Fire Extinguisher Theory & Mntns

Fire Extinguisher Servicing and Maintenance Course

USE AND MAINTENANCEOF

PORTABLE FIRE EXTINGUISHERS

CPT AZMI BIN ADAM

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OC FSITWCIVIL DEFENCE ACADEMY

Outline of Lesson

1. Introduction

2. Extinguishing Agents

3. Fire Extinguisher Theory

3.1 Classes of fire3.2 Classification of Hazards3.3 Ratings of extinguishers3.4 Distribution of extinguishers3.5 Selection of extinguishers3.6 General Requirements of extinguishers3.7 Markings on extinguishers3.8 Theory of Operation

4. Maintenance, Inspection & Recharging 4.1 Maintenance4.2 Inspection4.3 Recharging

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Introduction

In Singapore, the usage of fire extinguishers is principally regulated by the following documents:

a. Fire Precautions in Building (Fire Code)b. SS CP: 55 – Use and Maintenance of Portable Fire

Extinguishersc. SS 232 – Specification for Portable Fire Extinguishers

When are fire extinguishers are required to be fitted ?

The following are extracts taken from the Fire Code

“ All purpose groups, except for Purpose Group I & II (residential floors) shall be provided with portable fire extinguishers.

Portable fire extinguishers shall be constructed in conformity with SS 232

All portable fire extinguishers shall be charged, tested and maintained in fully operational conditions and properly tagged in conformity with SS CP 55”

Therefore, from the extracts, it is obvious that portable fire extinguishers are required for all types of building except only for residential buildings.

2. Fire Extinguishing Agents

In this section, the common extinguishing agents are discussed:

- Water- Carbon Dioxide- Halon- Powder

Portable extinguishers are divided into various categories according to the extinguishing agents they contain.

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2.1 Water

The great majority of fires are extinguished by the use of water by one or a combination of the followings:

- a hose delivery (a solid stream or a spray)- a sprinkler system or a water spray system- a hosereel, and wet/dry system- a water bucket system

Traditionally, the principal method of extinguishing fires has been to direct a solid stream of water into the base of a fire. Another method is to apply water in a spray form over a fire.

The principles of extinguishment of fire by water are:

- cooling and smothering

Advantages of water as a extinguishing agent

At ordinary temperatures, water is heavy and relatively stable liquid

Water has high specific heat capacity (4.2 kJ/Kg of heat at atmospheric pressure)

Water also has good latent heat of vaporization (225kJ/Kg of heat at atmospheric pressure).

When water is converted into steam, its volume increases by about 1600 times. This large volume of steam displaces an equal volume of air surrounding a fire, thus reducing the volume of air available to sustain combustion.

Water is relatively cheap

Water is easily available

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Disadvantages of water

Water in its natural state contains impurities that make water conductive. If water is applied to fire involving LIVE electrical equipment. A continuous circuit might be formed which would conduct electricity and cause a shock to the operator.

Generally, water should not be used on fires involving combustibles (burning) metals as an explosion may occur.

Water should not be used continuously on radioactive substances.

If more water is applied more than necessary, damages may be caused to goods and properties

2.2 Carbon dioxide

Carbon dioxide has been used for many years in the extinguishment of flammable liquids, gas fires and fires involving electrically energized equipment and to a lesser extent, on ordinary combustibles, such as paper, cloth, etc.

Carbon dioxide is effective primarily because it reduces the oxygen content of the atmosphere by dilution to a point where the atmospheres no longer support combustion.

As carbon dioxide is discharge it boils (vaporizes) off rapidly as a gas, extracting heat from the surrounding atmosphere. It is also used for smothering a fire.

However, a minimum concentration of carbon dioxide is needed for extinguishment.

Advantages of carbon dioxide

Non combustible Non conductive of electricity Does not react with most substances. Non toxic No residue It is a gas and can penetrate and spread to all parts of the fire area Easily liquefied and bottled under pressure.

