvents. Additives in the alcohol resistant foam form a membrane that separates the solvent and foam which avoids the breaking up of the foam blanket.

SOLAS REGULATION FOR FIXED DECK FIRE FOAM IN SHIP :

 1)The arrangements for providing foam shall be capable of delivering foam to the entire cargo tanks deck area as well as into any cargo tank, the deck of which has been ruptured. 

(2) The deck foam system shall be capable of simple and rapid operation. The main control station for the system shall be suitable located outside the cargo area adjacent to the accommodation paces and readily accessible and operable in the event of fire in the areas protected. 

(3) The rate of supply of foam solution (that is, the mixture of foam concentrate and water before expansion) shall be not less than the following whichever is the greatest: 

1. 0.6 litre per minute per square metre of cargo tanks deck area, where cargo tanks deck area means the maximum breadth of the ship times the total longitudinal extent of the cargo tank spaces. 
2. 6 litre per minute per square metre of the horizontal sectional area of the single tank having the largest such area; or
3. 6 litre per minute per square metre of the area protected by the largest monitor, such area being entirely forward of the monitor, but not less than 1, 250 litres per minute. 

(4) Sufficient foam concentrate shall be supplied to ensure atleast 20 minutes of foam generation in ship fitted with an inert gas system complying with solas to these Regulations or 30 minutes of foamgeneration in ships not fitted with an inert gas by system when using the solution rates stipulated in paragraphgraph  (3) . 

(5) Foam from the fixed system shall be supplied by means of monitors and foam applicators.  At least 50 per cent of the foam solution rate required in sub-paragraphs (a) and (b) of paragraph (3)  shall be delivered from each monitor.  On tankers of less than 4,000 tonnes deadweight, applicators may be substituted for an installation of monitors.  In such a case the capacity of each applicator shall be at least 25 per cent of the foam solution rate required in sub-paragraphgraph  (a) or (b) of paragraph (3). 

(6) (a) The number and position of monitors shall be such as to comply with paragraph  (1).  The capacity of any monitor shall be at least 3 litres per minute of foam solution per square metre or deck area protected by that monitor, such area being entirely forward of the monitor.  such capacity shall be not less than 1,250 litres per minute. 

(b) The distance from the monitor to the farthest extremely of the protected area forward of that monitor shall not be more than 75 per cent of the monitor throw in still air conditions. 

(7) A monitor and hose connection for a foam applicator shall be situated both port and starboard at the front of the poop or accommodation spaces facing the cargo tanks deck.  On tankers of a dead weight of less than 4,000 tonnes not fitted with monitors a hose connection for a foam applicator shall be situated both port and starboard at the front of the poop or accommodation spaces facing the cargo tanks deck. 

(8) The capacity of any applicator shall be not less than 400 litres per minute and the applicator throw in still air conditions shall be not less than 15 metres.  The number of foam applicators provided in accordance with the requirements of paragraphgraph  (5)   shall be not less than four.  The number and disposition of foam main outlets shall be such that foam from at least two applicators can be directed on to any part of the cargo tank deck area. 

(9) Valves shall be provided in the foam main, and in the fire main when this is an integral part of the deck foam system, immediately forward of any monitor position to isolate damaged sections of those mains. 

(10) Operation of a deck foam system at its required output shall permit the simultaneous use of the minimum required number of jets of water at the required pressure from the fire main. 

System Description

The form pump take suction from foam concentrate foam tank and inject it in desired ratio into the water. The proportional controls the quantity of FOAM solution to inject. The common type of proportional is of ejector type the more the fire line pressure,more form solution  will inject. Ship staff are not supposed to touch the proportionar when the form solution reaches form nozzle or foam monitor the air is injected into the foam solution to create the fire fighting foam. The foam so generated creates a layer over the fire and cuts the oxygen supplyto extinguish the fire. If a fire breaks out in enclosed area or vessel, we depend on an extinguishing system that deploys quickly, effective and safe for personal. This system is cost effective and safe for the crew and environment fast and effective solution for machinery spaces fire with filling rate of 1.8 metre per minute the system can be installed as a total flooding system for the entire machinery room or for individual compartment .Quick activation of the system, minimum fire and heat damage to equipment and structure form is not harmful and the cooling effect hinders the fire from ignition after it is extinguish use no hazardous decomposition product that would cause damage . It is formed expansion ratio of 1 :666 at nominal pressure of 6 by using inside air. It uses a synthetic foam concentrate. The system consists of foam generator ,foam Storage tank, foam concentrate ,foam Storage tank at atmospheric pressure, foam pump, form proportionate, distribution pipe made up of galvanized steel ,strainer, valve ,test and blow through lines ,power and control system for optimal effectiveness it is critical that the foam concentrate is mixed with water in the correct proportion throughout the fire fighting operation . Foam generator expand the foam mixture with the use of air drawn from the protected space. The system can be manually released released from the form room by directly operating the valves and Pump it can also be operated by centrally located control cabinet for operational flexibility.

 This can  can act at an emergency during main power source failure.

 Solas regulation for fixed foam fire fighting system

-rate of 1 metre  per minute 

-500 metre cube and above 2000 GRT and above should have a fixed fire fighting system.

-Quantity of form for forming liquid is equal to 5 times volume of largest space to be protected.

-Foam concentrate for 30 minutes.

- A system should be approved by administration 

-System shall be capable of manual activation automatic interlock is not permitted unless appropriate interlocks are provided.

-System away from protected space.

-Operating instruction for system shall be displaced at main as well as local control station.

-The foam generator shall be located at the place where adequate fresh air supply can be arranged.

-The arrangements shall be provided for the crew to safely check the quantity of foam concentration.

-Supplied with main and emergency power source.

-Pipeline should not interfere with the access to the installation of machinery for routine maintenance.

 -The foam generator room Shall be ventilated to protect against overpressure and shall be heated to avoid the freezing.

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