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Foam portable extinguishers -fire protection system for cargo ship

Fire protection on ships is provided by detection and fire-fighting equipment together with structural features which are intended to contain an outbreak of fire and the employment when required of non-combustible materials to prevent its spread.

Chemical foam extinguisher

The outer casing of the portable (chemical) foam extinguisher (Figure 14.31) is similar in construction to the soda-acid appliance and is required to withstand the same initial test pressure of 25 bar and is retested at 21 bars every four years.

This extinguisher has a long inner container of polythene suspended from the neck ring and filled with aluminium sulphate solution. The outer container is filled to a marked level with sodium bicarbonate solution. A lead disc sits on top of the inner container and acts as a stopper. By inverting the extinguisher and shaking it, the disc is dislodged and the two solutions mix with the reaction:
Al2(SO4)3 + 6NaHCO3 = 2Al(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 has to be inverted for operation, no internal pipe is fitted. When being recharged the cap seal should be examined and the pressure relief holes in the rim checked. The chemical foam extinguisher may be slow acting in cold conditions and unreliable if the chemical has deteriorated due to heat.

Portable foam extinguisher
Figure : Portable foam extinguisher
Figure 14.31
A Steel container D Lead sealing weight F Removable nozzle B Neck ring E Gunmetal top cap G Alkali level indicator C Inner acid container

Mechanical foam extinguisher

The alternative type of portable (mechanical) foam extinguisher shown in Figure 14.32 is preferred to the chemical foam type, described previously. The appliance is filled with water and contains an inner container with a small metal bottle of liquid carbon dioxide, surrounded by a plastic bag of foam making compound.

To operate this extinguisher it is necessary to strike the plunger on the cap sharply, thus piercing the seal of the CO2 bottle. The gas then ruptures the plastic bag of foam compound and ejects the water and foam compound through a special nozzle which agitates the mixture and creates a mechanical foam. In this type of extinguisher the ratio of foam to liquid is about 8:1. The extinguisher has an internal pipe and is operated in the upright position.

Mechanical foam extinguisher
Figure : Mechanical foam extinguisher
The first line of defence against fire in any area of the ship, is the portable fire extinguisher. Some common portable extinguishers that have been used at sea are described.
  1. Soda-acid extinguisher (discharges water)

  2. The main body of the Soda acid extinguisher contains sodium bicarbonate, an alkaline solution. The extinguisher must be kept upright when in use. The operator strikes the pin at the top to break the acid phial so that acid and alkali mix, to form carbon dioxide which forces the water (with the chemical remains) out of the discharge. The device must be held upright in use. .....more

  3. Foam portable extinguisher

  4. Mechanical Foam extinguisher is filled with water and contains an inner container with a small metal bottle of liquid carbon dioxide, surrounded by a plastic bag of foam making compound. .....more

  5. CO2 portable fire extinguisher

  6. While carbon dioxide is used in some extinguishers as an inert propellant the gas is also used extensively as a blanketing agent. The carbon dioxide is in liquid form and is at a pressure of 6 bar at 20 deg C necessitating a strong container. This type of extinguisher can only be recharged ashore. .....more

  7. Dry powder portable extinguisher

  8. This type of extinguisher contains sodium bicarbonate powder with a water proofing agent such as magnesium stearate to prevent caking. The container shown holds a cartridge containing liquid carbon dioxide. On piercing its seal with the plunger pin, the gas is delivered through a tube to the bottom of the casing where it entrains the dry powder and carries it up through the discharge tube. .....more

    Portable halon extinguisher The use of halon in portable extinguishers should be discontinued when suitable alternatives are available because of the high ozone depletion potential.

Summarized below more fire protection equipments & guideline:
  1. Fire main system & related mechanism

  2. The fire main extends to the full length of the ship and from the machinery spaces to the highest levels. Hydrants served by the main, are situated so that with suitable hoses any area on the ship can be reached. .....more

  3. CO2 fire extinguishing installation

  4. Fire extinguishing installations employing CO2 stored under pressure at ambient temperature are extensively used to protect ships' cargo compartments, boiler rooms and machinery spaces. When released the CO2 is distributed throughout the compartment, so diminishing the relative oxygen content and rendering the atmosphere inert. ...... more

  5. Fire fighting equipments

  6. Two independently powered pumps must be provided in all cargo ships of 1000 tons gross and over and in passenger ships of less than 4000 tons gross. Larger passenger vessels and passenger ferries must have three such pumps. The pumps are fitted with non-return valves if they are of the centrifugal type, to prevent loss of water back through open valves when not running. ..... more

  7. Details of fire detectors

  8. A variety of devices are available for detecting fire in unmanned machinery spaces but each has an ability to detect basically only one aspect. Thus, smoke detectors based on the ionization chamber are able to recognize combustion products but will not register radiation from a flame or heat. .....more

  9. Machinery space fire & use of Walter Kidde CO2 system

  10. Walter Kidde CO2 system employs pilot CO2 cylinders to open the distribution system main stop valve and subsequently the valves on the individual CO2 cylinders. .....more

  11. Fire protection system for cargo holds

  12. Holds for general cargo, have been protected against fire by fixed installations which deliver inert gas from an inert gas generator based on combustion of fuel (similar to the system available for inerting oil tankers) and halon systems. .....more

  13. Low pressure CO2 storage

  14. In some installations, the CO2 is stored in low pressure refrigerated tanks. The cylindrical storage vessels 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. ..... more

  15. Halon system

  16. Halon 1301 has the chemical formula CF3 Br being known as bromo-trifluoromethane. It is a colourless, odourless gas with a density five times that of air and extinguishes fire by breaking the combustion chain reaction. .....more

  17. Multi-spray system for the machinery spaces

  18. 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. .....more

  19. Automatic sprinkler system

  20. A network of sprinkler heads is arranged throughout the spaces to be protected. Each sprinkler head is normally kept closed by a quartzoid bulb which is almost filled with a liquid having a high expansion ratio. .....more

  21. Details various portable extinguishers & how to use ?

  22. The first line of defence against fire in any area of the ship, is the portable fire extinguisher. Some common portable extinguishers that have been used at sea are described. .....more

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