Automatic Fire Extinguishing System

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AUTOMATIC SPRINKLER SYSTEMS

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1. INTRODUCTION Automatic sprinklers are devices for automatically distributing water upon a fire in sufficient quantity either to extinguish it entirely or to control its spread. The water is fed to the sprinklers through a system of piping, ordinarily suspended from the ceiling, with the sprinklers placed at intervals along the pipes. The orifice of the fusible link automatic sprinkler is normally closed by a disk or cap held in place by a temperature sensitive releasing element. The terms sprinkler protection, sprinkler installations and sprinkler systems usually signify a combination of water discharge devices (sprinklers), one or more sources of water under pressure, water flow controlling devices (valves), distribution piping to supply the water to the discharge devices and auxiliary equipment, such as alarms and supervisory devices. 2. DEVELOPMENT OF AUTOMATIC SPRINKLERS The forerunners of the automatic sprinkler were the perforated pipe and the open sprinklers. These were installed in a number of mill properties from 1850 to 1880. The systems were not automatic, the discharge openings in the pipes often clogged with rust and foreign materials and water distribution was poor. Open sprinklers, an improvement over perforated pipes, consisted of metal bulbs with numerous perforations attached to piping and intended to give improved water distribution. This system was only slightly better than the perforated pipe. The idea of automatic sprinkler protection, whereby heat from a fire opens one or more sprinklers and allows the water to flow, dates back to about 1860. Its practical application however, began about 1878. This sprinkler, while very crude when compared with modern devices, gave generally good results and proved conclusively that automatic sprinkler protection was both practical and valuable. 3. VALUE OF AUTOMATIC SPRINKLER PROTECTION Automatic sprinklers are particularly effective for life safety because they give warning of the existence of fire and at the same time apply water to the burning area. With sprinklers there are seldom problems of access to the seat of the fire or of interference with visibility for fire fighting due to smoke. While the downward force of the water discharged from sprinklers may lower the smoke level in a room where a fire is burning, the sprinklers also serve to cool the smoke and make it possible for persons to remain in the area much longer than they could if the room were without sprinklers. Automatic sprinklers, properly installed and maintained, provide a highly effective safeguard against the loss of life and property from fire. The NFPA has no record of __________________________________________________________________________________ 2

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multiple death fire (a fire which kills three or more people) in a completely sprinkled building where the system was properly operating, except where an explosion occurred or flash fire killed victims prior to the system’s operation. In addition to the saving in direct fire losses due to sprinkler protection, there is saving represented by the freedom from business interruption. There also is an undetermined but possibly even greater reduction in conflagration and exposure losses, which reasonably may be attributed to automatic sprinkler protection. The destruction of property and its adverse association and sometimes permanent effect upon business often is a great hardship not only to the owner, tenants and employees but also to the community as a whole. A properly installed sprinkler system operating in a timely manner will generate less water damage than the later application of hose streams by fire officers. Accidental discharge of water from an associate sprinkler system due to defects in sprinklers, water control devices, piping or associated equipment, is very rare. 4. DESIGN CONSIDERATIONS In planning for a system many factors must be considered. They can, however, be broadly grouped into three categories: a. b. c.

the sprinkler system itself; hazards of occupancy; and location of sprinklers.

5. THE SPRINKLER SYSTEMS a

Types of sprinkler systems There are five major classifications of automatic sprinkler systems. Each type of system includes piping for carrying water from a source of supply to the sprinklers in the area under protection. The five major classifications of systems are (See Appendix I for schematic illustrations of systems): Wet pipe systems – These systems employ automatic sprinklers attached to a piping system containing water under pressure at all times. When a fire occurs, individual sprinklers are actuated by the heat, and water flows through the sprinklers immediately. This type of system is generally used whenever there is no danger of the water in the pipes freezing; and wherever there are no special conditions requiring one of the other types of systems. (1)

Dry pipe systems – These systems have automatic sprinklers attached to piping which contains air or nitrogen under pressure. When a sprinkler is opened by heat from a fire, the pressure is reduced to the point where water pressure on the supply side of the dry pipe valve can force open the valve. The (2)

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water flows into the system and out through any opened sprinklers. They are used only in freezing environment. According to fire records, more sprinklers open on the average at fires with dry pipes than with wet pipe systems: this tends to show that the control of fire is not as prompt with dry pipe systems. Preaction systems – These systems are systems in which there is air in the piping that may or may not be under pressure. When a fire occurs, a supplementary fire detecting device in the protected area is actuated. This opens a water control valve which permits water to flow into the piping system before a sprinkler is activated. When sprinklers are subsequently opened by the heat of the fire, water flows through the sprinklers immediately – the same as in wet pipe system. Preaction systems are designed primarily to protect properties where there is danger of serious water damage as a result of damaged automatic sprinklers or broken piping. (3)

The principal difference between a preaction system and a dry pipe system is that in the preaction system, the water supply valve is actuated independently of the opening of sprinklers; that is, the water supply valve is opened by the operation of an automatic fire detection system and not by the fusing of a sprinkler. The preaction system has several advantages over a dry pipe system. The valve is opened sooner because the fire detectors has less thermal lag than sprinklers. The detection system also automatically rings an alarm. Fire and water damage is decreased because water is on the fire more quickly and the alarm is given when the valve is opened. Because the sprinkler piping is normally dry, preaction systems are nonfreezing, and therefore, applicable to dry pipe service. Deluge Systems – These systems have all sprinklers open at all times. When heat from a fire actuates the fire detecting device, the deluge valve opens and water flows to, and is discharged from all sprinklers on the piping system, thus deluging the protected areas. (4)

