Water Mist Replacement for Halon Extinguishers

piss overcast Re smearment for Halon ExtinguishersCHAPTER ONE1.1 IntroductionChoosing the beat assoil inhibition technology is not an easy task. It even guides discussing take chancess and ope dimensionns with insurance companies. The most relevant tending of a gouge natural rubberty aim is the tribute of livelihood which entails the safe evacuation of personnel.The starting point of a overcomeion trunk is a risk analysis to centre the potential concomitant of a bring up. This is fol imprinted by the control of the damage and the reco real effort or emergency response associated with the means of grow suppression adopted.The quality of installation, efficiency and aliment of the suppression system adopted notifynot be over-emphasised.The phase out of halons, due to environmental concerns, has lead to forceful emergence of new release prevention strategies and technologies that ar efficient, as fountainhead as environmentally friendly technologies. rear protect ion halons were phased out of production in development countries due to the quest to regulate the habit of broad(a)s and services of ozone depleting substances(ODS) as reflected in the Montreal Protocol,1987(London Amendment 1990, and Copenhagen amendment1992).Fire suppression federal factors have 2 (2) deadlyological aspects to themThe perniciousness of the federal divisorThe toxicity of upgrade products of the agent.Several new fire suppression systems have been developed very much(prenominal) as inert and halo nose chamberpotdy gaseous systems, peeing fog systems, gas and aerosol generators.Fire has been root outed with weewee since ancient times. Water in the normal configuration is not a suitable suppression medium of all straines of fire. The efficiency of pissing in suppression is enhanced by its procedure of water in form of mists.Survey by Mawhinney and Richardson in 1996 showed that about 50 agencies worldwide ar involved in the research and disc ipline of water fire mist and suppression systems.Water mist in fire suppression does not hold like true gaseous agents and is affect by fire size, the degree of obstruction, ceiling and the ventilation conditions of the compartment. To impressively suppress a fire, a water mist system must generate and behave optimum sized droplets with an adequate.1.2 Objectives and Structure of DissertationThis project aims at studying the water mist as a switch overment for halons systems in the extinguishment of fires. This replacement is a direct consequence of the phase out of halons due to environmental issues and the need to find a drop-in replacement or a suitable alternative in aras where broad(prenominal) level of fire gumshoe is required and the embody of fatalities is too luxuriously.Chapter 22.1 Overview of Fire retrenchmentTo suppress fires, the persona of fire needs to be identified. The class of the fire to be extinguished overly determines the type of fire extinguish er that can be utilize. There argon six (6) types of fires carve up A FIRES These involve inflammable or combustible solids much(prenominal) as wood, rubber, fabric, paper and about plastics.Class B FIRES These atomic number 18 fires involving flammable and combustible liquids or liquefiable solids much(prenominal) as oil, alcohol, petrol, paint and liquefiable waxes.9Class C FIRES These ar fires involving flammable gases such as natural gas, henry, propane, unlessane.9Class D FIRES These are fires involving combustible metals, such as sodium and potassium.9Class E FIRES These are fires involving each of the materials ready in Class A and B fires, but including galvanising appliances, wiring, or opposite electrically energized objects in the vicinity of the fire, with a resultant electrical appal risk if a conductive agent is apply to control the fire.9 http//www.sqa.org.uk/e-learning/FirstLineO2CD/page_06.htmClass F FIRES These fires involve cooking fats and oils, esp ecially in industrial kitchens. The temperature of these fats and oil on fire is much greater than that of another(prenominal) flammable liquids.2.2 Means of Fire SuppressionThe aim of fire suppression is to provide cooling, control the spread of the fire as well as extinguish the fire.The behaviour of a fire is charcterised by the fire triangle which has dismiss, oxygen and instigate as its three places.Combustion process is represented by go + O2 HEAT H2O + CO2 .eqn2.1The electrocution process is an exothermic chemical reaction, involving a fuel and oxygen. The ratio of fuel to transmit must be within the flammability limits of the fuel for combustion to occur. The impoverisheder Flammability Limit (LFL) is the negligible assimilation of fuel vapour in air, bedepression which a consume cannot be supported in the front end of an ignition source.The Upper Flammability Level (UFL) is the uttermost concentration of fuel vapour in air, above which a flame cannot be supporte d. Stoichiometric Mixture is the ratio of fuel in oxygen that requires token(prenominal) energy to support a flame.A branch of the triangle must be removed for the fire to be extinguished. Fires can either be smouldering or flaming combustion. Smoldering occurs when solids such as wood or plastics burn at or on the cake. It usually involves the release of toxic gases and can be difficult to extinguish. Flaming combustion is a gas phase phenomenon that involves the release of visible and infrared radiation. This type of fire generates much more heat.The snuff out of a fire involves either chemical or physical utensils.Physical mechanism Involves the removal of one side of the fire triangle. This can be make by either blanketing the fire (ca exploitation the fuel and air to be separated) or by removing the heat source using an agent with a full(prenominal) heat capacity/ latent heat of vaporization (this depart cool the flame by absorbing the heat). Physical mechanism could be thermal or dilution. thermic physical effect involves adding non-reactive voice gas to a fire pull leading to a reduction in the flame temperature. This is achieved by the distribution of the heat generated to a life-sizedr heat theater. The heat capacity of the introduced agent determines the efficiency of the process. On the other hand, for dilution physical effect, the collision frequence of oxygen molecules with the fuel is lowered when the surplus gas is introduced into the fuel-air mixture. This effect is quite minimal and negligible.Chemical mechanism This is the accustom of an extinguish agent or its humiliation product to disrupt the chain reaction for sustaining combustion. This entails inhibition by halogen portions.Most good suppressants apply both the physical and the chemical mechanisms.The type of hazard associated with an area determines the fire protection system that will be put in place. Halons have been utilised in a wide range of applications. Other al ternatives overwhelmWater Sprinkler Systems This is a very joint type of placed protection that offers safe protection to limit