Comparing Water and Fire Retardant in Forest Fire Fighting
When dealing with forest fires, firefighters often have a choice between using plain water and fire retardant. Each has its own advantages and limitations, and understanding their differences can help in making informed decisions. As a rule of thumb, fire retardant is said to be 6 times more effective than plain water in suppressing forest fires. This article will delve into the mechanisms and effectiveness of both water and fire retardant, providing insights into their use in forest fire fighting.
The Mechanism and Effectiveness of Fire Retardant
Fire retardant is not dropped directly onto the fire but rather ahead of it, coating the fuel before the fire reaches it. When the fire eventually encounters the coated fuel, it becomes less likely to ignite, significantly slowing down the spread of the fire. The primary chemical in fire retardant is ammonium phosphates or ammonium sulfates—ingredients that are also found in many home fire extinguishers and even some fertilizers. These chemicals, mixed with a plant-based thickener, create a sticky coating that adheres better to fuels like timber and vegetation. The red color, achieved through iron oxide (rust), serves as a visibility marker for the next pilot to see the extent of the previous drop.
Comparison of Water and Fire Retardant
Water, while effective at cooling and limiting oxygen to the fuel, is more limited in its application due to its physical properties. When water is applied, it either turns into steam or evaporates completely, leaving the fuel exposed once again. In contrast, fire retardant creates a long-lasting coating that continues to have a suppressant effect even after the fire has moved past it.
Another significant advantage of fire retardant is its lower weight. This makes it possible for aircraft to carry a larger amount of suppressant per flight, enabling them to cover more area in a single pass. This efficiency is particularly advantageous during large and spreading fires where it is crucial to maximum coverage in a limited time frame.
Despite these advantages, water remains a viable and widely available resource for fighting small to medium-sized forest fires. In cases where a nearby lake or reservoir is available, planes can perform repeat runs, ensuring sufficient water coverage on the fire. This flexibility makes water a valuable tool in the firefighting arsenal, especially in areas with reliable water sources.
Water vs. Fire Retardant: Cooling the Fuel and Combustion Control
Both water and fire retardant play crucial roles in cooling the fuel and controlling combustion. Water cools the fuel by direct contact and reduces the oxygen supply, temporarily choking off the fire. Fire retardant also chokes off the oxygen supply, but its sticky residue forms a protective coating that can adhere to fuels like timber and vegetation for an extended period. This characteristic of fire retardant means that it doesn't need to be continuously reapplied like water, significantly reducing the amount required to fight a fire of the same size.
Additionally, the artificial foam used in some retardants can adhere to timber better than water, delaying ignition compared to water which can easily evaporate unless a substantial amount is applied directly to the burning material. This makes foam-based retardants particularly effective in forest settings where the surface area of fuel can be vast and varied.
In conclusion, while both water and fire retardant are essential in firefighting, fire retardant offers a more efficient and sustained approach to fire suppression. Its ability to coat and protect fuels, combined with lower weight and better coverage per drop, make it a highly effective tool in combating large and spreading forest fires. However, the availability and flexibility of water ensure that it remains a critical resource in smaller and more localized fires, where immediate cooling and rapid response are paramount.