The purpose of a deluge system is wet down an entire fire area by admitting water to sprinklers that are open at all times. By using sensitive detectors operating on the rate-of-rise or fixed temperature principle, or controls designed for individual hazards, it is possible to apply water to a fire more quickly and with wider distribution than with systems whose operation depends on opening of sprinklers only as the fire spreads. Deluge systems are suitable for various extra hazard occupancies in which flammable liquids or other hazardous materials are handled or stored and where there is a possibility that fire may flash ahead of the operation of ordinary automatic sprinklers. b Automatic Sprinklers __________________________________________________________________________________ 4

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(1)

General

Automatic sprinklers are thermosensitive devices designed to react at predetermined temperatures by automatically releasing a stream of water and distributing it in specified patterns and quantities over designated areas. Since they were introduced in the latter part of the 19th century, the performance and the reliability of automatic sprinklers has been continually improved through experience and the efforts of manufacturers and testing organizations. (2)

Operating Principles of Automatic Sprinklers

Under normal conditions, the discharge of water from an automatic sprinkler is restrained by a cap or valve held tightly against the orifice by a system of levers and links or other releasing devices pressing down on the cap and anchored firmly by struts on the sprinkler. Attached to the frame of the sprinkler is a deflector or distributor against which the stream of water is directed and converted into a spray designed to cool or protect a certain area. The amount of water discharged depends upon the flowing water pressure and the size of the sprinkler orifice. (3)

Operating Elements

The most common types of operating elements are the fusible and the frangible types. Other styles of the thermosensitive operating elements may be, or have been employed to provide automatic discharge, such as bimetallic discs, fusible alloy pellet or chemical pellets. ( See Annex C for diagrammatic illustrations of the operating elements of the fusible and frangible sprinklers). (a)

Fusible sprinklers – A common fusible style automatic sprinkler operates upon the fusing of a metal alloy of predetermined melting point. Various combinations of levers, struts and links or other soldered members are used to reduce the force acting upon the solder so that the sprinkler will be held closed with the smallest practical amount of metal and solder. This minimizes the time of operation by reducing the mass of fusible metal to be heated.

(b)

Frangible sprinklers – A second style of operating element utilizes a frangible bulb. The small bulb, usually of pyrex glass, contains a liquid which does not completely fill the bulb, leaving a small air bubble entrapped in it. As the liquid is expanded by heat,

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the bubble is compressed and finally absorbed by the liquid. As soon as the bubble disappears, the pressure rises infinitely and the bulb shatters, releasing the valve cap. The exact temperature is regulated by adjusting the amount of liquid and the size of the bubble when the bulb is sealed. (4)

Temperature Rating of Automatic Sprinklers

Automatic sprinklers have various temperature ratings that are based on standardized tests in which a sprinkler is immersed in a liquid and the temperature of the liquid is raised very slowly until the sprinkler operates. The recommended maximum room temperature is generally closer to the operating temperature for frangible bulb than for soldered fusible-element sprinklers because solder begins to lose its strength somewhat below its actual melting point. The temperature rating of all solder style automatic sprinklers is stamped upon the soldered link. For other types of thermosensitive elements, the temperature rating is stamped upon some of the releasing parts. (See Annex D for examples of colour coding for temperature ratings of sprinklers). (5)

Types of Sprinklers

(a)

Standard Sprinklers – Due to the design of the deflector, the solid stream of water issuing from the orifice of a standard sprinkler is broken up to form an umbrella shaped spray. The pattern is roughly that of a half sphere filled with spray. Relatively uniform distribution of the water at all levels below the sprinklers is characteristic of a standard sprinkler. Standard sprinklers are made for installation in an upright or pendent position.

(b)

Recessed sprinklers – A recessed sprinkler has part or most of the body of the sprinkler, other than the part which connects to the piping, mounted within a recessed housing. Operation is similar to that of standard pendent sprinkler.

(c)

Flushed sprinklers – Sprinklers of special designs but with the same water discharge pattern as standard pendent sprinklers are available for use wet system piping concealed above the ceilings in areas where appearance is important. The special design allows a minimum projection of the working parts of the sprinkler below the ceiling in which it is installed without adversely affecting the heat sensitivity or the pattern of water distribution. Only the ceiling plate and thermosensitive assembly are visible from the floor when

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these sprinklers are installed. When a fire occurs and the thermosensitive element operates, the deflector drops to a position below the ceiling and the water discharge commences. (d)

Concealed Sprinklers – A concealed sprinkler has its entire body, including the operating mechanism, above its concealing cover plate. When a fire occurs, the cover plate drops, exposing the thermosensitive assembly.

(e)

Ornamental Sprinklers – Ornamental sprinklers are automatic sprinklers that have been decorated by attachments or by plating or enamelling to give desired surface finishes.

(f)

Dry Sprinklers – Dry sprinklers are used to provide sprinkler protection freezing areas where individual sprinklers are supplied from a drop or riser pipe from a wet pipe system outside the freezing area. A seal is provided at the entrance of the dry sprinkler to prevent water from entering until the sprinkler fuses.

(g)

Large Drop Sprinklers – The deflector of a large drop sprinkler is specially designed, and that combined with the velocity as to enable the spray to penetrate strong up drafts generated by high challenge fires.

(h)

Sidewall Sprinklers – Sidewall sprinklers have the components of standard sprinklers except for a special deflector which discharges most of the water toward one side in a pattern somewhat resembling one quarter of a sphere. A small proportion of the discharge wets the wall behind the sprinkler. The forward horizontal range is greater than that of a standard sprinkler. Sidewall sprinklers are used in areas where the usual sprinkler pipes could be objectionable in appearance. The directional character of the discharge from sidewall sprinklers make them applicable to occasional special protection problems. They may be installed to give discharge in any desired direction.

