Fire Fighting Engllish

14.1 Fire & Fire Extinguishing The fire is an exothermic reaction evolving a lot of heat (flames), smoke (carbon monoxide) or carbon dioxide + some other products. It can be simulated as follows: ignition Flammable material + air (O2) CO2 + H2O + Heat temperature The evolved heat will further promote the reaction to develop and propagate. Traditionally the fire is simulated on what is called "Fire Triangle". The bad consequences of fires are : 1. Heat: which can burn, melt and destroy. 2. Increase of pressure, which may lead to explosion/mechanical rupture, collapse or decomposition. 3. TOXIC gases (fumes) or smoke. Limits of Flammability The fire reaction takes place with the flammable gas or vapour. For combustible liquids and solids the initiation of flame occurs in the gas phase. Thermal energy (Heat) must first be supplied to convert a sufficient part of the fuel to vapour creating a flammable vapour - air mixture. Solid fuels however must undergo chemical decomposition before vapour is released. The vapour - air mixture has a lower and upper flammable limits as shown in the figure Ignition (Piloted Ignition and Auto Ignition) : Ignition is the process by which self-sustaining combustion is initiated. Piloted ignition can be achieved by the introduction of an ignition source such as flame or spark however if the temperature is raised sufficiently the vapour - air mixture (within the flammable range) will undergo auto ignition in which the onset of combustion is spontaneous. Fire Point : is the lowest temperature of a liquid in an open container at which vapours evolve fast enough to support continuous combustion. Explosion : Generally occurs in situations where the fuel and oxidant have been allowed to mix intimately before ignition. As a result the combustion reaction proceeds very rapidly without being delayed by the need for first mixing fuel and oxidant. If this takes place in a confined space the rapid pressure rise / explosion will cause damage to the container.

Heat Transfer : Conduction : Heat is transferred by direct contact from one body to another. Convection : The heat is transferred by a circulating medium. Radiation : is a form of energy travelling across a space or through materials like air. Sources of Ignition : Open flames like fired furnaces, flares and burn pits, welding, grinding, brazing, metal cutting ...etc. -

Electricity : Sparks of short circuits

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Static electricity

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Internal Combustion engines : Firing mechanism and exhaust

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Self-ignition of certain materials like oily rags.

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NON Explosion proof or intrinsically safe electrical appliances.

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Hot surfaces like pipes of super heated steam ...etc.

Classes of Fires : Class A : Solid carbonaceous materials like wood, fabrics, cotton ...etc. Class B : Flammable liquids like gasoline, diesel, lubricants ...etc. Class C : Flammable gases like methane, ethane, propane, butane ...etc. Class D : Combustible metals Class OF Fire and Suitable Fire Fighting Agent : -

Class A Class B Class C Class D

Water and foam Powder, foam, water for cooling Powder, Halon, CO2 water for cooling Special powder, inert gases like Helium or Argon

Hazardous Areas : This is an area in which a dangerous atmosphere exits: Dangerous areas are classified under 3 headings: Zone 0 : An area in which a dangerous atmosphere could continuously be present. Zone 1 : An area in which a dangerous atmosphere is likely to occur under normal operating condition. Zone 2 : An area in which a dangerous atmosphere is likely to occur under abnormal operating condition.

14.2 Theory of Fire Extinguishing There are basically four ways a fire can be extinguished : 1. Physically separating the combustible substances from the flame. For flammable liquids and gases, this goal can be achieved by isolating the source of leakage (starvation). 2. Removing or diluting the oxygen supply (smothering) using CO2, N2, Steam ...etc. 3. Reducing the temperature of the combustible or of the flame (cooling) using water or foam. 4. Introducing of chemicals that interferes negatively with the combustion reaction and inhibits it (Halons or powder). Fire fighters should use special fire clothes and equipment as deemed necessary : 1. Fire retardant suit to protect the fire fighter from the heat of radiation 2. Fire resistant gloves to protect hands from hot surfaces. 3. Rubber boats as foot protection 4. Fire helmet with face shield to protect head and face. 5. Breathing apparatus to protect respiratory system. Power sources should be isolated and fire fighters should attack the fire with the wind direction to avoid the heat of radiation and smoke. 14.3 Fire Fighting Agents 1.

Water :

Water is very effective fire fighting agent suitable for class A fires and if dispersed i.e. applied in Fog form will reduce the effect of heat resulted from the fire and cool the burning equipment and surrounding, its maximum extinguishing effect is achieved by a combination of mechanisms: Cooling the flame itself generating steam that prevents oxygen access and fog blocking radioactive transfer. When applying water realise the following: Make sure the power supply is disconnected completely. Do not directly poor water onto burning liquids it should be applied in fog for maximum cooling. When water is suitable to contain a certain metal fire it should by applied in a specialised technique. Methods of Water Application :

1. Portable extinguishers 2. Water hoses and nozzles (connected to fire trucks or fire water mains) 3. Fixed and portable water monitors 4. Sprinkler systems 2.

