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The U.S. military is our nation’s most elite group of individuals. They have led our nation to victory in many battles. I do believe, however, none of these victories have come without a precise and thought-out method of attack. Many hours are spent in reconnaissance training to figure out the enemy’s strengths and weaknesses before engaging in battle. A ground war is fought and won, not just with a minimum amount of artillery in hopes that it will be sufficient, but to overwhelm the enemy with the goal in mind never to return.
The fire service is engaged in a war, like it or not, against an enemy that has already invaded our homes and is ready to show itself in a very hostile manner. This enemy is petrochemicals. Your favorite chair, sofa bed or other piece of furniture may seem quite harmless, but its components are killing firefighters in quite a subtle fashion.
The heat release rate (HRR) of these materials is without a doubt catching our brothers and sisters off guard. We cannot be fooled into thinking that these furnishings are just as they appear (like an ordinary piece of furniture), but we need to treat them as highly flammable sources of fuel.
Let’s take a look at the driving force the HRR has on interior structural fires. The HRR is a measurement of heat energy released over a specific unit of time. A fuel has a specific heat of combustion or a total amount of energy released when burned. Different materials possess a given amount of potential energy, such as a bottle rocket with a low potential energy compared to a stick of dynamite. When this energy is released as kinetic energy by the combustion process, it is a concern for us. This energy is measured in kilojoules (kj) per gram. How fast this energy can be released is the heat release rate, which is measured in kj per second.
The potential energy of a synthetic material such as polystyrene yields an energy of 39.58 kj/g, almost identical to propane, which yields 46.45 kj/g. The HRR is an exponential phenomenon, meaning that heat makes more heat. A high HRR directly indicates a high threat to life, rapid temperature changes, faster flashover times and an increase in products of combustion. A single overstuffed chair made out of polystyrene has enough energy to drive a 10-by-10-foot room to flashover. The HRR can be viewed as the engine driving the fire.
Let’s take a look at streams produced from the combination nozzle in comparison to the solid streams produced by the smooth bore. The combination offers you two stream choices. We will start with the discussion of the fog stream.
The 1950s brought about the use of the fog-stream application by Chief Lloyd Layman, who at the time conducted studies based on U.S. Coast Guard and Navy experiments. In these studies, the fog pattern produced great heat-absorption abilities. Two requirements for success with this stream were ceiling temperatures of at least 1,000 degrees Fahrenheit and the fire being attacked must be in a sealed compartment. He also stated that the stream should be remotely injected to ensure no injuries to firefighters from super-heated smoke and stream. This was called the indirect method of attack.
Attacking the fuel source
In none of Layman’s findings did he mention using this technique in an area firefighters or victims would likely occupy. The fog stream has a much larger surface ratio and little, if any part, of the broken stream contacts the solid surfaces or fuel source. Remember, our goal is to apply water to the fuel source and not to just cool off the thermal layer. Many advocates of the combination nozzle state that they prefer this type of nozzle for the versatility to adjust the pattern, narrow or wide. Others also state that they would never actually open up to a fog pattern when they are operating inside due to steam conversion. Then why take the fog nozzle into the structure to start with?