FIREFIGHTING FOAM In this issue we take an indepth look at firefighting foam. Skillfully considered by Dave Pelton of Solberg WHAT IS FIREFIGHTING FOAM? CLASS “A” FOAM The National Fire Protection Association (NFPA) 11 – Standard Developed in the mid-1980’s, Class A foam was predominately for Low, Medium and High Expansion Foam defines firefighting used for wildland fires but as their popularity grew throughout foam as “…an aggregate of air-filled bubbles formed from an the 1990’s the use of Class A foam was expanded for use on aqueous solution which is lower in density than flammable structural fires. liquids. It is used principally to form a cohesive floating Class A fires consist of ordinary combustible materials, such blanket on flammable and combustible liquids, and prevents as paper, cloth, wood, and plastics. These types of fuels require or extinguishes fire by excluding air and cooling the fuel. It the heat-absorbing (cooling) effects of water or water solutions. also prevents reignition by suppressing formation of flammable Class A fires consist of two types: flaming combustion involving vapours. It has the property of adhering to surfaces, which gases which result from the thermal decomposition of the fuel. provides a degree of exposure protection from adjacent fires.” The second type is deep-seated or glowing. This type represents Or put more simply… foam is used for the suppression of fire combustion within the mass of the fuel and has a slow rate of and can extinguish flammable liquid or combustible liquid fires heat loss and a slow rate of reaction between oxygen and fuel. in four different ways: ■ mop-up: 0.25% ■ separates the flames from the fuel surface ■ initial suppression: 0.5% ■ retards vapour release from the fuel surface ■ fire brake: 0.75% ■ cools the fuel surface and any surrounding metal surfaces ■ protection: 1.0% ■ excludes oxygen from the flammable vapours Note: the minimum admixture rate on other Class A fuel types are 0.1%. HOW IS FOAM MADE? As a synthetic based foam concentrate, Class A foam is Finished foam is a combination of a foam concentrate, water, applied at low concentrations ranging from 0.1% to 1.0%. and air. When these three components are brought together in Cooling and wetting are the primary extinguishing mechanisms. the proper proportions and mixed, foam is produced. The use of Class A foam makes “water wetter” on average To be effective, good foam must contain the correct blend of increasing the effectiveness of water tenfold. physical characteristics: These application rates make the use of Class A foam a cost ■ Knockdown Speed and Flow – this refers to the time effective means of combating fires because smaller amounts required for the foam blanket to spread across a fuel of foam concentrate can be used to make effective foam surface or around obstacles in order to achieve complete and is biodegradable and non-toxic, so it is environmentally extinguishment sustainable. Class A foam is deployed through a variety of ■ Heat Resistance – foam must be able to resist the effects of portable and fixed appliance devices ranging from firefighters’ heat from any remaining fire from the liquid’s flammable backpacks, brush and fire apparatus, to rotary and fixed vapour or heated objects wing aircraft. ■ Fuel Resistance – effective foam minimises fuel pick-up so that the foam does not become saturated and burn ■ Vapour Suppression – a vapour-tight blanket must be capable of suppressing the flammable vapours and minimise the rise of reigniting ■ Alcohol Resistance – foam blankets are more than 90% water. Because of this, foam blankets that are not alcohol resistant will not last very long FOAM CLASSIFICATIONS AND TYPES Each type of firefighting foam has its applications ranging from wildland and structural firefighting to industrial high- hazard, high-risk applications found in Aviation, Chemical, Defence, Energy, Marine, Mining, Oil & Gas, Petrochemical, Pharmaceutical, Pipeline and Solvents & Coatings industries. Firefighting foams are divided into two classifications Class A and Class B. Technicians Conduct a Foam Burn-back Test 62 FIRE MIDDLE EAST | DEC 2013/JAN 2014 are susceptible to fuel pickup, therefore, care should be taken to minimise the foam and fuel from submerging. SYNTHETIC FOAMS This type of foam concentrate is based on a mixture of surfactants and solvents, both fluorinated and fluorosurfactant / fluoropolymer-free. These types of foam concentrates may or may not form films or membranes on the fuel surface, depending on the foam concentrate and the fuel being protected. FLUOROPROTEIN FOAMS Fluoroprotein foams are a derivative of protein foams. Fluoroprotein foams have fluorochemical surfactants added. They are intended for use on hydrocarbon fuels and selected oxygenated fuels. They must be properly aspirated and should not be used with non-air aspirating fog nozzles. WHY USE FOAM? Class B fires consist of flammable or combustible gases, and liquids. Extinguishment is normally accomplished by excluding (eliminating) oxygen, interrupting