On board, we use foam as firefighting agent in different type like portable, semi-portable and fixed. In this blog, we will discuss each about fixed fire fighting system, working, components, SOLAS regulations, types, properties, and some important terminology.
It is a composition of water and foam making agents, which extinguishes the fire. The complete foam solution is generated by aerating device, the foam bubbles are created because of introduction air to foam solution.
Properties of the Foam
- Knockdown speed and flow – It is the ability of foam that how fast foam is flowing on the burning fluid surface and obstruct its propagation. Therefore higher the knockdown speed and flow better will be the foam for fire extinguishing.
- Cohesive Properties – Due to this property the foam should be stick together to establish and maintain a vapour tight blanket over burning substance.
- Heat Resistance– Effect to resist the heat from any remaining fire from the liquids flammable vapours. This property will help to prevent re-ignition of the fire.
- Vapour Suppression– Capability of foam to suppress the flammable vapours to break the fire triangle, which helps to extinguish the fire.
- Alcohol Resistance– If we are using the foam on alcohol-based cargo then that foam must have alcohol resistance property. Otherwise, alcohol will destroy the foam blanket by dissolving the water. Solvent-like alcohols are miscible in water.
- Light Enough– High expansion foam should be light enough to flow on fuel surface. Whereas low expansion should be light enough to flow of fuel surface as well as heavy enough to resist the wind.
Following characteristic of foam helps to extinguish the fire-
- Separating effect – Foam is able to separate the combustible material/fuel from the fire, which gives starving effect and extinguish the fire.
- Cooling effect– Foam contains water molecules which give cooling effect too.
- Cover effect – Foam is having the ability to form a blanket, and it flows with fuel. In this ways, foam gives full cover all the time, which helps to separate them from the atmosphere.
- Repression effect – Foam represses the oxygen and other flammable gases necessary to extinguish the fire.
- Insulation effect– Foam insulates the flammable materials which will not allow catching the fire.
Types of foam
- Chemical foam – These foams are produced by chemical reactions of two chemical one is an acid (aluminium sulphate) and second is alkali (sodium bicarbonate). The reaction realises energy which helps to form the foam. In the foam bubbles, carbon dioxide gas is present which is generated during the chemical reaction. For storage of these chemicals, we need two separate tanks or any other similar arrangement, which requires more space for this system. And also the time required for the formation of foam is more, because of the reaction time between both chemicals taken by this system is more.
- Mechanical foam– These foam are formed by adding foam agents into water and bubbles are created by turbulent mixing of air in foam solution. There are different types of mechanical foams.
- Protein foam – This foam is formed by the hydrolysis of waste protein material, such as protein-rich animal waste and vegetable waste. It is used on hydrocarbon fuels only.
- Fluoroprotein foam – This is formed by adding special fluorochemical surfactants with protein foam.
Filmforming fluoroproteinfoam (FFFP) – This is formed by adding special fluorochemical surfactants with protein foam which release a film on the surface.
- Aqueous film forming foam (AFFF) – This is the combination of fluorochemical surfactants and synthetic foaming agents. As its property of film forming, it is commonly used on board ship especially on a tanker ship.
- Alcohol resistance aqueous film forming foam – This is AFFF having properties of alcohol resistance.
- Synthetic foam– this is made up of alkyl sulfonates and it is more readily than the proteins and required less amount of water.
Nowadays the use of chemical foam is very limited, because of its inability to discharge fast. The discharge rate of the foam from the chemical type extinguisher depends on how fast the foam will be generated in the extinguisher.
What is the expansion ratio?
The ratio of the volume of the foam agent at the very initial stage to the actual foam volume formed after mixing with water and air in the final stage. For example, if a small quantity of foam concentrate is allowed to mix with the water forming a solution of the liter, and after mixing with air the final solution formed is having a volume of 1000 liters. Then the expansion ratio of this foam is rated as 1000 to 1 i.e. 1000:1. Normally the water content of the foam water mixture should be 92% to 96% of the solution, rest will be foam concentrate. This ratio of mixing will be adjusted by proportioner. The above-given example is of high expansion foam. Onboard we use only high and low expansion foam. But on the base of expansion ratio, there are three types of foam –
- Low expansion foam – These foam solutions are having expansion ratio less than 12:1. these are used for cargo deck area.