(i)

Extended Coverage Sidewall Sprinklers – These are special sidewall sprinklers used in the horizontal position that have larger areas of coverage than allowed for conventional sidewall sprinklers.

(j)

Open Sprinklers – Open sprinklers are standard automatic sprinklers, or sidewall automatic sprinklers with the valve cap and heat responsive elements omitted. Open sprinklers are used in deluge systems. The water distribution pattern and the density of

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the discharge of the open system are designed to be appropriate for the hazard to be protected. (k)

Intermediate Level Sprinklers – Intermediate sprinklers, sometimes referred to as rack storage sprinklers, have large discs designed to shield the thermosensitive assembly from impingement from the spray of sprinklers, suspended at higher levels. Without the protective discs, the impinging water would cool the thermosensitive element and retard sprinkler operation.

(l)

Quick Response Sprinklers – Except for the sensitivity of the fusible element, quick response sprinklers possess the same characteristics as a standard sprinkler of the same type. Quick response sprinklers will respond more quickly to a fire than standard sprinklers.

6. Hazards of Occupancy Automatic sprinkler systems of one type or another have been designed to extinguish or control practically every known type of fire in practically all materials in use today. It is essential, however, that for a given hazard the proper system be used. For the purposes of evaluating hazards, three main classes of occupancy are usually recognized in most design codes. Schedules of pipe sizes, spacing of sprinklers, sprinkler discharge densities and water supply requirements differ from each in order to provide protection appropriate for the hazard. The three main classifications are: a. Light Hazard Class – includes occupancies where the quantity and combustibility, or both, of materials is low and fires with relatively low rates of heat release are expected. b. Ordinary Hazard Class – in general, includes ordinary mercantile, manufacturing and industrial properties. c. Extra Hazard Class – involve a wide range of variables which may produce severe fires. Some conditions require more than ordinary sprinkler protection in order to provide dependable fire extinguishment and control. Sprinkler experience shows that occupancies which involve high piled combustible stocks flammable and combustible liquids, combustible dusts and fibres, large quantities of light or loose combustible materials and chemicals and explosives can permit rapid spread of fire and often cause the opening of excessive numbers of sprinklers with disastrous results. Complete automatic sprinkler protection with strong water supplies will usually control fires in occupancies containing these hazardous conditions, provided the

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severity of the hazards is plainly recognized and the sprinkler system is appropriately designed for the hazards. 7. Location of Sprinklers The fundamental idea in locating and spacing sprinklers in a building is to make sure there is no unprotected place, however unexpected, where a fire can start. In other words, no matter where a fire starts, there must be one or more sprinklers located in relation to that particular point that will operate promptly and discharge water when heat from the fire reaches them. Furthermore, there should be no direction that fire can spread in which it will not encounter other sprinklers to stop its progress. Most codes treat specifically a number of locations where the need for sprinklers is sometimes questioned. These include locations such as stairways and vertical shafts; deep, blind and concealed spaces; ducts; basements or subfloor spaces, attics and lofts; and under decks, tables, exhaust hoods, canopies and outdoor platforms. The location of sprinklers on a line of pipe, and the location of the lines in relation to each other determine the size of area protected by each sprinkler. Most codes give a definite maximum area of cover for each sprinkler, depending principally upon the severity of the occupancy hazard and, to a lesser degree, on the type of ceiling or roof construction above the sprinklers. In addition to limits on the maximum distance between sprinklers or lines and between lines, certain limits of clearance have been established between sprinklers and structural members, such as beams, girders and trusses, to avoid obstructing water being discharged from sprinklers. If a sprinkler is placed too closely to a beam that deflects the normal discharge patterns of the water, the area of protection for that sprinkler is considerably reduced and fire has a chance for additional growth. This caused more sprinklers to operate than should have been necessary. The distance between sprinklers and the ceiling is important. The closer sprinklers are placed to the ceiling the faster they will operate. However, except for continuos smooth ceilings, locating them too close to the ceiling is more likely to result in serious interference to lateral distribution of water from sprinklers by structural members.

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WATER SPRAY SYSTEMS

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1

INTRODUCTION A water spray system is a special fixed pipe system connected to a reliable supply of fire protection water, and equipped with water spray nozzles for specific water discharge and distribution over the surface or area to be protected. The piping system is connected to the water supply through an automatically or manually actuated valve which initiates the flow of water. The term water spray refers to the use of water that has a predetermined pattern, particle size, velocity and density and that is discharged from specially designed nozzles or devices. Water spray for fire protection has been called water fog, fog or by trade name designations applied by equipment manufacturers. (See Annex F of water spray nozzles). There is no sharp line of demarcation between water spray protection and sprinkler protection. The discharge from nozzles or sprinklers producing a spray pattern differs only in the particular form of the spray and the other variables indicated in the above paragraph. In some cases, the same device may serve both purposes. Fixed water spray systems are specifically designed to provide optimum control, extinguishment, or exposure protection for special fire protection problems. They are not intended to replace automatic sprinkler systems, but they may be independent of, or supplementary to, other forms of protection. 2. APPLICATION OF WATER SPRAY PROTECTION Fixed water spray systems are most commonly used to protect flammable liquid and gas tank age, piping and equipment such as transformers, oil switches, and rotating electrical machinery, and openings in fire walls and floors through which conveyors pass. The type of water spray required for any particular hazard will depend on the nature of the hazard and the purpose for which the protection is provided. Generally, water spray can be used effectively for any or a combination of the following purposes: a. Extinguishment ---- Extinguishment of fire by water spray i.e. accomplished by cooling, smothering from steam produced, emulsification of some liquids, dilution in some cases, or a combination of these factors. b. Controlled Burning ---- with its consequent limitation of fire spread, controlled burning may be applied if the burning combustible materials are not susceptible to extinguishment by water spray, or if extinguishment is not desirable.