the combustion of the chain Class A Foam Mop-up Use Wild-land reaction, or stopping the release of the combustible vapours. As we look to the future, the use of and application for The type of Class B hazards are either water soluble (meaning Class A foam will certainly advance technologically. A current they mix with water) e.g. polar solvents or water insoluble example to point to is the recent generations of nozzle-aspirated (meaning they will not mix with water) e.g. hydrocarbons. For induction systems and Compress Air Foam Systems (CAFS) have water soluble fuels, special alcohol resistant foam agents that been more reliable than earlier generation models. will not mix with the fuel are required. Many different extinguishing agents are effective on CLASS “B” FOAM flammable or combustible liquids. However, foam is the There are several types of available Class B foams. Each foam only extinguishing agent capable of suppressing vapours concentrate is developed for a specific application. Some and providing visible proof of securement. Reasons to use firefighting foams are thick and form a heavy, heat-resistant firefighting foam include: covering over a burning liquid surface. Other types of foams are ■ fire prevention – application of a foam blanket on an thinner and because of that, they will spread much more quickly unignited spill over the fuel surface. Still, other types of foams will generate a ■ vapour suppression – prevention of vapours from finding an vapour sealing film on the surface of the fuel. Additional foam ignition source concentrate types, such as medium and high expansion foams, ■ odour control – suppression of hazardous or noxious can be used in applications requiring large volumes to flood vapours surfaces and fill cavities within the hazard. ■ personnel exposure – protection of fire and/or rescue personnel during emergency operations CHEMICAL FOAMS ■ asset protection – pre and post security of the hazard until These foams are produced by the chemical reaction which securement or removal is conducted occurs when the two chemicals, aluminum sulfate and sodium Class B foam is not effective on all types of fires. It is critical bicarbonate are mixed together. The energy required to create to know the type of fire and fuel involved. Firefighting foam is the foam bubbles comes from this reaction between the two not effective on: Class C Fires (energised electrical equipment) chemicals. This type of foam is obsolete. as water conducts electricity and foam contains 90% plus water. Class C fires can be extinguished by either de-energising PROTEIN FOAMS the equipment or using alternative extinguishing media such Protein foams are manufactured with naturally-occurring as dry chemical, carbon dioxide or a clean agent; Pressurised sources of protein, such as hoof and horn meal or feather meal. Gases – materials stored as liquids but are vapourous at ambient They are intended for use on hydrocarbon fuels only. Foams temperature. The vapour pressure for these type fuels is too made from protein foam concentrates usually have a good heat high for foam to be effective; Three-dimensional Fires – in which stability and resist burnback. They must be properly aspirated the flammable liquid is being discharged from an elevated source and should not be used with non-air aspirating fog nozzles. creating a pool fire on a lower surface area; Class D Fires – These foams are generally not as mobile or fluid on the fuel combustible metals such as aluminum, magnesium, potassium, surface as other types of low expansion foams. Protein foams sodium and titanium alloys. The extinguishment of Class D metals requires the use of specialised dry powder agents. FIRE MIDDLE EAST | DEC 2013/JAN 2014 63 EVOLUTION OF CLASS B FIREFIGHTING FOAMS Firefighting foams have been used for the extinguishment of fire for almost 100 years in various guises starting with chemical foams, and at each of the advancement steps along the way, performance and safety of those agents improved on the prior foam concentrate type. CHEMICAL PROTEIN SYNTHETICS FLUOROPROTEINS ENVIRONMENT SAFE 1915–1933 1933 1963 1965 FOAMS 2005 Early 1900s – the first 1930s – Protein foams were 1960s – Synthetics (AFFF Mid-1960s – Fluorprotein 2005/Present – as firefighting foams were a major improvement. They and AR-AFFF) entered the foam was introduced after environmental regulations chemical foams. They were chemically stable and market. They have the the synthetics, mainly as on fluorinated synthetic functioned by a chemical effective on Class B fires and ability to readily spread a market response by the foam concentrates increase reaction from mixing two at the time quickly became over a fuel surface, are very protein foam manufacturers. around the world, a new or more chemicals at the the industry standard. Their forgiving during a fire, they Adding fluorosurfactant generation of environment time of use, which created major drawback was limited can be discharged through to standard protein foams friendly foam concentrates the foaming.