Foam Extinguishing Systems - Essay Example

Foam Extinguishing Systems FOAM EXTINGUISHING SYSTEMS Foam Extinguishing Systems: Types of systems, uses and considerations for fire suppressionand prevention by fire fighting personnel. Foam Extinguishing Systems 2 Use of foam extinguishing systems for fight and controlling fire is not a new technology, though training and knowledge is required to effectively work with any system that uses foam. In the 1960’s development of Aqueous Film-Forming Foam or AFFF began. By 1979 “the Naval Research Laboratory developed suppressant was in use at more than 90 airports in the U.S. as well as in many civilian fire departments”(NRL.gov). Foam systems can be used in a wide variety of settings and can be fixed or permanent, and utilized through existing, modified, or separate systems. Many, though not all fire departments now use foam to fight fires where flammable Liquids or gases are housed in large quantities. Foams are generally divided into classes, and come in varying levels of expansion from minimal to high. Class A foams are used for typical house fires and other class A fires. Class B foams are used for fires involving flammable liquids. Foam can also be used to a limited extent for class C fires of a gaseous nature. Though foam is very effective if used properly, it requires some knowledge and training to achieve optimal results. This is because the foam must be mixed with water and a certain amount of oxygen for the desired effect. It is the oxygen content that determines the characteristics of the foam and differing effects such as “cooling, suffocating, separating, restraining and displacing”(Marioff). In large fixed extinguishing systems foam is mixed with water, then moved to foam Generators where air is then added. Facilities that typically contain fixed systems are aircraft hangers, oil refineries, laboratories, hazardous material storage and large garages. Foaming agents can also be used in sprinkler, water, and semi-fixed systems which contain predetermined amounts of foam. This type of system is more typical in a multilevel office building, hospital or other business. Though foaming agents can be used with the same equipment or systems used to dispense water, high pressure foam/water guns are used for Foam Extinguishing Systems 3 fighting fires from a safe distance or for preventive cooling, and controlled either manually or electronically with remote control for even more safety. Foam extinguishing systems have many advantages over other systems that use water, dry chemical compounds, or both. Foam has superior flow characteristics, and can “float on liquid surfaces”(Tyco International Ltd.). This means that foam will not be absorbed by flammable agents. It also blankets flammable liquids, preventing exposure to oxygen, which in turn prevents spread of fire. By cutting the fire off from oxygen supply the production of harmful gases is also suppressed. Foam works better as a cooling agent than water as it does not evaporate, and therefore may also be less costly, due to decreased frequency of application and use of manpower. Foam used with other agents also has advantages. Its low surface tension allows water to easily pass through without destroying the entire barrier. The same is true of dry agents used in conjunction with foam. Foam extinguishing systems use various chemical compound as agents, depending on intended use and circumstances. Basic protein concentrates are stable and offer excellent protection against re-ignition. Most commonly they are used in facilities that process or store highly combustible liquids. Fluoroprotein concentrates combine hydrolyzed protein, stabilizing agents, preservatives and hydrocarbon surfactants(adhering agents) to offer protection from fuel contamination. This combination is most often used in refineries and petrochemical plants, according to Tyco International. Synthetic foam agents are mostly hydrocarbon surfactants with high expansion and the ability to cover large surface areas. These compounds are used for large floor surface areas and are most often used in Warehouses, ship cargo holds, and mine shafts. Aqueous film-forming concentrates are a combination of fluorosurfactants and hydrocarbon surfactants. They are the most versatile compounds and used effectively in Foam Extinguishing Systems 4 a variety of systems. Such qualities make AFFF the foam of choice for “fire fighting units, airports and general production facilities”(Tycos ). Another form of AFFF which is alcohol resistant, known as AFFF-ARC, adds a water soluble polymer to aid in extinguishing water soluble fuels like Methanol. Despite its superior ability to control, suppress and prevent fire, foam does have some Disadvantages. Foam is also more difficult and more time consuming, in general, to clean up after use. Foams can also damage electrical systems and wash out lubricants from moving parts. Though foam extinguishing systems generally offer greater protection from physical property as opposed to water, there are some instances in which plain water systems, with alternative methods of operation, may still prove to be more beneficial. An example given by Marioff Hi-Fog is that foam in aircraft hangers often does not reach under the fuselage of aircraft, or does too much damage to working parts when it does reach its intended target. Marioff suggests use of “floor mounted pop-up spray heads” that release a fine mist much like a fogger. Effective use of foaming agents and foam extinguishing systems depends on proper choice of equipment, as well as proper training methods for fire fighting personnel, where outside assistance is required. In a system foam and water are mixed with a device known as a proportioner. There are many types of proportioners and their use is dependent upon the energy supply used and the amount of adjustment required. Balanced pressure systems adapt the “pressure of the foam concentrate with water at the intake of the proportioner” (Tycos). Pressure comes from a pump or from the water supply. Inline systems use the water pressure, constricted in a proportioner, where the foam concentrate is introduced. A disadvantage to this type of system is reduced coverage area. More advanced systems like sprinkler systems in which foam systems are added require installation and maintenance by Foam Extinguishing Systems 5 by certified experts due to their complexity. Because proportioning or control of foam concentrates used by fire departments must often require varying mixtures of concentrate and water, with use of various pressure sources, it is highly recommended by fire suppression experts that all fire fighting personnel receive extensive training in its use. The Fire Science Academy of the University of Reno offers a 32 hour course with training in industrial fire control, study of chemical liquids and gas behavior, and use of water, dry chemical and foam in suppression systems. A class which covers use of high volume foam application stresses use of equipment already in place or easy to obtain for most fire units. It also includes “techniques for calculating the application rate for foam and amount of foam and water required”(FSA). For firefighters responding to a call , the most important factors are the ability to determine if and where hazardous or flammable substances are located, as well as where external and internal pressurized water sources exist.. According to the U.S. Department of Labor, All employers are required to ensure that fixed and portable systems meet OSHA standards. This includes standpipe and hose systems and private hydrants. Fire fighters should become familiar with numerous fixed and portable systems, in order to easily identify them and determine how much, or if additional foam and other resources are needed. Kanterman describes experiments in unconventional use of foam. The first involves a line from a class B truck “attached directly to the fire department sprinkler connection.” The second involved connecting the “foam truck to a 133 ft. building standpipe.” In the first experiment the sprinkler system effectively aspirated the foam to suppress the fire. In the second, the foam quality and performance from the top floor outlet was equal to the ground level. The experiment show the necessity for fire fighters to identify not only various types of foam systems, but also to determine possible alternatives that may save lives property. Foam Extinguishing Systems 6 References Fire Science Academy, University of Nevada. Course overview. Kanterman, R.E. (2001) Abstract. Fire Engineering. H. T. Wilson, 154, 11, 55. Marioff Hi-Fog retrieved 09 December, 2006 from http://www.marioff.com/en/land/ Aircraft/index.htm Naval Research Laboratory. Aqueous Film-Forming Foam Tyco Integrated Systems, Tyco International Ltd. Brochure U.S. Department of Labor, OSHA. Land-side fire protection systems 1915.507 Read More