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c. Exposure Protection ---- Exposure protection is accomplished by application of water spray directly to the exposed structures or equipment to remove or reduce the heat transferred to them from the exposing fire. Water spray curtains mounted at a distance from the exposed surface are less effective than direct application. d. Prevention of Fire ---- It is sometimes possible to use water spray to dissolve, dilute, disperse or cool flammable or combustible materials before they can ignite from an exposing ignition source. Water spray protection is advantageous in meeting the above mentioned purposes when it is applied to the following types of materials or equipment: a. Ordinary combustible materials such as paper, wood and textiles, particularly to extinguish certain types of fires involving combustible liquids. b. Electrical equipment installations, such as transformers, oil switches, and rotating electrical machinery. c. Flammable gas and liquids, particularly to control fires in these materials and to extinguish certain types of fires involving combustible liquids. d. Flammable liquid and gas tanks, processing equipment and structures, as protection for those installations against exposure fire. e. Open cable trays and runs containing electrical cables or tubing. 3. DESIGN CONSIDERATIONS The practical location of the piping and nozzles with respect to the surface with which the spray is to be applied, or to the zone in which the spray is to be effective, is determined largely by the physical arrangement and protection needs of the installation requiring protection. Once the criteria are established, the size (rate of discharge) of nozzles to be used, the angle of the nozzle of discharge cone and the water pressure needed can be determined. The first factor to determine is the water density required to extinguish the fire or to absorb the expected heat from exposure or heat of combustion. When this is determined, a nozzle may be selected that will provide that density at a velocity adequate to overcome air currents and to carry the spray to the equipment to be protected. Each nozzle selected must also have the proper angle of discharge to cover the area to be protected by the nozzle. The determination of the proper density to be used for extinguishment requires considerable engineering judgement and, in the case of flammable or combustible

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liquids, depends on such characteristics of the fuel as vapour pressure, flash point, viscosity, solubility, and specific gravity. Once the type of nozzle has been selected and the location and spacing to give the desired area coverage has been determined, hydraulic calculations are made to be establish the appropriate pipe sizes and water supply requirements. When water spray is to be used for the fire protection of oil-filled electrical equipment, such as transformers and large switch gear, special care must be taken to provide safe electrical clearances. Many factors govern the size of a water spray system, including the nature of hazard or combustibles involved, amount and type of equipment to be protected, adequate of other protection, and the size of the area which could be involved in a single The size of the system needed may be minimized by taking advantage of possible subdivision by fire walls, by limiting the potential spread of flammable liquids by dikes, curbs or special drainage, by water curtains or heat curtains, or by combinations of these features.

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FOAM SYSTEMS

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1

INTRODUCTION Fire fighting foam is an aggregate of gas filled bubbles formed from aqueous solutions of specially formulated concentrated liquid forming agents. The gas used is normally air, but in certain applications may be an inert gas. Since foam is lighter than flammable liquids, it floats on all flammable or combustible liquids, producing an air excluding, cooling, continuous layer of vapour sealing, water bearing material that halts or prevents combustion. Foam is produced by mixing a foam concentrate with water at the appropriate concentration and then aerating and agitating the solution to form the bubble structure. Some foams are capable of producing a vapour sealing film of surface active water solution on a liquid surface. Some are meant to be used as large volumes of wet gas cells for inundating surfaces and filling cavities. Foams are defined by their expansion ratio, which is the ratio of final foam volume to original foam solution volume before adding air. They are arbitrarily subdivided into three ranges: a. Low Expansion Foam ---- expansion up to 20:1 b. Medium Expansion Foam ---- expansion 20 to 200:1 c. High Expansion Foam ---- expansion 200 to 1000:1

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DEVELOPMENT OF FOAM SYSTEMS Foam was first used to extinguish flammable liquid fires in the early 1900s when foam was generated by mixing solutions of sodium bicarbonate and aluminium sulphate containing a foam stabilizing agent. This was known as “chemical foam” and was still frequently used in extinguishers until quite recently. Although larger systems were made for tank fire protection the sheer size of the systems and the problems of maintenance made them both costly and unsatisfactory. The general use of foam began to grow rapidly in the 1930s with the development of foaming agents and foam generating equipment which could produce foam in relatively simple equipment by entraining air. The foam so produced was known as “mechanical foam” to distinguish it from “chemical foam”.

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USES & LIMITATIONS OF FIRE FIGHTING FOAMS Low expansion foam is principally used to extinguish burning flammable or combustible liquid spill or tank fires by application to develop a cooling, coherent blanket. Foam is the only permanent extinguishing agent used for fires of this type. A foam blanket covering the tank’s liquid surface can prevent vapour transmission for some time, depending upon the stability and depth of the foam.

