A Little Fire Science
Page 4 of 12
Water is the most effective fire-suppressing agent known to man. When water is exposed to the flame combustion temperature it vaporizes. The change in phase from a liquid to a vapor under goes a “heat of vaporization” process in which the transition requires the absorption of heat. For a gallon of water to vaporize it must “suck-up” over two million calories of heat. Thus the cooling process. Applied properly one volume of water will cool 300 volumes of burning fuel. But the trick is to do this effectively and not “waste” a lot of water. One is the firefighter technique; his ability to manipulate the hose nozzle to provide a straight-stream, spray or fog as the situation may dictate is essential. Then comes the science. For years it has been the challenge of the scientific community to come up with strategies to enhance the capability of water. The use of additives (agents) to reduce surface tension, increase the surface area and regulate droplet size have been investigated. The problem is to have a f product that is not overly toxic or harmful to the environment easy to use in the field and not cost prohibitive. As such sc products have proven to be satisfactory while others had t< taken off the market.
Water has a surface tension of 73 dynes/cm. CF, like sc foams, can drop that by several factors. This allows the w; molecules to penetrate the fuel more effectively and spread the coverage. There is what is known as fuel limited fire Examples are a burning pile of rubble or a burning pile tires. Tests by the Michelin Tire Company show that CF the deep-seated fire cooling capability needed for fuel-limited situations. Large piles of rubble as a result of post Katrina de up operations have also proven CF unique.
The piles caused spontaneous combustion. Water alone was not efficient putting out the resulting fires. Also very important is its ability to prevent re-ignition of hot spots. The surfactant ingredients in CF go beyond the surface tension reduction by having high affinity for carbon, as demonstrated by the Michelin testing, where tires have a high fraction of carbon. Ingredients in CF provide condensation nuclei to promote droplet formation of the water and increase effectiveness. It is no the breakup of the water droplets to a finer configuration exposes more surface area.
Controlled cooling testing, by Intertek, showed timeline factors of CF versus water in surface/mass cooling comparisons, ranging from 5:1 for glass up to 21:1 for metals. Thus cooling aspect is significant (enhanced by the wetting effect),
During the burning process a chemical chain reaction takes place in which new products form, the key to the reaction that produces fire, an important aspect of the fire tetrahedron (fuel, heat and oxygen are the other aspects). The traditional role for the use of water/agents is to interrupt one or more of these aspects to put out or control the fire. CF goes beyond this relationship as will be discussed.
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The Cold Fire Story FS Testing Post Initial QPL Status The Science Behind Cold Fire ® Addressing Questions From The Field And General Public Favorable Comments From The Field
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