- Mid expansion foam – These foam solutions are having an expansion ratio of more than 20:1, but less than 100:1
- High expansion foam – These foam solutions are having expansion ratio above 100:1. They are light in weight than other mid and low expansion foam, used only in machinery space/engine room.
Why we use low expansion foam on deck and high expansion foam in the engine room?
Low expansion foam is having a more weight to volume ratio as compared to high expansion foam. If we use high expansion on deck, then wind effect will blow away the foam. The low expansion foam having sufficient weight to counter the wind force effect. So, it is easier for low expansion foam to form a blanket over fire properly. In the engine room, wind effect is not present only we need to suppress the flammable gases and to give a cooling effect in the large volume of the engine room. So high expansion foam is good to cover more space in a short time.
Advantages of foam firefighting
- Effective smothering and cooling effects
- Prevent flammable vapours to form and spread.
- It can we used on class A, B, C
- Effective in forming a blanket on the oil spill
- Foam system uses water economically
- It can be used with sea water and fresh water
- The system doesn’t take much space
- It helps to prevent re-ignition of fuel
SOLAS requirement of Low Expansion foam firefighting system
- Foam system should be approved by the administration
- Foam monitors should have the capacity to discharge 3litres/m2/minute.
- The system should contain five times the volume the of largest space
- Expansion ratio should not exceed 1000:1
- The main control station should be located away from the cargo area, adjacent to accommodation space.
- The system shall be capable to discharge foam, in no more than 5 minutes, the quantity should be sufficient to form a foam blanket over the largest single area over which oil fuel is liable to spread.
- The system shall be capable to supply foam not less than 20 minutes on tanker fitted with inert gas system and not less than 30 minutes on tankers not fitted with the inert gas system.
- The rate of supply of foam shall not be less than the greatest of following
- 0.6 l/min per square meter of cargo tanks deck area, where cargo tanks deck area means the maximum breadth of the ship multiplied by the total longitudinal extent of the cargo tank spaces
- 6 l/min per square meter of the horizontal sectional area of the single tank having the largest such area; or
- 3 l/min per square meter of the area protected by the largest monitor, such area being entirely forward of the monitor, but in no case should the output of any monitor be less than 1,250 l/min.
- The capacity of an applicator shall not be less than 400l/minute and should capable of through foam not less than 15 meters in still air condition.
SOLAS regulation for High Expansion Foam
- The system shall be approved by the administration.
- The system shall be capable of manual activation and shall be designed to produce foam at the required rate within 1 minute of release. Automatic activation is not permitted unless appropriate interlocks are provided.
- The system and control station shall be located away from protected space.
- The quantity of foam concentration shall be sufficient to produce the foam volume equal to at least five times the volume of largest protected space(E/R), at the nominal expansion ratio, or enough for 30 minutes of full operation for the largest protected space, whichever is greater.
- The system should be capable of rapid discharging foam @ at least 1 meter in depth per minute
- The operating instruction for the system shall be displayed at main as well as local control stations.
- If an IC engine is used as a prime mover for seawater pump for the system then the fuel tank of that engine shall contain sufficient fuel to run the pump on full load for at least 3 hours and reserves of fuel shall be available outside the machinery space of category A to enable to run the pump on full load for additional 15 hours.
- The foam generators shall be located at the place where adequate fresh air supply can be arranged.
- The arrangement shall be provided for the crew to safely check the quantity of foam concentration.
- The arrangement of foam generators and piping of the foam system in the protected space shall not interfere with the access to the installed machinery for routine maintenance activities.
- The system shall be supplied main as well as the emergency source of power.
- The foam generator room shall be ventilated to protect against overpressure, and shall be heated to avoid the freezing.
Working of Foam Fire Fighting System
The foam firefighting system generally consist the following components –
- Foam tank– It is used to store the foam concentrate. The tank is fitted with the level gauge to monitor the foam level in the tank. Regular inspection of tank and foam concentrate should be carried out.
- Foam pump– A centrifugal pump is fitted in the system which pumps the foam making agent from foam tank too the water line.
- Proportioner– It is a device fitted in the system to control the amount of foam concentrate mixing with water to form a foam solution.
- Fire pump – Used to supply water in the system. No separate pump is required, it can be a fire pump or any other sea water pump.