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Disadvantages

Use of carbon dioxide on general fires is limited mostly by:- low cooling capacity; and - enclosure incapable of retaining extinguishing atmosphere.

For deep-seated fires, a high concentration and much longer holding time are required for complete extinguishment.

Gas is not visible. Leaking of gas might cause suffocating atmosphere. A danger to human beings.

Carbon dioxide should normally not be used in occupied spaces unless arrangements can be made to assure evacuation before discharge. The same restriction also applies to spaces where personnel might be present sometimes for maintenance or other purposes.

2.3 Halon

Halons are hydrocarbon in which one or more hydrogen atoms have been replaced by atoms from the halogen series:

Fluorine, Chlorine, Bromine, Iodine

This substitution confers non-flammability as well as flame extinguishment properties to many of the resulting compounds (BCF, BTM). Halons are used widely in portable extinguishers and in fixed total flooding systems.

F Steam

F C Br H+ HBr OH+

F Br(process repeated)

Advantages of Halons

Non conductive of electricity. Non-injurious to delicate electronic equipment. Not messy.

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Disadvantages

Expensive Halons contribute to reductions in OZONE layer in earth’s upper

atmosphere (more severe than CFCs used in HVAC equipment). It also acts as GREENHOUSE gas trapping heat in atmosphere causing GREENHOUSE EFFECT (Global Warming). Montreal Protocal limits the use of Halons by a certain year.

Toxicity (Limit by its concentration and exposure time).

Dry Powder

Powders used to extinguish or control fires are composed essentially of very small particles of an appropriate chemical or chemicals. Different chemicals are effective on different classes of fire.

Powders are classified according to their potential applications, i.e. AB, ABC.[ABC: mono ammonium/ AB: Bicarbonates of sodium & potassium]Used commonly in portable fire extinguishers.

Powder forms a barrier to reduce the oxygen content for sustainable combustion. A crust is formed over the burning material by the action of heat on the powder. This crust enables the material to cool and thus retard the burning.

Advantages

Effective for fires involving plastics, burning metal. Give quick knock-down. When applied, cloud screens flames, enables close attack to be

made on fire. Forms a radiant heat barrier.

Disadvantages

Very messy, not suitable for electronic equipment. Inhaling of chemical may be detrimental to one’s health.

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3 Fire Extinguisher Theory

In this section, the classes of fire, the requirements, the selection of fire extinguishers and the principles of operation are covered in detail.

3.1 Classes of Fire

In Singapore, fires are classified into the following categories:

Class A Fires

These are fires involving the burning of solid combustibles or materials. Examples are wood, furniture, paper, textile, etc.

Class B Fires

Class B fires are fires involving flammable liquids, solvents, oils, paints thinner and flammable gases.

Class C Fires

These are fires involving the burning of live electrical equipment. Examples are electrical mains, transformers, electrical appliances etc.

Class D Fires

These are fires involving the burning of combustible metals. Examples are potassium, magnesium, titanium etc.

3.2 Classification of Hazards

Low Hazard

Where the amount of combustibles or flammable liquids present is such that fires of small size may be expected and these may include:

Offices, classrooms, places of worship, assembly halls and domestic kitchens.

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Medium Hazard

Where the amount of combustibles present is such that fires of moderate size may be expected and these may include:Storage and display areas, motor showrooms, covered car parks, light-industry premises, warehouses not classified as high hazard, shopping areas, laboratories, small painting areas and commercial kitchens.

High Hazard

Where the amount of combustibles present is such that fires of severe magnitude may be expected and these may include:

Exhibition areas, furniture showrooms, wood working premises, vehicle repair workshops, aircraft hangars, warehouses with high-bay (4 m or higher) storage and processes such as flammable liquid handling, paint and dipping.

3.3 Ratings of Extinguishers

Extinguishers are rated in accordance to the extinguishing performance on Class A fire test or Class B fire test as spelt out in SS 232. There is at present no Class C fire test.