structural damage. The cost of installing water sprinkler systems into alive structures is quite expensive. They are better at protecting structures than its contents 11. The reliability of water sprinkler system has encouraged its wide custom. Accidental dis hitch is uncommon with water sprinkler systems. Water sprinklers have a much lateer response than other systems. They to a fault dumbfound a considerable secondary damage. They cannot be used on live electrical equipment and flammable liquids, but they are used widely in computer and control rooms as well as retentiveness rooms in the USA.Detectors This involves the use of high cutting smoke detection. This is not exactly an active fire protection approach but it serves as an instigator to other fire protection systems 2. speed of light dioxide Carbon dioxide is widely used in gaseous based fi re extinguishing systems. There are two types of carbon dioxide system depending on the fashion by which they are stored. These are high pressure and low pressure carbon dioxide systems. It is a lightheaded agent and has a good penetrating ability. This makes it safe for use on live electrical equipment. They are also used in unoccupied piazzas such as computer and control rooms. Carbon dioxide becomes very minimal direct or secondary damage and allows the installation being put back to immediate use after a fire. It is however toxic and cannot be used in total flooding situations. Carbon dioxide cannot also be used in situations where tip and space are meaningant. High concentrations of carbon dioxide are required for extinguishment and as such they are bulky and heavy. They cannot be used in manned areas because they reduce the oxygen concentration to levels below life support and thus cannot be set in automatic mode. Carbon dioxide systems are generally fast performing and cost effective. Carbon dioxide has also found use in point storage, flammable liquid fires, chemical processing equipment, turbine generators, marine applications, computer rooms and shipboard machinery. sloppy Gases inert gases in use for fire suppression are majorly argon and nitrogen mixtures. These are electrically non-conductive fire suppressants. The mechanism behind their use is the lowering of the oxygen concentration of air to that below the lower flammability point (LFL). They are not liquefied gases and they are bulky because they are stored at high pressure. The concentration of inert gases released in the savage area is high because they have densities that are similar to that of air. Their response time is not very fast and so they are not efficient in situations where the rate of fire spread is high. Inert gases do not decompose thermally and thus they form no breakdown products 2. Inert gases can cause an extreme decrease in the paternity of oxygen in the body acc ompanied by an increase in the concentration of carbon dioxide leading to blemish of consciousness or death and as such health and safety issues have to be considered in its use. Inert gases have found wide credenza because they pose no environmental problems. They are not ozone depleting substances neither do they contribute to planetary warming. They are sedulous in computer and control rooms, record storage, flammable liquid fires and shipboard machinery 2.Halocarbon Gases These are hydrofluorocarbons and perfluorocarbons with zero ozone depleting potentials. They are however greenhouse gases and are governed by the Kyoto communications protocol and hence its release counts towards the national emissions inscription of global warming gases. Halocarbons are electrically non-conductive, are clean agents and are not bulky in harm of space and weight.Foam Systems Foam systems could be low, medium or high expansion systems. Foam systems are efficient for extinguishing liquid po ol fires and large cable fires. In this case, the coruscate acts as a barrier between the fire and the supply of oxygen. The use of chemical dispersants to clean up after its use has special the wide use of foam systems. Furthermore the use of smoke detectors for its activation limits its speed of response. They cannot be used to protect any substance that reacts violently with water. Foams systems are often used with water sprinklers. This increases the efficiency of the systems. Foam systems have found use in the extinguishment of flammable liquid fires, engine compartments and shipboard machinery. juiceless Powder Powders have very high response time for extinguishing fires but have no cooling effect. They thus become ineffective as soon as it settles 2. They are limited in application to extinguishing flammable liquid fires as well as engine spaces.Fine significant Particulates This system is used in combine with halocarbon gases and inert gases 2. They have the advantage of reduced wall and surface liberationes relative to water mist and hint size is easier to control2. They however pose problems to sensitive equipment and cannot be used for explosion suppression applications because they are generated at high temperatures. Fine solid particulates can unless be used in unman areas because of the problems associated with inhalation of particulate substances.Water Mist This employs the use of fine water sprays, usually less than 100 microns in diameter. Water mists can be used on flammable liquid fires, as well as electrical equipment. They are not as effective on small or slow burning fires. Water mist installations pose problems in their design and fabrication.Hybrid Systems Hybrid systems combine one or more of the above fire protection system. A common example of this is the combination of water mist systems and carbon dioxide.There are two orders of applying fire extinguishing agents- constitutional Flooding and Local Application.Total Floodin g They are operated automatically and manually. It entails applying an extinguishing agent to an cover space to achieve a concentration of the extinguisher that is capable of putting out the fire. This method is the most common system of applicationLocal Application The agent is applied today onto the fire plume or the affected enclosure. Portable fire extinguishers are the most common forms of this approach. This method is also known as streaming application.There is an increase in the need for the phasing out of halons and this has brought the search for the staring(a) or drop-in replacement. The department of trade and industry in 1995 listed checklists for the selection of alternatives to halons in critical uses situations asFire scrap effectiveness This involves the speed of fire suppression, the smudge fire hold time, the ability of the alternative to permeate, the elimination of the risk of reignition, the suitability of the alternative to the fire hazard.Ease of induct ive reasoning Ease of maintenance, pipe lam, and cost of installation, cost of refill, floor space and weight, system re-instate time, and availability of the extinguisher.Hazards to occupants Toxicity, noise levels, pressurisation, inhalation, visibility, safety