Compressed Air Foam System
Encyclopedia
Fire retardant foam
Fire-fighting foam is a foam used for fire suppression. Its role is to cool the fire and to coat the fuel, preventing its contact with oxygen, resulting in suppression of the combustion. Fire-fighting foam was invented by the Russian engineer and chemist Aleksandr Loran in 1902.The surfactants used...
for the purpose of extinguishing a fire
Fire
Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....
or protecting unburned areas from becoming involved in flame.
Description
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
pumping system that has an entry point where compressed air
Compressed air
Compressed air is air which is kept under a certain pressure, usually greater than that of the atmosphere. In Europe, 10 percent of all electricity used by industry is used to produce compressed air, amounting to 80 terawatt hours consumption per year....
can be added to a foam
Foam
-Definition:A foam is a substance that is formed by trapping gas in a liquid or solid in a divided form, i.e. by forming gas regions inside liquid regions, leading to different kinds of dispersed media...
solution to generate foam. The air compressor also provides energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
, which, gallon for gallon, propels compressed air foam farther than aspirated or standard water nozzle
Nozzle
A nozzle is a device designed to control the direction or characteristics of a fluid flow as it exits an enclosed chamber or pipe via an orifice....
s.
Typical components include a centrifugal pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
, a water source, foam concentrate tanks, a rotary air compressor
Air compressor
An air compressor is a device that converts power into kinetic energy by compressing and pressurizing air, which, on command, can be released in quick bursts...
, a direct-injection foam proportioning system on the discharge side of the pump, a mixing chamber or device, and control systems to ensure the correct mixes of concentrate, water, and air.
It is proven that CAFS attacks all three sides of the fire triangle
Fire triangle
The fire triangle or combustion triangle is a simple model for understanding the ingredients necessary for most fires.The triangle illustrates a fire requires three elements: heat, fuel, and an oxidizing agent . The fire is prevented or extinguished by removing any one of them...
simultaneously. The foam blankets the fuel
Fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...
, thereby reducing the fuel’s capacity to seek out a source of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
. The CAFS solution adheres to ceilings and walls, more readily aiding in rapid reduction in heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
. Also, the opaque surfaces of the foam, as it adheres to walls and ceilings, shield the fuel source from radiant energy
Radiant energy
Radiant energy is the energy of electromagnetic waves. The quantity of radiant energy may be calculated by integrating radiant flux with respect to time and, like all forms of energy, its SI unit is the joule. The term is used particularly when radiation is emitted by a source into the...
. (Brooks, 2005; Brooks, 2006)
CAFS may also refer to any pressurized
Pressurization
Pressurization is the application of pressure in a given situation or environment; and more specifically refers to the process by which atmospheric pressure is maintained in an isolated or semi-isolated atmospheric environment .-See also:* Cabin pressurization* Compressed air* Decompression* Gas...
water style extinguisher that is charged with foam and pressurized with compressed air.
History
The idea that water is not a perfect tool for fire extinguishment has been long noted, as by W. E. Clark (1991), "The process of extinguishing fire by water is cumbersome and generally costly … the cost of installing water mains large enough for required flow, the installation and maintenance of fire hydrantFire hydrant
A fire hydrant , is an active fire protection measure, and a source of water provided in most urban, suburban and rural areas with municipal water service to enable firefighters to tap into the municipal water...
s, and the acquisition and maintenance of fire department pumpers
Fire apparatus
A fire apparatus, fire engine, fire truck, or fire appliance is a vehicle designed to assist in fighting fires by transporting firefighters to the scene and providing them with access to the fire, along with water or other equipment...
, fire hose
Fire hose
A fire hose is a high-pressure hose used to carry water or other fire retardant to a fire to extinguish it. Outdoors, it is attached either to a fire engine or a fire hydrant. Indoors, it can be permanently attached to a building's standpipe or plumbing system...