Every extinguisher is designated by a number followed by an alphabet, for example, 13A, 27B, etc in accordance to SS 232. The alphabet represents the class of fire that the extinguisher is suited for. The number is the size of fire that the extinguisher is capable of extinguishing.

Class A Fire Test

Figure 1 gives the arrangement in preparation for a Class A fire test.

Woods sticks used for the fire test:

Pinus silvestris, light red meranti or equivalent

Fuel used for the test:

Aviation petrol grade AVGAS 100L or other approved type

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The wooden sticks are stacked in 14 layers on the metal frame as shown in the Figure.

The sticks in each layer are spaced at nominal 100mm centres with nominal 61mm gaps between the sticks.

The sticks laid transversely (layers 2,4,6,8,10,12,14) have length of 500mm + or – 10mm.

The sticks laid longitudinally (layers 1,3,5,7,9,11,13) have lengths equal to the test fire length shown in the Figure, again with a permissible deviation of + or – 10mm.

Test Fire Location

The test fire is sheltered from draughts. The test area does not impede the natural development of the test

fire or effective fire fighting. The wind speed is not greater than 1m/s

Procedure

a. Pour water into the lighting tray to form a layer of at least 30mm deep over the whole base of the tray. Add sufficient fuel to give a burning time of about 2.5 mins.

b. 120secs after fuel ignition withdraw the tray from the wood crib.c. Permit the wood crib to burn for a further 6 min, making it a total

of 8 minutes.d. Operate the fire extinguisher and apply it to the test fire.

ExtinguishersMay be discharged continuously or in successive bursts.

Requirement for Extinguishment

Test fires are considered as extinguished if, for Class A test, all flames are extinguished and there is no recurrence of flaming during the 3 minutes observation period.

If the wood crib collapses during the test, it is to be considered void and a fresh test carried out

Test Criteria

The basic criterion of determining the rating comprises a set of 3 test fires. A rating is achieved by extinguishing in at least 2 out of 3 attempts. A set comprises either:

Class B Fire Test

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A similar regime is carried out for Class B fire test. However, for Class B fire test, petrol is burnt instead of wooden sticks. Refer to SS232 for further details.

3.4 Distribution of Fire Extinguishers

Class A Hazards

For Class A hazard, no person needs to travel more than 15m to reach an extinguisher. Minimum sizes of fire extinguisher for Class A fire hazards are to be selected based on Table 2 subject to the following:

For high hazard occupancy, the minimum rating is 21A. There is to be at least on extinguisher of the minimum size on each

storey/level of building.

Table 2

Maximum Floor Area to be Covered (m)Minimum Extinguisher Rating

Low Hazard Occupancy

Ordinary Hazard Occupancy

High Hazard Occupancy

3A5A8A13A21A27A34A43A55A

1202003205208401080136017202200

601001602604205406808601100

----315405510645825

Notes: For each unit of ‘A’, the minimum floor area to be covered is 40 sq

m for the low hazard, 20 sq m for the medium and 15 sq m for the high.

Consideration is to be given to the special circumstances and the arrangement of the building or floor space to be protected.

It is undesirable to choose a small number of high rating extinguishers or a large number of low rating extinguishers.

Example to meet 100A rating, choose2 x 55A X

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21 x 5A X8 x 13A OK5 x 21A OK2 x 27A plus 7 x 8A OK1 x 43A plus 5 x 13A OK

The travel distance from any point of the floor to the nearest extinguisher must not exceed 15m. This means that more extinguishers in addition to this minimum recommendation may have to be provided.

Problem:

Your advice is sought by a building management to provide portable extinguishers for an office space of approximately 1200 sq m. Please give your opinion on, the number, size and type of extinguishers most suitable for the protection of this space.

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Class B Hazards

For Class B extinguishers, they are to be located such that the travel distances are not to exceed those specified in Table 3.