as regards electrical work, thermal rot products 2. burn down effect on equipment water damage, clean up, corrosion, thermal shock.Environmental acceptability Ozone depletion potential, atmospheric lifetime, and global warming potential.Discharge damage This entails clean up of the agent after use, water damage, thermal shock and corrosion.Esso Australia, while looking for alternatives to halons on their installations considered the following issues 14Effectiveness at extinguishing firesEnvironmental effects (a zero ozone depleting and global warming potential) of the agent before use and after thermal decomposition.Toxicity level and a safety margin between its No Observed uncomely Effects Level (NOAEL value) and the ex tinguishing concentration requiredThird party approval from regulatory bodies and safety partners such as International Maritime validation (IMO), NFPA, and EPA or Underwriters laboratory Organisations.Level of applied science required to modify an brisk halon protected installations.Availability as regards to installation and maintenance at a valid cost.2.2 Health and Safety IssuesConsidering the health and safety in the UK, there is no specific regulation as regards choice of fire extinguishing systems. Otherwise fire risks and risk from the use of extinguishment can be categorised down the stairs risks at work. The Management of Health and Safety at Work Regulations 1992 stipulates all risks at work are to be assessed and prevented where ever it is slightly practicable, controlled.In cases where fire extinguishing systems contain toxic substances then the Control of Substances Hazardous to Health Regulations 1988 (COSHH regs) will also apply. The basis of the two regulation s is the prevention preferably than control of the risk.2.3 Environmental regulationsThe International Maritime Organisation (IMO) has prohibited the use of new halon systems from 1994, but accepts the use of existing ones. The EU has inhibitionned its use onboard vessels by the end of 2003.The following are regulations that are put in place to phase out the use of halons.The Montreal protocol on Substances that Deplete the Ozone layer- the Montreal protocol, signed by 25 countries on the 16th of September, 1987 is an international treaty for the control of the production and use of ozone depleting substances. It involves the restriction and eventual barrier of the production, distribution and use of Ozone Depleting Substances. A simulate of this document is attached in concomitant 1.The EC regulations This European legislation was put in place to advertize tighten the restriction on the ban of ozone depleting substances. EC Regulation 3093/94 came into force on the 23rd of De cember 1994. EC Regulation 3093/94 is directly binding in all EU Member States and does not require any national implementing legislation. The new Regulation EC 2037/2000 came into force on 1 October 2000, replacing the Regulation 3093/94. The enforcement requires the use of bodies such as the HM Customs and Excise concerning import of controlled substances. The Department of the Environment proposes to implement these arrangements through enforcement regulations made under both the Environmental security measures play 1990 s.140 and the European Communities Act 1972.(EC REGULATION) The new requirements are applicable to the production, distribution, use and recovery, and control of hazardous substances. The regulations also require the recovery of used controlled substances from certain equipment, such as fire protection systems, for disposal or recycling, during servicing and maintenance procedures of equipment. A copy of the regulation is attached to Appendix 2.The Victorian E nvironment Protection edict for the Control of Ozone Depleting substances (Victorian Government Gazette No.S57, 1990) this piece of legislation depicts the Australian governments shape, reliance and advocacy to the implementation of the Montreal protocol on the phasing out of halon use 14.Environmental Protection agency Under the Clean Air Amendment, the United States Environmental Protection agency, EPA analysed various substances that could substitute fire extinguishing agents that destroy the ozone layer. These substances also have low global warming potential and low Atmospheric lifetime. The SNAP program (Significant New Alternatives Policy) is used by the EPA to replace the use of halons with environmentally friendly systems in the United States. The Clean Air Act was signed into law in 1990. With this Act, the US banned the production and import of new halons 1211, 1301 and 2402 from the 1st of January 1994 in compliance with the Montreal Protocol. The US government also im posed excise tax on halons through specialized training and meet recycling and disposal.Chapter Three Halon SystemsHalon is the generic call up for atomic act 35 contained halogenated hydrocarbons. Halons systems were first installed in the late 1960s and early 1970s.In the gaseous form, halons are excellent fire extinguishers. Halons are mostly employed in situations where fire safety standards are high.Halons are identified by a four digit fall. The numbering system is assigned by the number of carbon, number of fluorine, chlorine and atomic number 35 atoms respectively.Halon 1301, containing carbon, fluorine and atomic number 35 is used in total flooding applications while halon 1211, containing carbon, fluorine, chlorine and bromine is used as hand held movable extinguishers. The two common halon types described are effective in extinguishing classes A, B and C fires. These halons are like because they exhibited high efficiency in suffocating combustion, availability in volume at reasonable cost, high storage stableness, low electrical conductivity, as well as acceptable toxic properties.3.1 Characteristics of HalonsHalons meddle with the chemical reactions which take place during a fire. The properties of halons allow for its use in most situations and thus most of its applications are linked to particular characteristics.These principal applications intromitClean fire fighting agent Halons leave no residue after use. This eliminates secondary damages and holding loss caused by the fire to a minimum 12.Electrically non-conductive This property makes it suitable for safe application on fires involving electrical equipment. It will prevent motion picture of fire fighters to electric shock.Low toxicity This property makes halons acceptable and in most cases halon flooding systems are set in automatic mode by default. They can also be used to extinguish fires while people are present in the protected room. Halon flooding systems do not displace s o much oxygen which can lead to suffocation12Rapid response Halons are effective for rapid knockdown of flames. This property is mostly essential for class B fires involving liquid and liquefiable solids.Low concentration requirement This means low criterion or amount of halons are required for extinguishment. It minimizes weight and space allowance 