Firehouse

JAN 2017

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• After arriving, the officer does a 360 with a TIC and identifies the fire room, wind direction and strength, existing and pos- sible flow paths, confirms there are no occupants inside. The fire is on the second floor, ventilation limited, windows intact. • While a crew prepares to make entry, fire- fighters place a ladder next to the window and use a power drill to make a hole. Less than 2 minutes after arrival, the fognail was inserted and fog was applied for 4 minutes (580 psi and 21 gpm). Tempera- tures dropped to less than 329 degrees F (165 degrees C), making it impossible for gases to ignite. Note: Normally the hole would be drilled in the window frame. But the drill used in the experiments was designed for masonry, so the hole was drilled in the wall. Time to complete the hole was approximately 10 seconds. • After applying water through the fog- nail for 4 minutes, water is stopped and a 2-inch handline with a selectable flow nozzle (22–110 gpm, 115 psi) goes in. Crew holds in the stairwell and calls for PPV to clear the structure. First window is opened (Side B) and approach path is cleared; water is applied from the door to the fire room. Later, a window on Side D is taken and the structure is cleared of smoke, and the fire is extinguished. After peaking at 300 seconds, the tem- perature in the fire compartment begins to drop as the fire becomes ventilation- limited. Application of water through the fognail significantly improves thermal conditions. Temperature increases after application of PPV, but followed by quick water inside poses no threat. Conclusions Based on the data recorded on the thermo- couples, video and my experience as the firefighter on the nozzle in this experiment, we came to the following conclusions. In the scenario, we used a significant fire load, with one sofa, approximately 1m 3 wood and particleboard pieces in a stack. There were also combustible linings on the walls and the ceiling, and a wooden floor covered with carpet. This setup cre- ated ventilation-limited conditions, and even though the attack began while the temperatures were not extreme, they were constantly growing and already started posing a threat due to the flammability of smoke and high concentration of unburned hydrocarbons from the pyrolysis process. INTERNATIONAL INNOVATIONS Figure 6: Application of water through the fognail on Side D. Photo by Rafał Własinowicz These conditions may be favorable to create a backdraft or smoke explosion. By cool- ing the smoke, the threats were minimized. Water absorbs energy as it is heated from ambient temperature to its boiling point at 212 degrees F (100 degrees C). However, much more energy is absorbed when water is vaporized from its liquid form into steam. When water is vaporized into steam it expands substantially. How- ever, as energy is removed from the hot fire gases, they are cooled and they contract. This can be explained by the ideal gas law pV-nRT, where p is pressure, V is volume, n is number of moles, R is the gas constant and T is the temperature. However, the sim- ple, no-math explanation is that the volume of a gas varies directly with its temperature (if the thermodynamic temperature of a gas is doubled, the volume will double and if the thermodynamic temperature of a gas is reduced by half, the volume will be reduced by half). It is a bit more complicated, but this illustrates the point. Because it requires much more energy to increase the temperature of water and vaporize it into steam than it does to reduce the temperature of fire gases, water vapor- ized in the hot gas layer will result in a reduction of total volume (contracting the hot gas layer). On the other hand, if you vaporize water on surfaces and do not take energy from the hot gas layer, the tempera- ture of the gases will not be significantly Figure 7: Temperature changes. 400 350 300 250 200 150 100 50 0 0 200 400 600 800 1000 1200 1400 1600 1800 T1 ceiling T2 4 ft. T3 1 ft. T4 plume T5 other FOG FAN t [s] Window 1 Window 2 T [°C] 44 l Firehouse l January 2017

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