- Foam monitors– It is used to discharge the foam and water solution. It also facilitates the mixing for air with the foam-water solution
- Foam hose & foam nozzle- Used with foam monitor to extinguish the fire as early as possible.
- Isolation valves and non-return valves- These fitted to isolate the non-desired line and to prevent the backflow. On deck, many isolation valves are fitted.
Woking of the foam fire fighting system–
Foam concentrate is stored in a foam tank. The foam pump takes suction from the tank and injects it in the water line. This foam concentrate quantity is controlled by the device proportioner. The water in the line comes from the fire pump. As shown in the diagram a water line is coming from the fire pump and another line from foam pump connecting at proportioner. The amount of foam concentrate required is added to the water with proportioner and remaining foam goes back to foam tank. Sometimes a relief valve is also provided in the return line, it will solely depend on the type of proportioner in use.
This foam solution is carried through pipes(always painted in yellow) to the desired location. A foam monitor or nozzle is provided at end of it. The function of the monitor and nozzle is to suck air from the atmosphere and mix it with foam solution. It also works on venturi effect. The high-pressure foam solution when passes through the monitor it creates a low pressure and air will rush inside through provided holes. Because of the shape of the foam monitor(eductor shape -big opening at the outlet), the foam solution and air have turbulence in the flow. Therefore, the intermixing of foam solution and the air is very good. The outcoming foam should always be directed at the base of the fire, or at the bulkhead if nearby.
Working of proportioner –
There are countless types of proportioner used for foam mixing with water, but all of these are the varient of these three basic types of proportioner. The sole aim of the proportioner is to mixing an optimum quantity of foam concentrate with the quantity of water provided. These types include:
- Educator foam proportioner
- Balanced pressure foam proportioner
- Turbinator foam proportioner
1. Educator type
This is an old type proportioner which works on venturi effect. In this proportioner, the educator is provided with sea water as driving water and foam concentrate as driven water. The amount of seawater passing through the educator will create a pressure drop in it. Because of this pressure drop, the foam concentrate will rush in. And the amount of foam concentrate will be directly proportional to the pressure created by sea water. Therefore the quantity of foam concentrate mixing with the seawater is dependent on seawater quantity. The final mixing ratio of both will be because of the eductor design. Normally 95% will be the sea water and remaining will be the foam concentrate in solution.
Although this system doesn’t require a foam pump to operate, it is provided to recirculate foam concentrate periodically. This system is not being used on the ship
2. Balance-pressure type
This is a commonly used type of proportioner on board ship. This proportioner looks like a gate valve, but it is not. The amount of the foam concentrate will depend on the sea water line pressure. One small spring loaded valve is provided in the foam concentrate line. The opening of the valve is controlled by sea water line pressure.
Here two system are shown, in the first system a flap is provided, which restrict the path of sea water. This flap is connected to the foam valve and work opposite to the spring of the valve.
In another system, the diaphragm valve is provided, it will control the valve opening in proportion to the sea water pressure through a pilot line provided. Higher the pressure of seawater more flow of foam is allowed to pass through that valve.
This a very new type of proportioner, only employed in big shore-based plants. In this, a water pump is driven by the seawater(or fresh water, whichever is in use). This pump will work as a prime mover for a small pump to drive foam or some time same water pump vacuum can be used to drive the foam concentrate. As the pump speed will be depended on the volume of the water passing through it, so, the amount of foam concentrate mixing with water will also depend on the same.
Note-Proportioner must be tested by outside agency every five years. Onboard same to be kept in record. It allowed the variation of +30% to -10% from the designed value.
Precautions before using foam system
- Permission to be taken by the master and the system to be operated by a competent engineer.
- Headcount to be taken and ensure all persons are outside from the protected space.
- Nearby vessel and port authority to be informed.
- Make sure the system is in good working condition.
- Check the level in the foam tank.
- Do not run the foam pump dry.
- Open isolation valves and one of the foam monitor valve to avoid excess pressure in the line.
- While using low expansion foam on deck
winfeffect to be considere
Procedure to release the foam to fight the fire on the deck
- Open the sea suction valve and start the fire pump or sea water pump.
- Open foam monitor stop valves and isolation valves as required, and fire water supply valve.
- Open foam liquid non-return valve.