12.Gaseous state This allows for good penetration and effective extinguishment in confined spaces.Boiling point The boiling point of about -4 allows it to be laid-off (in the case of hand-held extinguishers) as a liquid for a while before it vaporises. This is a key requirement in about manual fire fighting applications.12Low heat of drying up Halons will not condense to form water or ice in halon flooding systems.The most alpha advantage of halons is in its cost effectiveness. Halon fixed systems are the most cost effective of all extinguishing systems.3.2 Extinguishing Mechanisms of HalonsHalons extinguish fires both chemically and physically. chemically they interfere with the chemical reactions that take place during the fire. This characterises halons as inhibitors. Radicals released during combustion to keep the fire burning are suppressed chemically by halons. This reaction is anti-catalytic.When halons are heated during combustion, they produce unload ancestors which cope with those produced by the master copy combustion process 2. Halon 1301 produces bromine radicals which react with hydrogen free radicals to produce hydrogen bromide. The hydrogen bromide then reacts with hydroxyl radical to form water and bromide. The bromide released reacts with the combustion fire again and the whole cycle is repeated.The hydrogen and hydroxyl free radicals produced by combustion are greatly reduced in concentration by combining with the halogen free radicals produced by halons 3.Where RH is the combustible fuel,XBr is a halon agentRH + O2 sinew OH + R .eqn3.1XBr ENERGY Br + Xeqn3.2RH + Br HBr + Reqn3.3HBr + OH H2O + Breqn3.4RH ENERGY R + Heqn3.5H + Br HBreqn3.6The combination of bromine and hydroxyl radical is also an ozone destructive reactionHOBr UV Br + OH..eqn3.7OH + O3 HO2 + O2..eqn3.8Br + O3 BrO + O2eqn3.9BrO + HO2 HOBr + O2 ..eqn3.103.3 HALONS AND THE OZONE3.3.1 The ozone layerThe earth is enclosed by the automatic teller machine. This atmosphere is made up of a mixture of numerous gases in varying proportions. The atmosphere is further subdivided into three regions depending on temperature. These regions are Mesosphere, Stratosphere and Troposphere. The newsworthiness ozone is from a Greek word, ozein, for to smell. It is an allotropic form of oxygen having three atoms in each molecule. It is a pale blue, super poisonous gas with a salubrious odour. 10 In its thickest part in the stratosphere, it is scarcely a trace gas..Ozone is highest in concentration, about 97%, in the stratosphere (15-60 kilometers above the Earths surface) where it absorbs the ultraviolet radiation fro m the sun. Ozone is also highly concentrated at the Earths surface in and around cities. The buildup of ozone on the earths surface in and around cities is a result of industrial activities and is toxic to organisms living at the Earths surface.Table 3.1 shows the percentage volume composition of the constituents of atmospheric air*variable gases http//www.physicalgeography.net/fundamentals/7a.htmlOzone is very reactive and a stronger oxidising agent than oxygen. It is used in ablutionary water, sterilising air, and bleaching certain foods.Ozone is formed when an electric prompt is passed through oxygen. Ozone is prepared commercially by passing cold, dry oxygen through a silent electrical discharge 7.Ozone formed in the atmosphere is from nitrogen oxides and organic gases emitted by automobiles and industrial sources 7. This is achieved by short wavelength ultraviolet. This is actually a health hazard, and it may cause crop damage in some regions. Ultraviolet wavelengths less tha n 200 nanometer reacts with oxygen molecules to make ozone.O2 UV O + Oeqn3.11O + O2 O3 + agitate.eqn3.12The heat released here is absorbed by the atmosphere and results in a rise in temperature of the atmosphere.The structure of ozone has 3 oxygen atoms, but steric hindrance prevents it from forming a triangular structure, with each O atom forming the expected 2 bonds. Instead each atom of oxygen forms only 1 bond, with the remaining negative charge being spread throughout the molecule.7Ozone is very unstable. It is decomposed either by collision with monoatomic oxygen or by ultraviolet radiation on it. The decomposition causes ozone to form oxygen molecules. Heat is also released to the atmosphere by this reactionO + O3 O2 + O2.eqn3.13O3 UV O2 + O + Heat.eqn3.14Ozone is decomposed in the stratosphere to prevent highly bustling ultraviolet radiation from reaching the surface of the earth.3.3.2 Halons and ozone depletionThe ozone layer is mainly depleted by compounds containing chl orine and bromine. Halogens are a chemical family containing fluorine, chlorine, bromine and iodine any carbon compound containing them is known as a halocarbon. While all halogens have the ability to catalyze ozone breakdown, they have an un pit impact on the ozone layer.The quantity of halons released into the atmosphere is small relative to the number of gases present in the atmosphere. Yet they are more active in destroying the ozone or disrupting the ozone balance for two reasonsOzone is in a constant state of imbalance, as it is destroyed and produced by natural processes. This process is controlled by solar input that does not undergo significant fluctuations.The stability of halons makes it transportable from the troposphere to the stratosphere where halogens are made active and broken down very fast, destroying ozone in the stratosphere..The impact is described as depletion potential of the halocarbon. The OZONE DEPLETING POTENTIAL (ODP) is a simple measure of its ability to destroy stratospheric ozone. The ODP of compounds are calculated with reference to the ODP of CFC-11, which is defined to be 1. Thus ODP is a relative measure. A compound withan ODP of 0.2 is, roughly speaking, fifth as bad as CFC-11.The ODP of a compound x is expressed mathematically as the ratio of the total amount of ozone destroyed by a fixed amount of compound x to the amount of ozone destroyed by the same mass of CFC-118Global loss of Ozone due to xODP(x) == ..eqn3.158Global loss of ozone due to CFC-11.The above demeanor depicts that the ODP of CFC-11 is 1.0 by definition. The uncertainties experienced in evaluating the global loss of ozone due to a compound are eliminated here since the mathematical expression is a ratio. Evaluating the ODP of a compound is affected by the followingThe quantity of chlorine or bromine atoms in a molecule.The nature of the halogen, as bromine is a more ozone- destructive accelerator pedal than chlorine.Atmospheric lifetime of the substanc e The atmospheric lifetime of the halon is the time it takes for the global amount of the gas to decay to 36.8% of its original concentration after initial emission. Compounds with low atmospheric lifetimes have lower ODP because it is destroyed in the troposphere.Molecular mass of the substance This is because ODP is evaluated by comparing equal masses and not number of moles.Table3.2 gives time-dependent and steady-state ODPs for some halocarbon