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Fuel spills are quickly rendered safe by foam blanketing. Foams may be used to diminish or halt the generation of flammable vapours from non burning liquids or solids and may be used to fill cavities or enclosures where toxic or flammable gases may collect. Foams of the medium or high expansion type may be used to fill enclosures such as basement room areas or holds of ships where fires are difficult or impossible to reach. Here foams act to halt convection and access to air for combustion. Their water content also cools and diminishes oxygen by steam displacement. Foams of this type may be used to control liquified natural gas spill fires and help disperse the resulting vapour cloud. Foam breaks down and vaporizes its water content under attack by heat and flame. It therefore must be applied to a burning liquid surface in sufficient volume and rate to compensate for this loss, with an additional amount applied to guarantee a residual foam layer over the extinguished liquid. Foam is unstable, and may be easily broken down by a physical or mechanical force such as a water hose stream. Certain chemical vapours or fluids may also quickly destroy foam. When certain other extinguishing agents are used in conjunction with foam, severe breakdown of the foam may occur. Turbulent air or violently uprising combustion gases from fires may divert foam from the burning area. Foam solutions are conductive and therefore not recommended for use on electrical fires. If foam is used, a spray is less conductive than a straight stream. However, because foam is cohesive and contains materials that allow water to conduct electricity, foam spray is more conductive than water spray. 4

TYPES OF FOAM There are a number of types of foaming agents available, known as foam concentrates, some of which are designed for specific applications. Some are suitable for extinguishing all types of flammable liquids, including water soluble and foam destructive liquids. Descriptions of the common types of foam follow: a. Aqueous Film-Forming Agents (AFFF) - AFFF agents are composed of synthetically produced materials that form air foams similar to those produced by the protein based materials. In addition, these foaming agents are capable of forming water solution films on the surface of flammable hydrocarbon liquids, hence the term aqueous film-forming foam. b. Fluoroprotein-Foaming Agents (FP) - The concentrates utilised for generating fluoroprotein foams are similar in composition to protein foam concentrates, but in addition to protein polymer they contain fluorinated surface active agents that confer a “fuel shedding” property to the foam generated. This makes them particularly effective for fire fighting conditions where the foam becomes coated with fuel, such as in the method of subsurface

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injection of foam for tank fire fighting and nozzle or monitor foam applications where the foam may be often be plunged into the fuel. Fluoroprotein foams are very effective for in-depth crude petroleum or other hydrocarbon fuel fires because of this fuel shedding property. c. Film-Forming Fluoroprotein Agents (FFFP) – FFFP agents are composed of protein together with film-forming fluorinated surface action agents, which makes them capable of forming water solution films on the surface of flammable liquids, and of conferring a fuel shedding property to the foam generated. d. Protein Foaming Agent (P) – Protein type air foams utilize aqueous liquid concentrates proportioned with water for their generation. These concentrates contain high molecular weight natural proteinaceous polymers derived from a chemical digestion and hydrolysis of natural protein solids. e. Alcohol Type Foaming Agents (AR) – Air foams generated from ordinary agents and subject to rapid breakdown and loss of effectiveness when they are used on fires that involve fuels which are water soluble, water miscible or of a “polar solvent” type. Certain special foaming agents, called alcohol type concentrates, have therefore been developed. These alcohol resistant concentrates are proprietary compositions of several types, some containing a protein, fluoroprotein, or an aqueous film-forming concentrate base. 5. FOAM GENERATION The process of producing and applying fire fighting air foams to hazards requires three separate operations, each of which consumes energy. They are: a. b. c.

the proportioning process the foam generation phase, and the distribution method

In general practice, air foam generation and distribution occur nearly simultaneously within the same device. There are also many types of proportioning. In certain portable devices, all three functions are combined into a single device. a.

Foam Concentrate Proportioners

So that a predetermined volume of liquid foam concentrate may be mixed with a water stream to form a foam solution of fixed concentration, the following two general methods are used: (1)

Methods that utilize the pressure energy of the water stream by venturi action and orifices to induct concentrate.

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(2) 6

Methods that utilize external pumps or pressure heads to inject concentrate into the water stream at a fixed ratio to flow

FOAM INSTALLATIONS The types of foam installations are: a

Fixed Foam Systems – These are complete installations piped from a central foam station, discharging through fixed delivery outlets to the hazard to be protected.

b

Semifixed Foam Systems – The type which the hazard is equipped with fixed discharge outlets connected to piping which terminates at a safe distance. Necessary foam producing materials are transported to the scene after the fire starts and are connected to the piping

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HALON SYSTEMS

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1. INTRODUCTION Halogenated extinguishing agents are hydrocarbons in which one or more hydrogen atoms have been replaced by atoms from the halogen series: Fluorine, chlorine, bromine or iodine. This substitution confers not only non flammability, but flame extinguishment properties to many of the resulting compounds. Because they are either gases or liquids that rapidly vaporize halons leave no corrosive or abrasive residue after use. They are non-conductors of electricity and have high liquid densities which permit use of compact storage containers. The areas of major Halon use are for the protection of electrical and electronic equipment, petroleum production facilities, engine compartments and other areas where rapid extinguishment is important, where damage to equipment or materials or clean up after use must be minimized. The extinguishing mechanism of the halogenated agents is not clearly understood. However, a chemical reaction undoubtedly occurs which interferes with the combustion process. The agents act by removing the active chemical species involved in the flame chain reaction while all the halogens are active in this way, bromine is much more effective than chlorine or fluorine. 2. DEVELOPMENT OF HALOGENATED AGENTS Prior to 1945, three halogenated fire extinguishing agents were widely used: Carbon tetrachloride (Halon 104), methyl bromide (Halon 1001) and chlorobromomethane (Halon 1011). The earliest Halon 104, became available in the early 1900sand found immediate wide use in portable hand pump extinguishers. Its main advantages were electrical non conductivity and lack of residue following application. In the late 1920s, Halon 1001 was found to have greater extinguishing potential than Halon 104. Because of its high vapour toxicity it was never widely used in portable extinguishers. Halon 1011 was developed in Germany in 1939-40 as a replacement for Halon 1001, but its use did not become widespread until after World War II. For toxicological reasons, however, concern about using these 3 early halogenated agents gained significant momentum during the early 1960s. Except for a few Halon 1001 and Halon 1011 systems that may still be in service, systems containing these 3 halogenated agents have been removed from service. In 1947, the Purdue Research Foundation performed a systematic evaluation of more than 60 new extinguishing agents. Simultaneously, the US Army Chemical Centre undertook toxicological investigations of these same compounds. From these tests, 4 halogenated agents bromotrifluoromethane (Halon 1301), bromochlorodifluoromethane (Halon 1211), dibromodifluoromethane (Halon 1202), and dibromotetrafluoromethane (Halon 2402) were selected for further evaluations in specific applications. From these further tests, Halon 1301 was determined to be the

