What is meant by the word foam? Foam is actually hollow spheres of water or bubbles. When water is mixed with air, a foam results, however, it is not stable and collapses quickly. By using Solberg Fire-BrakeTM 3150A Class A Foam Concentrate, it is possible to stabilise bubbles. A foam concentrate will reduce the surface tensions of the water, allowing the bubbles to form more readily. A good foaming agent, such as Solberg Fire-BrakeTM 3150A Class A Foam Concentrate will produce small uniform bubbles. This kind of foam is much more stable than the larger bubbles produced by dish soap type foam concentrates. The small uniform bubbles make a more rigid foam which has a better resistance to heat from a fire, or even the sun. The end result is a foam that will last longer.
By taking a closer look we are able to make some basic calculations on the composition of foam. We know that when a foam is produced, it results in
8 to 12 times the original volume of water (i.e. one litre of water turns into 8 to 12 litres of foam). If we assume an average expansion of ten (half way between 8 and 12) and the foam concentrate is used at a level of 1%, we can state that the foam consists of 90% air, 9.9% water and 0.1% foam concentrate.
How foam works: it can act like a blanket, excluding oxygen and smothering the fire, therefore, disrupting the fire triangle (fuel, heat, oxygen). These characteristics make foam useful for both Class A fuels (common in bushlands) and Class B fuels (associated with forestry equipment).
WHY USE FOAM FOR BUSH FIRES?
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1. Foam expands your water
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2. It clings to fuels
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3. Foam acts like a thermal barrier
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4. A blanket of foam can smother a fire
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5. Foams hold water
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6. Foam slowly releases water
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7. Released water has good wetting characteristics
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8. Foam is white and easily seen
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9. It can be used for ground and aerial tankers
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10. Foam is environmentally safe
Foam also has a cooling effect on the fire. It absorbs heat in two ways - as an insulating material and through the evaporation of water.
How can foam act as an insulating material? As we stated earlier, a foam is 90% air bubbles. This is similar to an insulating foam, therefore, it is capable of absorbing heat from an on-coming fire, keeping the fuel cooler.
Foam can also cool the fire through evaporation. As the foam collapses, water is released. The temperature of the water will rise (absorbing heat) and eventually turn into steam. This is the normal theory for using water on a fire: cooling the fire by removing its energy.
The foam releases its water in two ways. The first method is through heat. When the air in the bubbles heats up it expands, breaking the bubble and releasing its water. The second method of releasing water is due to the effect of gravity. As the foam sits, the bubble wall will no longer be of equal thickness. The water will tend to favour the bottom of the bubble because of gravity. Eventually the bubble will become unstable, releasing its water.
The water released by the foam contains a wetting agent which allows it to penetrate deeper than normal water. By penetrating the fuel deeper, it can increase the water content quickly, therefore, reducing its ability to burn. The "wet water" characteristic is also highly desirable for peat and dense fuel fires.
Since the foam is slowly releasing its water, it is acting like a water reservoir. This, along with the foam's ability to cling to trees, allows the user to control the water. The foam will stick where you put it, while water will run off and form puddles.
When you think of foam, the first image which comes to mind is something that is white, light and fluffy. How could anything of this description be dropped from an aircraft and penetrate the tree canopy? Well, quite simply, it does. When dropped from normal operational heights, the foam is capable of coating the trees and reaching the ground. Relatively speaking, more foam stays in the canopy than would normal water, however, the foam is not trapped in the canopy. The foam will still slowly drain, releasing water. This water will "rain" down from the canopy and increase the relative humidity of the immediate area. The moisture in the air will absorb heat and evaporate, cooling the fire. By increasing the moisture in both the air and the fuel, it is possible to reduce the rate of spread of fire. The deep penetration of the "wet water" from the foam can keep the fuel wet enough to potentially prevent the fire from further advancing.
An interesting advantage to the foam is its colour. The white foam is highly visible to the pilots. Since the foam is easy to see, it will greatly assist the water bombing operations to construct a continuous fire break. As a result, there will be less chance of "weak points" in the fire breaks.
Solberg Fire-BrakeTM 3150A Class A Foam Concentrate can also be an effective agent when used by ground crews. Foam that is applied through hoses has all the same properties as that of aircraft application.
When using foam in bushfire tankers, it is not necessary to have any special equipment. A foam branch produces good foam but it limits your throw, use your standard nozzle to maximise reach of stream. Most foaming will occur when the water stream hits the ground or fuels.
To gain the advantage of foam you only need to put the foam concentrate into your water tank, alternatively, low cost around-the-pump proportioners are now available to introduce the foam concentrate to the water stream, which reduces wasting the concentrate.
A final, yet important, benefit of Solberg Fire-BrakeTM 3150A Class A Foam Concentrate is its safety. A lot of time and effort has been placed in developing a foam concentrate which would be safe for man and environment. A great deal of attention has been given to the effects of aquatic life. Environmental and safety information can be acquired from Solberg Asia Pacific Pty Ltd.