in wide use.CompoundFormulaOzone Depletion Potential10yr30yr100yrSteady StateCFC-113CF2ClFCl20.560.620.781.10Carbon tetrachlorideCCl41.251.221.141.08Methyl ChloroformCH3CCl30.750.320.150.12HCFC-22CHF2Cl0.170.120.070.05Halon-1301CF3Br10.4Water Mist Replacement for Halon ExtinguishersWater Mist Replacement for Halon ExtinguishersCHAPTER ONE1.1 IntroductionChoosing the best fire suppression technology is not an easy task. It even involves discussing risks and operations with insurance companies. The most relevant concern of a fire safety engi neer is the protection of life which entails the safe evacuation of personnel.The starting point of a suppression system is a risk analysis to reduce the potential occurrence of a fire. This is followed by the control of the damage and the recovery effort or emergency response associated with the means of fire suppression adopted.The quality of installation, efficiency and maintenance of the suppression system adopted cannot be over-emphasised.The phase out of halons, due to environmental concerns, has lead to forceful development of new fire prevention strategies and technologies that are efficient, as well as environmentally friendly technologies.Fire protection halons were phased out of production in developing countries due to the quest to regulate the use of ozone depleting substances(ODS) as reflected in the Montreal Protocol,1987(London Amendment 1990, and Copenhagen amendment1992).Fire suppression agents have two (2) toxicological aspects to themThe toxicity of the agentThe toxicity of combustion products of the agent.Several new fire suppression systems have been developed such as inert and halocarbon gaseous systems, water mist systems, gas and aerosol generators.Fire has been extinguished with water since ancient times. Water in the normal form is not a suitable suppression medium of all classes of fire. The efficiency of water in suppression is enhanced by its use of water in form of mists.Survey by Mawhinney and Richardson in 1996 showed that about 50 agencies worldwide are involved in the research and development of water fire mist and suppression systems.Water mist in fire suppression does not behave like true gaseous agents and is affected by fire size, the degree of obstruction, ceiling and the ventilation conditions of the compartment. To effectively suppress a fire, a water mist system must generate and deliver optimum sized droplets with an adequate.1.2 Objectives and Structure of DissertationThis project aims at studying the water mist as a replacement for halons systems in the extinguishment of fires. This replacement is a direct consequence of the phase out of halons due to environmental issues and the need to find a drop-in replacement or a suitable alternative in areas where high level of fire safety is required and the cost of fatalities is too high.Chapter 22.1 Overview of Fire SuppressionTo suppress fires, the type of fire needs to be identified. The class of the fire to be extinguished also determines the type of extinguisher that can be used. There are six (6) types of firesClass A FIRES These involve flammable or combustible solids such as wood, rubber, fabric, paper and some plastics.Class B FIRES These are fires involving flammable and combustible liquids or liquefiable solids such as oil, alcohol, petrol, paint and liquefiable waxes.9Class C FIRES These are fires involving flammable gases such as natural gas, hydrogen, propane, butane.9Class D FIRES These are fires involving combustible metals, such as s odium and potassium.9Class E FIRES These are fires involving any of the materials found in Class A and B fires, but including electrical appliances, wiring, or other electrically energized objects in the vicinity of the fire, with a resultant electrical shock risk if a conductive agent is used to control the fire.9 http//www.sqa.org.uk/e-learning/FirstLineO2CD/page_06.htmClass F FIRES These fires involve cooking fats and oils, especially in industrial kitchens. The temperature of these fats and oil on fire is much greater than that of other flammable liquids.2.2 Means of Fire SuppressionThe aim of fire suppression is to provide cooling, control the spread of the fire as well as extinguish the fire.The behaviour of a fire is charcterised by the fire triangle which has fuel, oxygen and heat as its three sides.Combustion process is represented byFuel + O2 HEAT H2O + CO2 .eqn2.1The combustion process is an exothermic reaction, involving a fuel and oxygen. The ratio of fuel to air must b e within the flammability limits of the fuel for combustion to occur. The Lower Flammability Limit (LFL) is the minimum concentration of fuel vapour in air, below which a flame cannot be supported in the presence of an ignition source.The Upper Flammability Level (UFL) is the maximum concentration of fuel vapour in air, above which a flame cannot be supported. Stoichiometric Mixture is the ratio of fuel in oxygen that requires minimal energy to support a flame.A branch of the triangle must be removed for the fire to be extinguished. Fires can either be smoldering or flaming combustion. Smoldering occurs when solids such as wood or plastics burn at or on the surface. It usually involves the release of toxic gases and can be difficult to extinguish. Flaming combustion is a gas phase phenomenon that involves the release of visible and infrared radiation. This type of fire generates much more heat.The extinguishing of a fire involves either chemical or physical mechanisms.Physical mecha nism Involves the removal of one side of the fire triangle. This can be done by either blanketing the fire (causing the fuel and air to be separated) or by removing the heat source using an agent with a high heat capacity/ latent heat of vaporization (this will cool the flame by absorbing the heat). Physical mechanism could be thermal or dilution. Thermal physical effect involves adding non-reactive gas to a fire plume leading to a reduction in the flame temperature. This is achieved by the distribution of the heat generated to a larger heat area. The heat capacity of the introduced agent determines the efficiency of the process. On the other hand, for dilution physical effect, the collision frequency of oxygen molecules with the fuel is lowered when the additional gas is introduced into the fuel-air mixture. This effect is quite minimal and negligible.Chemical mechanism This is the use of an extinguishing agent or its degradation product to disrupt the chain reaction for sustaining combustion. This entails inhibition by halogen atoms.Most good suppressants apply both the physical and the chemical mechanisms.The type of hazard associated with an area determines the fire protection system that will be put in place. Halons have been used in a wide range of applications. Other alternatives includeWater Sprinkler Systems This is a very common type of fixed protection that offers safe protection to limit structural damage. The cost of installing water sprinkler systems into existing structures is quite