- Start foam liquid pump. Check for rotation and pressure is being generated. If the pump fails to generate pressure, shut down the pump and prime.
- Check foam liquid pressure
- Open foam liquid proportioner valve.
- Operate foam monitors as required to bring the fire under control.
- Do not operate foam liquid pump against a closed valve for more than 3 minutes unless a continuous bypass, returning the foam liquid to the tank, is incorporated.
- After use, close foam liquid non-return valve and shut down foam liquid pump.
- Flush the system with clean water until water issues from foam monitor. This can be done by opening flush line.
- Close the sea water suction valve and shut down firewater pump.
- Return all valves to their contents and replenish as necessary.
- If the foam liquid has been emptied during operation, the tank should be thoroughly flushed out and drained before refilling.
Procedure to enter in the protected area after using foam as firefighting agent
- Do not enter into the protected area immediately after extinguishing. Allow the area to cool down, high temperature may cause injury.
- Use proper breathing apparatus to enter into space. Hazardous and toxic gases may present into space.
- Entry shall be made by an authorised and competent person. An authorised person should be standby at the entrance to communicate between the person inside and to the control station.
- Use only explosion proof light, do not use any naked light or burning light or cigarette.
- Use the personal gas meter and periodically check the toxic gases into space.
- Use fresh water mist to clean the room. The electrical machinery to be cleaned by cloth and use hot air to remove the moisture.
- Drain the foam line with the compressed air.
- Check the line and nozzles for any damage. If anything found maintenance to be done as soon as possible.
- Put all the valve of the system into normal position. Check the foam level into foam tank, if required same to be filled as soon as possible.
Maintenance on fixed foam fire fighting system
- Check that all valves have free movement and position, normally open or closed to be checked.
- Check the level of foam liquid in the main foam liquid storage tank
- Check for free movement of foam monitors and secure in parked position.
- Check electric supply to foam pump. Do not run the pump dry.
- Start the fire pump. Open the foam monitor water stop valve and run for few minutes ensuring that there is no trace of foam liquid in the system and the monitors are performing satisfactorily. After check put it in normal condition.
- Run the system actually from one foam monitor and ensure that sufficient foam is producing and the system is working satisfactorily.
- Check the level in foam tank and replenish as necessary.
- Check all foam liquid strainer and clean as necessary.
- Greasing of motor pump bearing.
- Take the sample of foam liquid from the storage tank and send to manufacturer for analysis.
- Foam line must be tested yearly at maximum working pressure. For pressure test, we have to follow the SMS checklist. Same to be recorded.
- During the pressure test, we have to also check the leak and holding of isolation valves.
- Check that dampers are closing or not.
- Check the automatic fuel shut off. If we are using for engine room fire.
- Blow dry air or nitrogen through the piping.
- Proportioner to be checked and verified by outside agency and certificate to be issued.
- Check all the nozzles and make sure they are clear.
- Flush the piping with fresh water, drain and purge with the air.
Procedure to take foam sample
- Circulate the foam contents for the 5-7 minute before taking the sample.
- The sample should be taken from the sampling point. Flush that to remove any accumulation or sludge.
- If it is not possible to circulate then take the sample from 3 point top, middle and bottom of the tank.
- If not possible to take from the above three-point due to the construction of the tank or any other reason. Then take from two-point top and bottom of the tank.
- The sample must be at least 500 ml in volume.
- The sample should be packed tightly sealed container made of polyethene.
- Sample container must be labelled (do not use gummed labels) with a waterproof pen.
- The label of the sample must contain the name of the company, vessel, type of concentration and source of the sample. We have to mention other information as per request of the analysis.
Foam sample test
- Sedimentation test – Sediments comprises of microscopic particles, more percentage of sediments are the result of equipment corrosion that the foam has come into contact with during the sampling procedure. The sediments should be less than 0.25%.
- pH value test – its shows the acidic or basic nature of the sample. pH of the foam concentration should be between 6 to 9.5 at 20°C. This test is important to prevent the corrosion.
- Drainage test –
- Alcohol tolerance test – It shows the alcohol resistance properties of the foam.
- Small fire test – In this test we actually perform a real fire test. Means with the sample of foam we generate foam and applying that on a small fire just to verify that it’s actually working satisfactorily.
- Certificate of type approval
- Foam lab testing report