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second most effective and least toxic of the group, while Halon 1202 was the most effective but also the most toxic. The concept of using halogenated agents in commercial total flooding systems seems to have originated between 1962 and 1964. During 1966, attention began to focus on the use of Halon 1301 to protect computer rooms and electronic data processing equipment. 3. CHEMICAL COMPOSITION AND CLASSIFICATION The halogenated extinguishing agents are currently simply known as halons, and the Halon system for naming the halogenated hydrocarbons was devised by the US Army Corps of Engineers. An example is Halon 1301. The first digit of the number represents the number of carbon atoms in the compound molecule; the second digit, the number of fluorine atoms; the third digit, the number of chlorine atoms; the fourth digit, the number of bromine atoms; and the fifth digit, the number of iodine atoms. If the fifth digit is a zero, it is not expressed, bromotrifluoromethane (BrCF3), for example, is referred to as Halon 1301 (not 13010), although its chemical formula shows one carbon atom, three fluorine atoms, no chlorine atom, one bromine atom, and no iodine atom. The three halogen elements commonly found in extinguishing agents are fluorine, chlorine and bromine. Substitution of a hydrogen atom in a hydrocarbon with these three halogens influences the relevant properties in the following manner: Fluorine----imparts stability to the compound, reduces toxicity, reduces boiling points, increases thermal stability. Chlorine----imparts fire extinguishing effectiveness, increases boiling point, increases toxicity, reduces thermal stability. Bromine----same effects as chlorine, but to a greater degree. Thus compounds containing combinations of fluorine, chlorine and bromine can possess varying degrees of extinguishing effectiveness, chemical and thermal stability, volatility and toxicity. 4. TOXIC & IRRITANT EFFECTS The toxicology of Halon 1301, Halon 1211 and Halon 2402 has been studied extensively in both animals and humans. As a result, safety guidelines for these agents can be written. Animals exposed to Halon concentrations below lethal levels exhibit two distinct types of toxic effects:

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a. central nervous system changes, such as tremors, convulsions, lethargy and unconsciousness at high airborne concentrations (above 30% by volume for Halon 1301 and 10% for Halon 1211); and b. cardiovascular effects including hypertension, decreased heart rate, and occasional cardiac arrhythmia (lack of rhythm in the heartbeat). Effects are transitory and disappear rapidly after exposure. The inhalation of many halocarbons and hydrocarbons can make the heart abnormally sensitive to elevated adrenaline levels, resulting in cardiac, arrhythmia and possibly death. This phenomenon has been referred to as cardiac sensitization. Human exposures to both Halon 1301 and Halon 1211 have shown that Halon 1301 concentrations up to 7% by volume, and Halon 1211 concentrations of 2% to 3% by volume have little noticeable effect on the subject. At Haoln 1301 concentrations between 7% and 10% and Halon 1211 concentrations between 3% and 4%, subjects experienced dizziness and tingling of the extremities, indicating mild anaesthesia. At Halon 1301 concentrations above 4% to 5%, the dizziness becomes pronounce, the subjects feel as if they will lose consciousness and physical and mental dexterity is reduced. From the extensive medical data available, the following exposure guidelines have been produced for use of Halon 1301, Halon 1211 and halon 2402: Concentration Percentage by Volume

Permitted time of Exposure

Halon 1301

Up to 7 7-10 10-15 above 15

15 mins 1 min 30 secs Prevent exposure

Halon 1211

Up to 4 4-5 above 5

5 mins 1 min Prevent exposure

Halon 2402

0.05

10 mins 1 min

Consideration of life safety during use of halogenated agents also must include the effects of breakdown products, which have a relatively higher toxicity to humans. Decomposition of halogenated agents takes place on exposure to flame, or to surface temperatures above approximately 482ºC. In the presence of available hydrogen (from water vapour or the combustion process itself), the main __________________________________________________________________________________ 22

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decomposition products of Halon 1301 are hydrogen fluoride, hydrogen bromide and free bromine. The decomposition products of Halon 1211 and Halon 2402 are similar, but in the case of Halon 1211 include hydrogen chloride and free chlorine as well. When used as intended, no significant adverse health effects have been reported from the use of Halon 1301 or Halon 1211 as a fire extinguishant since their introduction into the market place 30 years ago. 5

APPLICATION SYSTEMS The system consists of a supply of agent, a means for releasing or propelling the agent from its container, and one or more discharge nozzles to apply the agent into the hazard or directly onto the burning object. The system may also contain other elements, such as one or more detectors, remote and local alarms, a piping network, mechanical and electrical interlocks to close fire doors and shut down ventilation, directional control valves, installed reserve agent supplies etc. Halogenated agent systems are broadly classified by their method of applying agent to the hazard. The two main types are total flooding and local application system. a. Total Flooding Systems These systems protect enclosed or at least partially enclosed hazards. A sufficient quantity of extinguishing agent is discharged into the enclosure to provide a uniform fire extinguishing concentration of agent throughout the entire enclosure. Halon 1301 by virtue of its lower toxicity, higher volatility, and lower molecular weight, offers particular advantages for use in total flooding systems. b. Local Application Systems As the name implies, these systems discharge extinguishing agent in such a manner that the burning object is surrounded locally by a high concentration of agent to extinguish the fire. In local application system, neither the quantity of agent nor the type or arrangement of discharge nozzles is sufficient to have achieve total flooding of the enclosure containing the object. Often too a local application system is required because the enclosure itself may not be suitable to provide total flooding. Because of its lower volatility, Halon 1211 is well suited for local application systems. The lower volatility plus a high liquid density permit the agent to be sprayed as a liquid and thus propelled into the fire zone to a greater extent than is possible with other gaseous agents.