expensive. They are better at protecting structures than its contents 11. The reliability of water sprinkler system has encouraged its wide use. Accidental discharge is uncommon with water sprinkler systems. Water sprinklers have a much slower response than other systems. They also cause a considerable secondary damage. They cannot be used on live electrical equipment and flammable liquids, but they are used widely in computer and control rooms as well as storage roo ms in the USA.Detectors This involves the use of high sensitive smoke detection. This is not exactly an active fire protection approach but it serves as an initiator to other fire protection systems 2.Carbon dioxide Carbon dioxide is widely used in gaseous based fire extinguishing systems. There are two types of carbon dioxide system depending on the manner by which they are stored. These are high pressure and low pressure carbon dioxide systems. It is a clean agent and has a good penetrating ability. This makes it safe for use on live electrical equipment. They are also used in unoccupied spaces such as computer and control rooms. Carbon dioxide causes very minimal direct or secondary damage and allows the installation being put back to immediate use after a fire. It is however toxic and cannot be used in total flooding situations. Carbon dioxide cannot also be used in situations where weight and space are important. High concentrations of carbon dioxide are required for extinguish ment and as such they are bulky and heavy. They cannot be used in manned areas because they reduce the oxygen concentration to levels below life support and thus cannot be set in automatic mode. Carbon dioxide systems are generally fast acting and cost effective. Carbon dioxide has also found use in record storage, flammable liquid fires, chemical processing equipment, turbine generators, marine applications, computer rooms and shipboard machinery.Inert Gases inert gases in use for fire suppression are majorly argon and nitrogen mixtures. These are electrically non-conductive fire suppressants. The mechanism behind their use is the lowering of the oxygen concentration of air to that below the lower flammability point (LFL). They are not liquefied gases and they are bulky because they are stored at high pressure. The concentration of inert gases released in the hazardous area is high because they have densities that are similar to that of air. Their response time is not very fast and so they are not efficient in situations where the rate of fire spread is high. Inert gases do not decompose thermally and thus they form no breakdown products 2. Inert gases can cause an extreme decrease in the composition of oxygen in the body accompanied by an increase in the concentration of carbon dioxide leading to loss of consciousness or death and as such health and safety issues have to be considered in its use. Inert gases have found wide acceptance because they pose no environmental problems. They are not ozone depleting substances neither do they contribute to global warming. They are employed in computer and control rooms, record storage, flammable liquid fires and shipboard machinery 2.Halocarbon Gases These are hydrofluorocarbons and perfluorocarbons with zero ozone depleting potentials. They are however greenhouse gases and are governed by the Kyoto protocol and hence its release counts towards the national emissions inventory of global warming gases. Halocarbons are electrically non-conductive, are clean agents and are not bulky in terms of space and weight.Foam Systems Foam systems could be low, medium or high expansion systems. Foam systems are efficient for extinguishing liquid pool fires and large cable fires. In this case, the foam acts as a barrier between the fire and the supply of oxygen. The use of chemical dispersants to clean up after its use has limited the wide use of foam systems. Furthermore the use of smoke detectors for its activation limits its speed of response. They cannot be used to protect any substance that reacts violently with water. Foams systems are often used with water sprinklers. This increases the efficiency of the systems. Foam systems have found use in the extinguishment of flammable liquid fires, engine compartments and shipboard machinery.Dry Powder Powders have very high response time for extinguishing fires but have no cooling effect. They thus become ineffective as soon as it settles 2. They are limited in application to extinguishing flammable liquid fires as well as engine spaces.Fine Solid Particulates This system is used in combination with halocarbon gases and inert gases 2. They have the advantage of reduced wall and surface losses relative to water mist and particle size is easier to control2. They however pose problems to sensitive equipment and cannot be used for explosion suppression applications because they are generated at high temperatures. Fine solid particulates can only be used in unmanned areas because of the problems associated with inhalation of particulate substances.Water Mist This employs the use of fine water sprays, usually less than 100 microns in diameter. Water mists can be used on flammable liquid fires, as well as electrical equipment. They are not as effective on small or slow burning fires. Water mist installations pose problems in their design and fabrication.Hybrid Systems Hybrid systems combine one or more of the above fire protection system. A comm on example of this is the combination of water mist systems and carbon dioxide.There are two methods of applying fire extinguishing agents-Total Flooding and Local Application.Total Flooding They are operated automatically and manually. It entails applying an extinguishing agent to an enclosed space to achieve a concentration of the extinguisher that is capable of putting out the fire. This method is the most common system of applicationLocal Application The agent is applied directly onto the fire plume or the affected enclosure. Portable fire extinguishers are the most common forms of this approach. This method is also known as streaming application.There is an increase in the need for the phasing out of halons and this has brought the search for the perfect or drop-in replacement. The department of trade and industry in 1995 listed checklists for the selection of alternatives to halons in critical uses situations asFire fighting effectiveness This involves the speed of fire suppre ssion, the post fire hold time, the ability of the alternative to permeate, the elimination of the risk of reignition, the suitability of the alternative to the fire hazard.Ease of Installation Ease of maintenance, pipe work, and cost of installation, cost of refill, floor space and weight, system re-instate time, and availability of the extinguisher.Hazards to occupants Toxicity, noise levels, pressurisation, inhalation, visibility, safety as regards electrical work, thermal decomposition products 2.Discharge effect on equipment water damage, clean up, corrosion, thermal shock.Environmental