OVERVIEW: Vent, Enter, Search (VES) is one of the most talked about tactics in the fire service today. When used correctly, its positive impact can be measured by the lives it saves. The VES method is used either when the location of a trapped occupant is known, or the likelihood for one is high. The firefighter first ventilates an opening, enters the structure, and searches the room that he or she entered. The firefighter then exits via that same opening used to enter and may repeat this procedure for subsequent searches. The purpose of this training article is to describe and quantify the thermal environments that may exist during VES operations and to show the importance of performing this tactic correctly; specifically, the significance of controlling the door of the room that a firefighter enters to search. NIST s Fire Dynamics Simulator (FDS) was used to quantify the thermal environments that may exist in a structure fire when VES is to be performed. Fire Dynamics Simulator (FDS) is a Fortran computer program that solves equations to predict and portray fire growth and thermal environments. A Fortran program reads input parameters specified by the developer of the simulation through the use of a text file. From this input file, FDS computes numerical solutions to various governing equations in order to write the desired output data files. A linked program to FDS, Smokeview, is used to visually portray this data through the use of a menu-driven interface. The footprint of the structure used is 9 m (29.5 ft.) wide by 8.2 m (26.9 ft.) deep. It is a two story structure, with each floor having a height of 2.4 m (7.9 ft.) with a total exterior height of 5.4 m (17.7 ft.) (Figure 1). Figure 1. Structure Used For the Simulations. The first floor consists of the main entry, which has a vaulted ceiling exposed to the second floor, a living room, a dining and kitchen area, a bedroom, laundry room, and an office (Figure 2). Four windows and the front door are located on Side A of the structure, two windows on Side B, two windows and a large sliding glass door on Side C, and three windows on Side D. The middle window on Side D is left open in both simulations. The kitchen on the first floor is the area of origin for the simulations.
Figure 2. First Floor of the Structure. The second floor consists of a loft area above the main entry, a master bedroom suite on Side B, a bathroom on Side D, and another bedroom in the C/D corner (VES Bedroom), which is used as the room for the VES operations in these simulations (Figure 3). Figure 3. Second Floor of the Structure. THE FIRE SCENARIO: The area of origin in these simulations is a stovetop fire in the kitchen on the first floor, designated by a red square (Figure 4). The fire was simulated to start on the stovetop, with a maximum Heat Release Rate (HRR) of 70 kw; according to kitchen fire research conducted by NIST, this would be the expected HRR of a 100 mm (4 in.) pan of corn oil. In these simulations, no windows failed naturally. FirefightingDynamics.com 2012 Page 2
INSTRUMENTATION: Figure 4. Area of Origin. Various instrumentation was included in the models in order to collect data on the thermal environment. Gas phase devices measuring temperature and air velocity on the second floor were included. The gas velocities were measured from floor to ceiling VES bedroom door. These measurement devices were aligned vertically in the middle of the doorway at heights ranging from 0.2 m (0.66 ft.) to 1.6 m (5.25 ft.) above the floor. A thermocouple tree measuring the gas temperature was placed in the VES Bedroom to monitior the temerpatures that firefighters searching that room may encounter. The thermocouples measuring the temperature were located at heights ranging from 0.4 m (1.31 ft.) to 2.4 m (7.87 ft.) above the floor. THE SIMULATIONS: Two separate simulations were conducted to show the difference in the thermal environments by simply controlling the door during VES operations. While both simulations examine the same fire, simulation A portrays incorrect VES operation (failure to close the door upon entry via the window), and simulation B follows correct VES operation (securing the bedroom door after entry via the window). This simple step to VES is taught and fairly well understood, but by how much does closing that door assist firefighter tenability while searching the bedroom? The simulation results visually portray the dramatic difference. The following are constants between the two simulations; the front door opens in both simulations at the 6 minute mark (this simulates the first arriving firefighters forcing entry into the structure), and ventilation of the VES Bedroom occurs at the 8 minute and 30 second mark (simulated by the complete removal of the VES Bedroom s window on Side C). It is important to note that no fire suppression occurs in either simulation; the fire is able to continue to grow uninterrupted by fire extinguishment. FirefightingDynamics.com 2012 Page 3