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6

DESIGN CONSIDERATIONS a. Limitations There are several types of flammable materials on which halogenated agents are ineffective. These are: (1) Fuels that contain their own oxidizing agents such as gun powder, rocket propellants, cellulose nitrate, organic peroxides etc. (2) Reactive metals such as sodium, potassium, NaK eutectic alloy, magnesium, titanium and zirconium. (3) Metal hydrides such as lithium hydride. (4) Chemicals capable of autothermal decomposition, such as organic peroxides and hydrazine. In the first category in which the compound contains its own oxygen supply, often built into the fuel molecule the halogenated agent is unable to penetrate into the reaction zone quickly enough to put out the fire. The oxidizer is in too close physical proximity to the fuel to permit interaction with the extinguishing agent. In the second category, the reactive metals and metal hydrides are too reactive at flame temperatures for the halogenated agent to operate effectively. Also the flame chemistry of metal fires is quite different from that of hydrocarbon fires. A commonly encountered limitation of the capabilities of an agent is its limited effectiveness on deep seated fires at concentrations below ten percent by volume. 1. Safety While both Halon 1301 and Halon 1211 have low vapour toxicity, there are hazards in exposing personnel to high concentrations of either agent (above 10% Halon 1301 or above 4% Halon 1211). Further, the inhalation hazard produced by the fire itself, such as heat, smoke, oxygen depletion and toxic combustion and decomposition products may be substantial. 2. Detection & Actuation The use of automatically actuated systems is important. The primary reason is to limit the size and severity of fire with which the system must deal, thus minimizing decomposition of the agent during extinguishment.

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3. Agent Supply The relatively high cost of agents and the specialised nature of systems using them dictate that a specific supply of agent be provided to protect against a given hazard or set of hazards. Conventionally, the agent is contained in one or more pressurized vessels which are installed near or within the protected area.

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CARBON DIOXIDE SYSTEMS

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1

INTRODUCTION

Carbon dioxide has been used for many years in the extinguishing of flammable liquid fires, gas fires, fires involving electrically energized equipment, and, to a lesser extent, fires in ordinary combustibles such as cellulosic materials CO2 will effectively suppress fires in most combustible materials; exceptions, are a few active metals and metal hydrides, and materials such as cellulose nitrate that contain available oxygen. Further practical limitations of CO2 are related to the method of application and to restrictions imposed by the hazard itself. Carbon dioxide has a number of properties that make it a desirable fire extinguishing agent: It is non combustible, it does not react with most substances, and it provides its own pressure for discharge from the storage container. Also, since carbon dioxide is a gas, it can penetrate and spread to all parts of the fire area. As a gas, or as a finely divided solid called “snow” or “dry ice”, it will not conduct electricity and therefore can be used on energized electrical equipment. It leaves no residue, thus eliminating clean up due to the agent itself. A typical discharge of liquid carbon dioxide has a white cloudy appearance due to finely divided dry ice particles carried along with the flash vapour. Because of the low temperature, some water vapour will condense from the atmosphere, creating additional fog which will persist for a time after a dry ice particles have settled out or sublimed. The cooling effect of the dry ice normally is beneficial in reducing temperatures after a fire. Carbon dioxide gas have a density of one and one-half times the density of air at the same temperature. The cold discharge has a much greater density, which accounts for its ability to replace air above burning surfaces and maintain a smothering atmosphere. Although carbon dioxide is only mildly toxic, it can produce unconsciousness and death when present in fire extinguishing concentrations. The reaction in such cases is more closely related to suffocation than to any toxic effects of the carbon dioxide itself. A concentration of 9% is about most people can withstand without losing consciousness within a few minutes. Breathing a higher concentration of carbon dioxide could render a person helpless almost immediately. 2. APPLICATION SYSTEMS The main component of carbon dioxide system are the carbon dioxide supply, the discharge nozzles and the piping system. These components, along with control valves and other operating devices, dispense the carbon dioxide and provide effective fire extinguishment. Two basic methods are used to apply carbon dioxide in extinguishing fires. One method is to discharge a sufficient amount of the agent into an enclosure to create an __________________________________________________________________________________ 27

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extinguishing atmosphere throughout the enclosed area. This called “total flooding”. The second method is to discharge the agent directly on the burning material without relying on an enclosure to retain the carbon dioxide. This is called “local application”. a

Total Flooding In total flooding systems, carbon dioxide is applied through the nozzles designed and located to develop a uniform concentration of CO2 in all parts of an enclosure. Calculation of the quantity of carbon dioxide required to achieve an extinguishing atmosphere is based upon the volume of the room and the concentration of CO2 required for the combustible materials therein.

b Local Application In local application systems, carbon dioxide is discharged directly on the burning surfaces through nozzles designed for this purpose. The intent is to cover all combustible areas with nozzles located so they will extinguish all flames as quickly as possible. 3. DESIGN CONSIDERATIONS a