, and nozzles, make water a fairly expensive extinguishing agent … the use of water is hardly the ideal way to extinguish fire … there must be a better method waiting to be discovered." (p. 75)
Liebson (1996) adds, "Water is an inefficient extinguishing agent. It requires the use of large quantities at costs both financial and physical. These costs are imposed on the firefighter and the community." (p. 5)
The use of foam additives to water for extinguishment dates back to an English patent in 1877 for a method to produce chemical foam (Liebson, 1991, p. xi). The Royal Navy
Royal Navy
The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...
experimented with agents foamed by means of compressed air in the 1930s (Darley, 1994) and the United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...
was using compressed air foam systems (CAFS) in the 1940s for flammable liquid fires. By the 1960s do-it-yourself car washes were using CAFS with low pressure and small-diameter hoses and nozzles, which flowed about 4 gallons (15.1 l) per minute of solution and 4 cubic foot (0.113267388 m³) per minute of compressed air, with a nozzle reach of about 40 feet (12.2 m) (Rochna and Schlobohm, 1992).
In the mid 1970s Mark Cummins, while working for the Texas Forest Service, developed a water expansion system known as the Texas Snow Job. Mr. Cummins invented the CAFS and was issued the US Patent 4318443 in 1982. This pioneering Class A CAFS used dish-washing detergent
Detergent
A detergent is a surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." In common usage, "detergent" refers to alkylbenzenesulfonates, a family of compounds that are similar to soap but are less affected by hard water...
s or a pine
Pine
Pines are trees in the genus Pinus ,in the family Pinaceae. They make up the monotypic subfamily Pinoideae. There are about 115 species of pine, although different authorities accept between 105 and 125 species.-Etymology:...
soap
Soap
In chemistry, soap is a salt of a fatty acid.IUPAC. "" Compendium of Chemical Terminology, 2nd ed. . Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford . XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN...
derivative, which was readily available as waste from local paper
Paper
Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....
manufacturing industries, as a foaming agent mixed as 8 to 9 parts agent to 91 to 92 parts water, flowing up to 30 US gal (113.6 l) per minute. The duration was limited by the use of compressed air cylinders rather than compressors (The US and foreign patent issued to Mark Cummins also included all types of air compressors and inert gas generators). By the mid-1980s, research by the United States Bureau of Land Management in co-operation with Mark Cummins, led to modern design features of rotary air compressors, centrifugal pumps, and direct-injection foam-proportioning systems (Fornell, 1991; IFSTA, 1966). CAFS received national attention in 1988 during the Yellowstone Park wildfire
Wildfire
A wildfire is any uncontrolled fire in combustible vegetation that occurs in the countryside or a wilderness area. Other names such as brush fire, bushfire, forest fire, desert fire, grass fire, hill fire, squirrel fire, vegetation fire, veldfire, and wilkjjofire may be used to describe the same...
s when the four-story Old Faithful Lodge
Old Faithful Lodge
Old Faithful Lodge in Yellowstone National Park is located opposite the more famous Old Faithful Inn, facing Old Faithful geyser. The Lodge was built as a series of detached buildings through 1923 and was consolidated into one complex by architect Gilbert Stanley Underwood in 1926-27...
was successfully protected by blanketing it with compressed air foam (Darley, 1994).
In the spring of 1994, a compressed air foam demonstration vehicle manufactured by W.S. Darley & Co., was driven from coast to coast in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
by Troy Carothers. The purpose was to spread the word about CAFS and display this relatively new technology to United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and Canadian
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
firefighting services. Many years earlier Darley Co. teamed up with Cummins on the WEPS (water expansion pumping system) demonstration vehicle. The 1994 Darley demo vehicle was operated by Troy Carothers who was involved with the initial design and assembly of the Darley AutoCAFS product. Carothers is now the Darley AutoCAFS Manager and oversees all aspects of CAFS development for Darley Co. This demonstration vehicle concept has continued annually since 1994.
Foam types
CAFS is able to deliver a range of useful foam consistencies, labeled from type 1 (very dry) to type 5 (wet), which are controlled by the air-to-solution ratio, and, to a lesser extent, by the concentrate-to-water percentage. Type 1 and 2 foams have long drain times, meaning the bubbles do not burst and give up their water quickly, and long duration. Wet foams, such as type 4 and 5, drain more quickly in the presence of heat .A major advantage of using CAFS is having the unique ability to produce a wide range of foam qualities or foam types to provide the most appropriate foam response to individual fire situations. This gives the fire officer the advantage of custom tailoring the best foam type for the tactical use and fire problem at hand..