acceptability Ozone depletion potential, atmospheric lifetime, and global warming potential.Discharge damage This entails clean up of the agent after use, water damage, thermal shock and corrosion.Esso Australia, while looking for alternatives to halons on their installations considered the following issues 14Effectiveness at extinguishing firesEnvironmental effects (a zero ozone depleting and g lobal warming potential) of the agent before use and after thermal decomposition.Toxicity level and a safety margin between its No Observed Adverse Effects Level (NOAEL value) and the extinguishing concentration requiredThird party approval from regulatory bodies and safety partners such as International Maritime Organisation (IMO), NFPA, and EPA or Underwriters laboratory Organisations.Level of engineering required to modify an existing halon protected installations.Availability as regards to installation and maintenance at a reasonable cost.2.2 Health and Safety IssuesConsidering the health and safety in the UK, there is no specific regulation as regards choice of fire extinguishing systems. Otherwise fire risks and risk from the use of extinguishment can be categorised under risks at work. The Management of Health and Safety at Work Regulations 1992 stipulates all risks at work are to be assessed and prevented where ever it is reasonably practicable, controlled.In cases where fir e extinguishing systems contain toxic substances then the Control of Substances Hazardous to Health Regulations 1988 (COSHH regs) will also apply. The basis of the two regulations is the prevention rather than control of the risk.2.3 Environmental regulationsThe International Maritime Organisation (IMO) has prohibited the use of new halon systems from 1994, but accepts the use of existing ones. The EU has banned its use onboard vessels by the end of 2003.The following are regulations that are put in place to phase out the use of halons.The Montreal protocol on Substances that Deplete the Ozone layer- the Montreal protocol, signed by 25 countries on the 16th of September, 1987 is an international treaty for the control of the production and use of ozone depleting substances. It involves the restriction and eventual prohibition of the production, distribution and use of Ozone Depleting Substances. A copy of this document is attached in Appendix 1.The EC regulations This European legis lation was put in place to further tighten the restriction on the ban of ozone depleting substances. EC Regulation 3093/94 came into force on the 23rd of December 1994. EC Regulation 3093/94 is directly binding in all EU Member States and does not require any national implementing legislation. The new Regulation EC 2037/2000 came into force on 1 October 2000, replacing the Regulation 3093/94. The enforcement requires the use of bodies such as the HM Customs and Excise concerning import of controlled substances. The Department of the Environment proposes to implement these arrangements through enforcement regulations made under both the Environmental Protection Act 1990 s.140 and the European Communities Act 1972.(EC REGULATION) The new requirements are applicable to the production, distribution, use and recovery, and control of hazardous substances. The regulations also require the recovery of used controlled substances from certain equipment, such as fire protection systems, for di sposal or recycling, during servicing and maintenance procedures of equipment. A copy of the regulation is attached to Appendix 2.The Victorian Environment Protection Legislation for the Control of Ozone Depleting substances (Victorian Government Gazette No.S57, 1990) this piece of legislation depicts the Australian governments compliance, reliance and advocacy to the implementation of the Montreal protocol on the phasing out of halon use 14.Environmental Protection agency Under the Clean Air Amendment, the United States Environmental Protection agency, EPA analysed various substances that could substitute fire extinguishing agents that destroy the ozone layer. These substances also have low global warming potential and low Atmospheric lifetime. The SNAP program (Significant New Alternatives Policy) is used by the EPA to replace the use of halons with environmentally friendly systems in the United States. The Clean Air Act was signed into law in 1990. With this Act, the US banned th e production and import of new halons 1211, 1301 and 2402 from the 1st of January 1994 in compliance with the Montreal Protocol. The US government also imposed excise tax on halons through specialized training and proper recycling and disposal.Chapter Three Halon SystemsHalon is the generic name for bromine contained halogenated hydrocarbons. Halons systems were first installed in the late 1960s and early 1970s.In the gaseous form, halons are excellent fire extinguishers. Halons are mostly employed in situations where fire safety standards are high.Halons are identified by a four digit number. The numbering system is assigned by the number of carbon, number of fluorine, chlorine and bromine atoms respectively.Halon 1301, containing carbon, fluorine and bromine is used in total flooding applications while halon 1211, containing carbon, fluorine, chlorine and bromine is used as hand held portable extinguishers. The two common halon types described are effective in extinguishing classe s A, B and C fires. These halons are preferred because they exhibited high efficiency in suffocating combustion, availability in volume at reasonable cost, high storage stability, low electrical conductivity, as well as acceptable toxic properties.3.1 Characteristics of HalonsHalons interfere with the chemical reactions which take place during a fire. The properties of halons allow for its use in most situations and thus most of its applications are linked to particular characteristics.These principal applications includeClean fire fighting agent Halons leave no residue after use. This eliminates secondary damages and keeping loss caused by the fire to a minimum 12.Electrically non-conductive This property makes it suitable for safe application on fires involving electrical equipment. It will prevent exposure of fire fighters to electric shock.Low toxicity This property makes halons acceptable and in most cases halon flooding systems are set in automatic mode by default. They can al so be used to extinguish fires while people are present in the protected room. Halon flooding systems do not displace so much oxygen which can lead to suffocation12Rapid response Halons are effective for rapid knockdown of flames. This property is mostly essential for class B fires involving liquid and liquefiable solids.Low concentration requirement This means low quantity or amount of halons are required for extinguishment. It minimizes weight and space allowance 12.Gaseous state This allows for good penetration and effective extinguishment in confined spaces.Boiling point The boiling point of about -4 allows it to be discharged (in the case of hand-held extinguishers) as