What is the principle of the fire extinguisher？

A fire extinguisher is a pressurised vessel designed to attack a fire in the early stage. Pressure inside the extinguisher is used to expel the extinguishant, which will either smother, cool or chemically interfere with the fire; or fight the fire by combining two or more of these effects.

WATER, FOAM & DRY POWDER Extinguishers containing water, foam or dry powder may be similar in appearance, except that they will be clearly labelled and colour coded so that the content may be easily identified, and they all operate on the same principal. In each case the medium is stored in a welded container. When the valve is opened C02 gas exerts a downward pressure on the water, foam or dry powder, forcing it up a syphon tube and out through the delivery hose. The discharge will be controlled by either squeezing and releasing the operating head valve or by a control lever at the end of the discharge hose.

CARBON DIOXIDE (C02)

Where the extinguishing medium is itself C02 the gas is stored as a liquid under pressure. Because of the pressures involved C02 extinguishers are not welded containers but solid draw. Upon discharge the liquid expands into CO2 gas.

STORED PRESSURE OR CARTRIDGE OPERATED The C02 used to expel the medium may either be applying permanent pressure within the extinguisher or stored in a small cartridge found inside the extinguisher and connected to the operating head. In the latter case when the operating head is depressed C02 from the cartridge fills the main body of the extinguisher in order to expel the medium.

SITING OF EXTlNGUISHER LOCATION

Normally, extinguishers should be located in conspicuous positions on brackets or stands where they will be readily seen by persons following an escape route. The carrying handle of larger, heavier extinguishers should be about 1 m from the deck but smaller extinguishers handles should be about 1.5m from the deck. Siting positions near to room exits, alleyways, stairways, lobbies and landings are most suitable. Attention should be drawn to the position by photoluminescent signs. The extinguishers, type and size, should be shown on the vessels Fire Plan, or, in the case of smaller craft, on some other suitably arranged diagram.

Extinguishers should be available for immediate use at all times. The number of extinguishers required will vary depending on the type of vessel and the risk.

Typically

on passenger vessels and ferries -

below the bulkhead deck, and in every vertical zone, there shall be at least two extinguishers available in every accommodation space, service space and control station.

In enclosed accommodation spaces, service spaces and control stations above the bulkhead deck there should be at least one extinguisher on each side of the ship, on cargo vessels and tankers -

one extinguisher should be provided in each of the spaces given above.

Additionally there will be a minimum number of extinguishers required and portable and semi- portable extinguishers are also required in machinery spaces, ro-ro spaces and ro-ro space accesses.

Where possible it is advisable to site extinguishers at similar positions on each deck. It is not advisable to place extinguishers in positions in rooms or alleyways away from exit points unless they are necessary to cover a particular hazard.

Extinguishers should not be placed in concealed positions, behind doors, in cupboards or deep recesses, unless their position is indicated by a suitable photoluminescent sign. They should not be in positions where they might cause obstruction to exit routes or be damaged by general movement around the vessel, or be close to heating appliances.

AVOIDANCE OF EXPOSURE AND CORROSION

Extinguishers should not be exposed to storage temperatures outside of the designed range. Neither should they, unless specially treated by the manufacturer or protected by a specific housing, be located in places where they may be exposed to a corrosive atmosphere or corrosive fluids. Extinguishers which stand on the deck where dampness may cause corrosion should be of a suitable type and carefully monitored as to their condition.

The most appropriate extinguisher should be found near any risk, but this may not always be the case, especially where there is more than one risk in the same area. For instance, in a Control Room there may be hydraulics, computers and other electrical equipment, papers and books. If the wrong type of extinguisher is used on a fire the already serious situation may be made considerably worse. Using a water extinguisher on a chip-pan fire could result in a contained, controllable situation becoming a catastrophe as the effect of directing water into burning hot fat is to cause the fire to spread. It is important that every crew member is familiar with the advantages and limitations of each fire extinguishing medium.