After testing a dry type 2 foam in several situations, Johnny Murdock notes, "The emerging consensus is that the dryer foams (type II; maybe type I) should be used to suppress vapors, protect unburned structures, build wildland fire lines involving unburned fuels; … and that structural fire suppression requires a wetter foam (type IV or type V); and that both structural and wildland overhaul require type V foam."
For structural firefighting with compressed air foam, Dominic Colletti recommends utilizing a 0.5 cubic foot (0.0141584235 m³) per minute to 1 US gal (3.8 l) per minute "air to foam solution" ratio, with a 0.5% class A foam proportioning rate. This would produce flow rates from a typical 1-3/4" inch hose of 120 US gal (454.2 l) per minute of foam solution and 60 cu ft (1.7 m³) per minute of compressed air. This air to foam solution ratio produces a wet, quick draining finished foam that will quickly knockdown flame and reduce fire compartment temperature. This ratio also allows for a higher relative foam solution (liquid) flow rate to help maintain the highest levels of firefighter safety possible. (The Compressed Air Foam Systems Handbook, Colletti 2005.)
While Colletti's claims for flows are not agreed upon by many industry experts, as exhibited at the CAFS symposium held in Rosenberg, Texas
Rosenberg, Texas
Rosenberg is a city located in the U.S. state of Texas within Fort Bend County and is part of the Houston–Sugar Land–Baytown metropolitan area. The population was 31,676 at the 2010 census...
in February 2007. A panel there agreed that flows of 1 US gal (3.8 l) per minute foam solution in tandem with 1 cu ft (0.028316847 m³) per minute air produce the most effective blanket. It was further agreed that the maximum combination of air flow mixed with foam solution flow out of a 1-3/4" line under normal pump pressures of 100–125 PSI could not physically exceed a total of 140–150. In other words, the simultaneous flow of 70 cu ft (2 m³) per minute of air and 70 US gal (265 l) per minute of water is approaching the maximum limit or carrying capacity of that diameter hose (1.75 inches). (Texas CAFS Symposium February, 2007)
Water can conversion
Air pressurized waterAir pressurized water
Air pressurized water or APW extinguishers are types of fire extinguishers that extinguish burning material by absorbing heat. They contain of water or water with a wetting agent which is applied by means of a ½-inch hose with a smooth-bore nozzle attached to the tip. They will initially produce a...
(APW) fire extinguisher
Fire extinguisher
A fire extinguisher or extinguisher, flame entinguisher is an active fire protection device used to extinguish or control small fires, often in emergency situations...
s are commonly converted into makeshift CAFS extinguishers by drilling two 1/8-1/16 inch holes in the pickup tube above the water line. The unit is then filled with 1.5 gallons (5.7 l) of water and class A foam, AFFF, FFFP or commercial detergent is added to the water in a 1% ratio for class A fires and a 3%-6% ratio for class B fires. Typically, the tip of the smooth-bore application nozzle is then cut off to allow the foam to properly expand. Keeping the nozzle will result in wetter foam but longer range. Cutting the nozzle will result in an expanded, dry foam but will lack the range of the standard water nozzle. CAFS extinguishers can also be fitted with air aspirators, commonly used on AFFF and FFFP foam extinguishers, which will result in a more expanded foam but will lack the heat resistance of non-aspirated foam, which does not break the bubbles.
Problems
On 17 December 2005 two firefighters from Tübingen, Germany, died inside a burning building when one of the hoses inside the building burst and they were left without extinguishing agent. In the following reconstruction of the tragedy experts were surprised to find out that CAFS filled hoses are more likely to burst under heat because the foam is unable to cool the hoses sufficiently.Some fire district engines have experienced that CAFS filled hoses have a higher incidence of clogging and decrease in pressure.