Foam :

The principal application of aqueous foam agents is for fighting flammable liquid fires. Fire fighting foam is a mass of bubbles formed by various methods from aqueous solutions of specially formulated foaming agents. Because foam is much lighter than any flammable liquid it floats on the liquid surface producing an air-excluding, cooling, continuous layer of vapour sealing water - bearing material that can reduce the liquid rate of evaporation and hinder the combustion. Generally the foam is unstable air - water emulsion and can be broken down by: Physical or mechanical forces Heat of the combustion reaction itself Polar chemical

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In general the following criteria for hazardous liquid must be met for a foam to be fully effective : 2.

1. Using the appropriate type and concentration of foam. Foam must be applied with the suitable rate of application and with appropriate configuration. 3. Foam must not be soluble in the liquid to be protected. 4. The liquid must not be water reactive 5. Attention should be given to the possibility of slopover. Types of Foam : 1. Aqueous film-forming foam agents (AFFF) AFFF concentrates contain fluorinated, long - chain synthetic hydrocarbons with particular surface-active properties. They are non-toxic and biodegradable in their diluted form of use. AFFF is suitable for class A and B fires 2. Fluoroprotein foaming agents (FP) In addition to protein polymers, FP contains fluorinated surfaceactive agent, which makes it very effective for in-depth crude petroleum or other hydrocarbon fuel fires. It is also suitable for sub-surface injection tank fires. FP demonstrates better compatibility with dry chemical agents and possesses superior vapour securing and burn back resistance characteristics.

3 and 6% of foam concentrate is available using either fresh or seawater They are also non-toxic and biodegradable after dilution. 3. Film - forming fluoroprotein agents (FFFP) They are composed of protein together with film-forming fluorinated surface-active agent. 4. Protein foaming agents: They contain high - molecular weight natural protein - aceous polymers dried from a chemical digestion and hydrolysis of natural protein solids. They are available for proportioning to a final concentration of either fresh or seawater, they produce dense, viscous foams of high stability, high heat resistance and good resistance to burn back but they are less resistant to breakdown by fuel saturation. 5. Alcohol type foaming agents (AR) They are alcohol resistant concentrates to be applied to spill or in-depth fires of either hydrocarbon or water miscible fuels by any foam generation device. Medium, and High, Expansion Foaming Agents : Medium and high expansion foams are agents for control and extinguishment of class A and some class B fires and are particularly suited as a flooding agent for use in confined spaces. The foam is an aggregation of bubbles, mechanically generated by aspiration or a blower - Fan, which forces air or some other gas through a net or screen that is wetted by an aqueous solution of surfaceactive foaming agents. Under proper conditions firefighting foams of expansion from 20:1 to 1000:1 can be generated. Methods of Application 1) 2) 3)

Portable extinguishers Fire trucks (monitors and guns) Fixed systems

Carbon Dioxide Carbon dioxide (CO2) is used to extinguish flammable liquid and gas fires and fires involving electrically energised equipment and to lesser extent fires in ordinary combustibles such as paper, clothes and other cellulostic materials. Limitations of CO2 as an Extinguishing Agent 1) 2)

Oxygen - containing material and reactive chemicals. Life safety considerations Methods of application

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Portable extinguishers Total flooding systems

Halogenated Agents The halogenated extinguishing agents are known as Halons, they are Halogen (CL, Br or I) derivatives of methane (mainly) or ethane (C2F4Br2). Extinguishing Characteristics : They chemically react with the combustion reaction and hindering the fire process. Application Systems : -

Portable extinguishers Total flooding systems

Limitation : Halon is believed to have a bad effect on Ozone layer and should not be used except on real fire and when lives are exposed to danger. Its use will be ceased as soon as a suitable alternative is obtained. Powder Dry chemical powder are mainly sodium bicarbonate, potassium bicarbonate, potassium chloride, urea potassium bicarbonate, and mono ammonium phosphate. Various additives are mixed with these base materials to improve their storage, flow, and water repellence characteristics Extinguishing Properties : The rapid extinguishing of powder is due to the interference of the dry chemical particles with the propagation of the combustion chain reaction which reduces the concentration of free radicals present within the flames the smothering, cooling and radiation shielding effect of powder is limited. Methods of Application : -

Portable and trolley mounted extinguishers Fire trucks Fixed systems