Assessment of Natural Vertical Ventilation for Smoke and Hot Gas Layer Control in a Residential Scale Structure.

摘要

In firefighting, ventilation tactics are used to increase visibility for firefighter rescue and fire suppression operations, to increase survivability of the occupants of the structure, and to decrease property damage. Improperly implemented ventilation tactics or unplanned, fire-induced ventilation can lead to rapid changes in fire behavior creating fatal conditions inside a building for occupants and firefighters. In this set of experiments, measurements were made within a single, full scale compartment varying the fire size and the ceiling vent conditions between no vents, one 1.2 m by 1.2m (4' by 4') vent, and two combined 1.2 m by 1.2m (4' by 4') vents. The objective was to assess the vents' ability to relieve smoke and the hot gas layer. Thirty-two experiments were conducted using natural gas. These fires were allowed to burn until conditions within the enclosure reached steady state. With one open vent, the hot gas layer was not fully vented. With two open vents, the hot gas layer was fully vented for all three fires sizes.;Simulations of the natural gas experiments were produced using the National Institute of Standards and Technology's Fire Dynamics Simulator in order to explore how well the experiments were simulated based on the same fire sizes and vent conditions. The simulated steady state hot gas layer depths were significantly less than the experimental depths in the doorway when both vents were open, due to a discrepancy in whether or not a hot gas layer existed. The steady state hot gas layer temperatures were significantly under-predicted near the burner when both vents were open (meaning the simulated temperatures were cooler than the measured temperatures) and over-predicted in the doorway when one vent was open and two vents were open (meaning the simulated temperatures were hotter than the measured temperatures). Two additional experiments were conducted using sleeper sofas as fuel, in order to evaluate the differences between controlled natural gas fires and furniture. Neither one open vent nor two open vents was enough to raise the hot gas layer interface height. In the experiment with two sofas, two open vents did reduce the hot gas layer temperature at the doorway by as much as 300 °C (600 °F), but the temperature was still in excess of 200 °C (400 °F). In conclusion, the minimum vertical vent size of one 1.2 m by 1.2m (4' by 4') that firefighters are instructed to use does not remove all hazards, even in a 0.5 MW fire. More discussion is needed in the fire service to define the goals of vertical ventilation and how to best address each goal. More validation of the Fire Dynamics Simulator is needed before vertical ventilation can be accurately simulated in a multi-room structure fire.