CHOOSING THE CORRECT EXTINGUISHER

The most appropriate extinguisher should be found near any risk, but this may not always be the case, especially where there is more than one risk in the same area. For instance, in a Control Room there may be hydraulics, computers and other electrical equipment, papers and books. If the wrong type of extinguisher is used on a fire the already serious situation may be made considerably worse. Using a water extinguisher on a chip-pan fire could result in a contained, controllable situation becoming a catastrophe as the effect of directing water into burning hot fat is to cause the fire to spread. It is important that every crew member is familiar with the advantages and limitations of each fire extinguishing medium.

WATER

Suitable for use on wood, paper, plastics and textiles (Class A fires)

DO NOT USE on fires involving liquid (oils, paints, fats, cleaning fluids, etc.)

DO NOT USE on fires where there is live electricity in the vicinity

FOAM

Suitable for use on liquid spills and contained liquid fires of oils, paints, cleaning fluids, etc. and fires involving liquifiable solids such as fats and waxes (Class B fires)

DO NOT USE on fires where there is live electricity in the vicinity

DRY POWDER

The type of powder known as BC Powder is suitable for use liquids and liquifiable solids as described under FOAM above (Class B fires). BC Powder may also, with the correct technique, be used to extinguish a high pressure gas flame (Class C fires). Additionally ABC Powder or Multi-Purpose Powder may be used against carbonaceous fires (Class A fires).

Dry Powder gives a fast flame knock-down, and may be used on fires involving live electricalequipment. However, it may not be effective against a deep seated fire. AVOID inhalation of powder.

CARBON DIOXIDE

Suitable for use on Class A & B fires and for Class C fires when in a liquid state (e.g. liquid gas leak such as methane, propane, butane, acetylene or hydrogen)

Safe for use on fires involving electricity.

May not be effective when used outside, especially in a breeze

DAGGER Hold only the insulated parts of the discharge hose and horn. With the expansion and evaporation of the C02 there are cooling processes and a danger of frost burn if the discharge horn is not correctly held.

DANGER If using a C02 extinguisher in an explosive atmosphere stand it on the ground to ensure any electrostatic change is dissipated.

DO NOT US：- without a discharge horn as the discharge will then entrain air and cause an increase in the intensity of the fire.

DANGER Do not remain in the area after the discharge as C〇2 is asphyxiating.

COLOUR

FIRE EXTINGUISHER COLOUR CODING Fire extinguishers may be colour coded to indicate the extinguishing medium they contain. Older extinguishers in UK registered vessels may have the entire body of the extinguisher appropriately coloured; more recent extinguishers will be red

with a block of colour placed above the operating instructions. Some vessels may have extinguishers any colour coding: in this case

it is necessary to read the instructions to determine the extinguisher contents.

In addition to fire extinguishers normally having some form of colour coding to indicate their contents, modern fire extinguishers will also bear graphic symbols to show the types of fire for which the contents are suitable. The symbol for electrical hazard will be shown on those extinguishers whose contents are safe to use on fires involving all types of electrical equipment.

 EXTERNAL INSPECTION

♦Is the safety pin in place, and operating freely?

♦Examine the exterior, including the base for signs of corrosion.

Ensure that all instructions are legible and in appropriate languages.

If the unit is of the stored pressure type and has a gauge, is it showing an acceptable reading?

♦Examine the hose and/ or horn and their securing clips for signs of cracking or damage.

♦Inspect the bracket for damage and ensure that it is securely attached.

♦Are the appropriate signs and instructions displayed adjacent to the extinguisher?

♦Stored pressure units should be weighed and this compared against the weight stamped into the extinguisher body (solid drawn cylinders) or marked on the service label. If there has been a loss of more than 10% of the content weight the cylinder should be recharged by a competent person. Note: some manufacturers recommend that only authorised service engineers recharge their stored pressure extinguishers.

♦It is not practicable to recharge C02 on board. If these are found to have lost more than 10% of their content weight they should be replaced and returned to an appropriate recharging facility.