Limitations The use of carbon dioxide is limited mostly by its low cooling capacity (particles of dry ice do not “wet” or penetrate) and enclosures incapable of retaining an extinguishing atmosphere. True surface burning fires are extinguished easily because natural cooling takes place quickly. On the other hand, if the fire penetrates below the surface, or under materials that provide thermal insulation that slows down the rate of heat loss (generally referred to as deep seated burnings) a higher concentration of carbon dioxide and a much longer holding time are needed for complete extinguishment. Carbon dioxide is not an effective “extinguishing” agent for fires involving chemicals such as cellulose nitrate that contain their own oxygen supply. Fires involving reactive metals such as sodium, potassium, magnesium, titanium, zirconium, and the metal hydrides cannot be extinguished by carbon dioxide, because the metals and hydrides decompose CO2.

b Life Safety Carbon dioxide should not be used in normally occupied spaces unless arrangements can be made to assure evacuation before discharge. It may be difficult to assure evacuation or if egress is in any way impeded by obstacles or complication passageways. Escape is even more difficult after the discharge starts, because of possible confusion due to noise and greatly reduced visibility.

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c

Methods of Actuation Total flooding and local application carbon dioxide systems normally are designed to operate automatically. The detection device may be any device that are actuated by heat, smoke, flame, flammable vapours, or other abnormal process conditions that could lead to a fire or explosion. Automatically operated systems are required to have an independent means of manual actuation.

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DRY CHEMICAL SYSTEMS

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1

INTRODUCTION

Dry chemical is a powder mixture which is used as a fire extinguishing agent. It is intended for application by means of portable extinguishers, hand hose line systems, or fixed systems. Borax and sodium bicarbonate based dry chemical were the first such agents developed. Sodium bicarbonate become the standard because of its greater effectiveness as a fire extinguishing agent. About 1960, sodium bicarbonate based dry chemical was modified to render it compatible with protein based low expansion foams to permit a dual agent attack. Monoammonium phosphate and potassium chloride based dry chemical then were developed for fire extinguishing use. Shortly thereafter potassium chloride based dry chemical was developed to equal potassium bicarbonate based dry chemical. In the late1960s the British developed urea-potassium bicarbonate based dry chemical. Presently these are the five basic varieties of dry chemical extinguishing agents available. Dry chemical extinguishing systems can be used in these situations where quick extinguishment is desired and where re-ignition sources are not present. Dry chemical are used primarily for flammable liquid fire hazards such as dip tanks, flammable liquid storage rooms, and areas where flammable liquid spills may occur. Systems have been designed for kitchen range hoods, ducts and associated range top hazards such as deep fat fryers. Since dry chemical is electrically non-conductive, extinguishing systems using this agent can be used on electrical equipment that is subject to flammable liquid fires such as oil filled transformers and oil filled circuit breakers. Fire tests on flammable liquids have shown potassium bicarbonate based dry chemical to be more effective than sodium bicarbonate based dry chemical in extinguishment. Similarly, monoammonium phosphate has been found equal to or better than sodium bicarbonate in extinguishment effectiveness. The effectiveness of potassium chloride is about equivalent to potassium bicarbonate, and urea potassium bicarbonate exhibits the greatest effectiveness of all the dry chemicals tested. When introduced directly to the fire area, dry chemical causes the flame to go out almost at once. Smothering, cooling and radiation shielding contribute to the extinguishing efficiency of dry chemical, but studies suggest that a chain-breaking reaction in the flame is the principal cause of extinguishment. 2. APPLICATION SYSTEMS Dry chemical systems are called either engineered or pre-engineered depending upon how the quantity of dry chemical, rate of flow, size and length of piping, and number and size of fittings are determined. An engineered system is one in which individual calculation and design is needed to determine the flow rate, nozzle __________________________________________________________________________________ 31

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pressures, pipe sizes, quantity of dry chemical, and the number, types and placement of nozzles for the hazard being protected. A pre-engineered system, sometimes called a package system, is one in which the size of the system are all predetermined by fire tests for specific sizes and types of hazards. Installation within these limits of hazard and system design assures adequate flow rate, nozzle pressure and pattern coverage without individual calculation. Pre-engineered systems are frequently used for kitchen range and hood fire protection, including deep fat fryers Fixed dry chemical systems consist of a supply of dry chemical, an expellant gas, an actuating method, fixed piping, and nozzles through which dry chemical can be discharges into the hazard area. Fixed dry chemical systems are two types: total flooding and local application. In total flooding, a predetermined amount of dry chemical is discharged through fixed piping and nozzles into an enclosed space or enclosure around the hazard. Total flooding is only applicable when the hazard is totally enclosed or when all openings surrounding a hazard can be closed automatically when the system is discharged. Total flooding can be used only where no re-ignition is anticipated because the extinguishing action is transient. Local application differs from total flooding in that the nozzles are arranged to discharge directly into the fire. Local application is practical in those situations where hazard can be isolated from other hazards so that fire will not spread beyond the area protected, and where the entire hazard can be protected. The principal use of local application system is to protect open tanks of flammable liquids. As with total flooding systems, local application is ineffective unless extinguishment can be immediate and there are no re-ignition sources. 3. DESIGN CONSIDERATIONS a

Limitations

Due to the rapidity with which dry chemical extinguishes flame, dry chemical is used on surface fires involving ordinary combustible materials. However, it should be supplemented by water spray for extinguishing smoldering embers or in case the fire gets beneath the surface. Dry chemical does not produce a lasting inert atmosphere above the surface of a flammable liquid; consequently its use will not result in permanent extinguishment if re-ignition source, such hot metal surfaces or persistent electrical arcing are present. Regular dry chemical will not extinguish fires that penetrate beneath the surface, or fires in materials that supply their own oxygen for combustion. Dry chemical

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mat be incompatible with mechanical (air) foam unless the dry chemical has been specially prepared to be reasonably foam compatible.

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