a liquid for a while before it vaporises. This is a key requirement in some manual fire fighting applications.12Low heat of vaporisation Halons will not condense to form water or ice in halon flooding systems.The most important advantage of halons is in its cost effectiveness. Halon fixed systems are the most cos t effective of all extinguishing systems.3.2 Extinguishing Mechanisms of HalonsHalons extinguish fires both chemically and physically. Chemically they interfere with the chemical reactions that take place during the fire. This characterises halons as inhibitors. Radicals released during combustion to keep the fire burning are suppressed chemically by halons. This reaction is anti-catalytic.When halons are heated during combustion, they produce free radicals which compete with those produced by the original combustion process 2. Halon 1301 produces bromine radicals which react with hydrogen free radicals to produce hydrogen bromide. The hydrogen bromide then reacts with hydroxyl radical to form water and bromide. The bromide released reacts with the combustion fire again and the whole cycle is repeated.The hydrogen and hydroxyl free radicals produced by combustion are greatly reduced in concentration by combining with the halogen free radicals produced by halons 3.Where RH is the com bustible fuel,XBr is a halon agentRH + O2 ENERGY OH + R .eqn3.1XBr ENERGY Br + Xeqn3.2RH + Br HBr + Reqn3.3HBr + OH H2O + Breqn3.4RH ENERGY R + Heqn3.5H + Br HBreqn3.6The combination of bromine and hydroxyl radical is also an ozone destructive reactionHOBr UV Br + OH..eqn3.7OH + O3 HO2 + O2..eqn3.8Br + O3 BrO + O2eqn3.9BrO + HO2 HOBr + O2 ..eqn3.103.3 HALONS AND THE OZONE3.3.1 The ozone layerThe earth is enclosed by the atmosphere. This atmosphere is made up of a mixture of numerous gases in varying proportions. The atmosphere is further subdivided into three regions depending on temperature. These regions are Mesosphere, Stratosphere and Troposphere. The word ozone is from a Greek word, ozein, for to smell. It is an allotropic form of oxygen having three atoms in each molecule. It is a pale blue, highly poisonous gas with a strong odour. 10 In its thickest part in the stratosphere, it is only a trace gas..Ozone is highest in concentration, about 97%, in the stratosphere (15-60 kilo meters above the Earths surface) where it absorbs the ultraviolet radiation from the sun. Ozone is also highly concentrated at the Earths surface in and around cities. The buildup of ozone on the earths surface in and around cities is a result of industrial activities and is toxic to organisms living at the Earths surface.Table 3.1 shows the percentage volume composition of the constituents of atmospheric air*variable gases http//www.physicalgeography.net/fundamentals/7a.htmlOzone is very reactive and a stronger oxidising agent than oxygen. It is used in purifying water, sterilising air, and bleaching certain foods.Ozone is formed when an electric spark is passed through oxygen. Ozone is prepared commercially by passing cold, dry oxygen through a silent electrical discharge 7.Ozone formed in the atmosphere is from nitrogen oxides and organic gases emitted by automobiles and industrial sources 7. This is achieved by short wavelength ultraviolet. This is actually a health hazard, and it may cause crop damage in some regions. Ultraviolet wavelengths less than 200 nanometer reacts with oxygen molecules to make ozone.O2 UV O + Oeqn3.11O + O2 O3 + Heat.eqn3.12The heat released here is absorbed by the atmosphere and results in a rise in temperature of the atmosphere.The structure of ozone has 3 oxygen atoms, but steric hindrance prevents it from forming a triangular structure, with each O atom forming the expected 2 bonds. Instead each atom of oxygen forms only 1 bond, with the remaining negative charge being spread throughout the molecule.7Ozone is very unstable. It is decomposed either by collision with monoatomic oxygen or by ultraviolet radiation on it. The decomposition causes ozone to form oxygen molecules. Heat is also released to the atmosphere by this reactionO + O3 O2 + O2.eqn3.13O3 UV O2 + O + Heat.eqn3.14Ozone is decomposed in the stratosphere to prevent highly energetic ultraviolet radiation from reaching the surface of the earth.3.3.2 Halons and ozone d epletionThe ozone layer is mainly depleted by compounds containing chlorine and bromine. Halogens are a chemical family containing fluorine, chlorine, bromine and iodine any carbon compound containing them is known as a halocarbon. While all halogens have the ability to catalyze ozone breakdown, they have an unequal impact on the ozone layer.The quantity of halons released into the atmosphere is small relative to the number of gases present in the atmosphere. Yet they are more active in destroying the ozone or disrupting the ozone balance for two reasonsOzone is in a constant state of imbalance, as it is destroyed and produced by natural processes. This process is controlled by solar input that does not undergo significant fluctuations.The stability of halons makes it transportable from the troposphere to the stratosphere where halogens are made active and broken down very fast, destroying ozone in the stratosphere..The impact is described as depletion potential of the halocarbon. T he OZONE DEPLETING POTENTIAL (ODP) is a simple measure of its ability to destroy stratospheric ozone. The ODP of compounds are calculated with reference to the ODP of CFC-11, which is defined to be 1. Thus ODP is a relative measure. A compound withan ODP of 0.2 is, roughly speaking, one-fifth as bad as CFC-11.The ODP of a compound x is expressed mathematically as the ratio of the total amount of ozone destroyed by a fixed amount of compound x to the amount of ozone destroyed by the same mass of CFC-118Global loss of Ozone due to xODP(x) == ..eqn3.158Global loss of ozone due to CFC-11.The above expression depicts that the ODP of CFC-11 is 1.0 by definition. The uncertainties experienced in evaluating the global loss of ozone due to a compound are eliminated here since the mathematical expression is a ratio. Evaluating the ODP of a compound is affected by the followingThe quantity of chlorine or bromine atoms in a molecule.The nature of the halogen, as bromine is a more ozone- destruc tive catalyst than chlorine.Atmospheric lifetime of the substance The atmospheric lifetime of the halon is the time it takes for the global amount of the gas to decay to 36.8% of its original concentration after initial emission. Compounds with low atmospheric lifetimes have lower ODP because it is destroyed in the troposphere.Molecular mass of the substance This is because ODP is evaluated by comparing equal masses and not number of moles.Table3.2 gives time-dependent and steady-state ODPs for some halocarbon in wide use.CompoundFormulaOzone Depletion Potential10yr30yr100yrSteady StateCFC-113CF2ClFCl20.560.620.781.10Carbon tetrachlorideCCl41.251.221.141.08Methyl ChloroformCH3CCl30.750.320.150.12HCFC-22CHF2Cl0.170.120.070.05Halon-1301CF3Br10.4