Table 3Type of Hazard Basic minimum rating Maximum Travel

distance to extinguishers (m)

Low

Medium

High

8B13B34B

70B

144B

3510

15

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Notes Combination of extinguishers of lower ratings may be used to fulfill

the protection requirements of Table 2 for high hazard only. Such combination shall be limited to a maximum of three extinguishers of individual rating of 21 A or higher

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3.5 Selection of Fire Extinguishers

Extinguishers are selected for the specific class or classes of hazards to be protected in accordance to the following recommendations:

Class A hazards : Water types (Only Class A hazards)ABC PowderFoam types

Class B hazards : BC powder

Carbon dioxide

Class C hazards : Carbon dioxideBC powder

Class D hazards : Extinguishers and agents are to be of types approved for use on specific combustible metal hazard

Selection Algorithm

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START

F/EXT

Requirements

AreaCoverage

HAZARD

Availablecost

Agents Classes of Fire

Low

MediumHigh

CLASS A

CLASS B

* 15m Rule* Number Required (Table 2)

* Other Distances* Number required* Preferred Location

. General (See Notes)

. Specific – Environment- Health/Safety- User Capacity


3.6 General Requirements

1 Classification of Extinguishers

Numeral & Letter (Class A & B only)

2 Location

Conspicuously located preferably near to:

Room exitsCorridorsStairwaysLobbiesLandings

In large rooms where visual obstruction is present, provide signs.

3 Special Risks

Sited near to the riskIf special risk is confined in room, position outside the room

4 Atmosphere

5 Cabinets

Cabinets are not to be lockedLocked cabinets: Glass-fronted box to house key

6 Physical Damage

Mechanically protected

7 Height of Extinguisher

Carrying handle is not more than 1.5 m above floor

8 Operating instructions

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. Operating/Maintenance Costs

. Large Number/Small Rating

. Small Number/Large Rating

. Initial Cost


In accordance to SS 232 and presented on the front of extinguisher.

3.7 Marking on Extinguishers

1 General

a) The words : “fire extinguisher”b) Extinguishing medium : water / powder/ carbon

dioxidec) Type : stored or cartridged) Nominal charge : kilograms or litrese) Class of Fire : “Fire Test Rating…..A or B or A, B”f) Method of operation : In prominent letters or diagramsg) Words : appropriate and suitable uses

(symbols and pictures recommended)

2 Warning markings

Examples are:

‘WARNING Do Not Use On Live Electrical Equipment’

‘WARNING: Do Not Use On Flammable Liquid Fires’

3 Other Information

Extinguishers are to be clearly marked with the following:

a) Manufacturer’s nameb) Number & date of applicable Singapore Standardc) Temperature range for satisfactory operationd) Year for manufacturee) Test pressure & working pressuref) Manufacturer’s identification of medium

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3.8 Theory of Operation

Two methods of operation are commonly used here. The first method is the gas cartridge type and the second method is the stored pressure type. The water portable extinguisher is used to show the two types of operation.

Gas cartridge

The water content of this plastic-lined cylinder is generally 9 or 6 litres and the expellent gas, usually CO2, is contained in a cartridge fitted inside the body of the extinguisher. (See Figure 2)

The expellent liquid is pure water, although non-corrosive antifreeze compounds can be added. The operating pressure is in the region of 10 bar(1000kPa).

Firstly, the safety pin is removed. The application of pressure on the operating lever causes a pressure disc on the cartridge to be pierced, and at the same time opens a control valve. The release of gas exerts pressure on the surface of the water, forcing it up the discharge tube and out through the hose and nozzle. The operating lever can control the discharge.

Stored pressure

This is of similar construction to the gas-cartridge type and of similar capacities, the difference being that the whole container is pressurised. (See Figure 3). Air or nitrogen is pumped into it through a special adaptor in the operating head until the pressure reaches about 10 bar.

Removing the safety pin or plug and squeezing the operating lever operates the extinguisher. This opens the control valve and allows the pressurized air to expel the water in the container. Again, the operating lever can control the discharge.

4. Maintenance, Inspection, and Recharging

4.1 Maintenance

Frequency of Maintenance

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Extinguishers shall be subjected to maintenance not more than one year apart or when specifically indicated by an inspection. Maintenance procedure shall be performed in accordance with 4.3.2.

Extinguishers taken away for maintenance or recharge shall have in replacement, extinguishers of the same type and at least equal rating.

Maintenance Procedures

Maintenance procedures shall include a thorough examination of the three basic elements of an extinguisher:

a) Mechanical parts;

b) Extinguishing agent; and

c) Means of expulsion.

Exception: It is not necessary during the annual maintenance to internally examine stored pressure extinguishers equipped with pressure indicators or gauges or carbon dioxide extinguishers. However, such extinguishers shall be thoroughly examined externally in accordance with the applicable items of 4.3.2 (a).

Record Keeping

Each extinguisher shall have a tag or label securely attached that indicates the month and year the maintenance was performed and shall identify the person and organization performing the service. The same record tag or label shall indicate if recharging was also performed.

In addition to the required tag or label (see 4.3.3), a permanent file record should be kept for each extinguisher. This file record should include the following information as applicable:

a) The maintenance date and the name of person or agency performing the maintenance;

b) The date when last recharged and the name of person or agency performing the recharge;

c) The hydrostatic retest date and the name of person or agency performing the hydrostatic test;

d) The date of the next recharge.

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Inspection Procedures

Periodic inspection of extinguishers shall include a check of at least the following items:

a) Located in its designated place;

b) No obstruction to access or visibility;

c) Operating instructions on the extinguisher label legible and facing outward;

d) Seals and tamper indicators not broken or missing;

e) Determine fullness by weighing or “hefting”;

f) Examine for obvious physical damage, corrosion, leakage or clogged nozzle;

g) Pressure gauge reading or indicator in the operative range or position.

4.2 Inspection

Frequency of Inspection

It is recommended that extinguisher should be inspected monthly or at more frequent intervals when the following circumstances exist:

a) High frequency of fires in the past;

b) Severe hazards;

c) Susceptibility to tampering, vandalism, or malicious mischief;

d) Possibility of, or experience with, theft of extinguishers;

e) Locations that make extinguishers susceptible to mechanical injury;

f) Possibility of visible or physical obstructions;

g) Exposure to abnormal temperatures or corrosive atmospheres;

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h) Characteristics of extinguishers, such as susceptibility to leakage.

4.3 Recharging

General

All extinguishers shall be recharged after use or as indicated by an inspection or when performing maintenance. When performing the recharging, the recommendations of the manufacturers shall be followed. For recharge chemicals, see 4.4.3.1. (Refer to Appendix C for general safety guidelines for recharging.)

Frequency of Recharging

All extinguishers shall be completely emptied and recharged at intervals as follows:

a) Every 2 1/2 years - water (stored pressure) chemical foam

mechanical foam (gas cartridge)mechanical foam (stored pressure)

b) Every 5 years - water (gas cartridge)powder (gas cartridge)powder (stored pressure)

c) Every 10 years - carbon dioxidehalon 1301halon 1211

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Hydrostatic Test

Extinguishers shall be hydrostatically tested at intervals not exceeding those specified

Hydrostatic test interval for extinguishers

Extinguisher type Test interval (Years)

Cartridge operated water

Stored pressure water

Foam

AFFF ( Aqueous Film Forming Foam)

Powder type with stainless steel body

Carbon dioxide

Powder type, stored pressure, with mild steel shells or aluminium body

Powder type, cartridge or cylinder operated, with mild steel body

Bromochlorodifluoromethane (Halon 1211)

Bromotrifluoromethane (Halon 1301)

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5

5

5

5

10

5

5

10

10

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Figure 1

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Figure 2

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Figure 3

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Fire Extinguisher Theory & Mntns

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