SIMULATION A - VES Bedroom Door Not Controlled: Simulation A models the fire starting in the first floor kitchen with rapid fire development and an extreme thermal environment throughout the structure. Table 1 documents key events during this simulation. Table 1. Key Fire Events During Simulation A. Event Pot on Stove Ignites Flame Spread To All Upper Cabinets Fire Out Front Door VES Bedroom Window Vented For VES VES Bedroom Untenable For Firefighters Simulation End Time 0 seconds 6 minutes, 0 seconds 6 minutes, 34 seconds 7 minutes, 10 seconds 8 minutes, 30 seconds 9 minutes, 20 seconds 12 minutes, 0 seconds The stove top fire quickly extended to the cabinets above the pan and gradually spread across their surface. The front door to the house opened at 6 minutes and cabinets on both sides of the galley kitchen were soon thereafter on fire and the kitchen was well involved (Figure 5); the fire then progressed towards the front door. The fire in the kitchen area then begins to roll out into the hallway that connects the kitchen to the dining area and first floor bedroom. Extreme thermal conditions were present on the first floor less than 1 minute after firefighter entry via the front door, as seen by flames coming out the front door at the 7 minute 10 second mark (Figure 6). At the point of time when flames extended out the front door, the temperature at the above vaulted ceiling is approximately 600 C (1112 F), with temperatures at the ceiling of the VES Bedroom approaching 200 C (392 F). The VES Bedroom window is vented for the purpose of VES at 8 minutes and 30 seconds, at which point thermal conditions quickly deteriorate on the second floor with the failure to close the bedroom door. By not closing the door, temperatures at the ceiling of the VES bedroom are approaching 450 C (842 F), with temperatures towards the floor above 300 C (572 F) at the end of the simulation (Figure 7). Figure 5. Kitchen Area Well Involved. Figure 6. Flames Out The Front Door. FirefightingDynamics.com 2012 Page 4
Temperature Without Door Control (C) 500 400 300 200 100 0 Window Vented 0 80 160 240 320 400 480 560 640 720 Time (s).04 m.08 m 1.2 m 1.6 m 2.0 m 2.4 m Figure 7. Temperatures in the VES Bedroom Without Door Control. In the above graph, the vertical dotted black line represents when the front door was opened. Fire growth remained relatively stable and contained to the kitchen before the front door was opened. After the door was opened rapid fire growth occurred throughout the first floor until flashover, as seen by the first spike in the graph. The vertical dotted blue line represents ventilation of the VES Bedroom window. This created a flow path for the superheated gases on the first floor to travel up through the vaulted ceiling/loft area and out the VES Bedroom window. By not controlling the door, temperatures throughout the room quickly become unsustainable for firefighters. SIMULATION B - VES Bedroom Door Controlled: The only difference in this simulation is that the VES Bedroom door is controlled shortly after the firefighter enters the window. Table 2 documents key events during this simulation. Table 2. Key Fire Events During Simulation B. Event Pot on Stove Ignites Flame Spread To All Upper Cabinets Fire Out Front Door VES Bedroom Window Vented For VES VES Bedroom Door Closed Simulation End Time 0 seconds 6 minutes 0 seconds 6 minutes 34 seconds 7 minutes 10 seconds 8 minutes 30 seconds 8 minutes 50 seconds 12 minutes The growth of the stove top fire in Simulation B is the same as described in Simulation A VES Bedroom Door Not Controlled ; the thermal environment on the first floor is fairly stable until the front door is opened, at which point the first floor quickly deteriorates until flashover conditions occur. The FirefightingDynamics.com 2012 Page 5
VES Bedroom window is again vented at 8 minutes and 30 seconds, at which point thermal conditions begin to change on the second floor due to the flow path that was created. However, 20 seconds after the removal of the bedroom window, the door to the room is controlled, and thermal conditions in the bedroom subside to sustainable conditions (Figure 8). 600 Temperature With Door Control (C) 500 400 300 200 100 Window Vented Bedroom Door Controlled.04 m.08 m 1.2 m 1.6 m 2.0 m 2.4 m 0 0 80 160 240 320 400 480 560 640 720 Simulation Time (s) Figure 8. Temperatures in the VES Bedroom With Door Control. In the above graph, the vertical dotted black line represents when the front door was opened. Fire growth remained relatively stable and contained to the kitchen before the front door was opened. After the door was opened rapid fire growth occurred throughout the first floor until flashover, as seen by the first spike in the graph. The vertical dotted blue line represents ventilation of the VES Bedroom window. This created a flow path for the superheated gases on the first floor to travel up through the vaulted ceiling/loft area and out the VES Bedroom window. The vertical dotted red line represents the firefighter closing the door of the VES Bedroom 20 seconds after he ventilated the window. This caused an immediate reduction in the room s temperature, which remained below 300 C (572 F) while he searched the bedroom. CONCLUSIONS The use of these two fire models provides quantification and proves the effectiveness of the well-known tactic of controlling the door during Vent, Enter, Search operations. With a fire on the lower floor, and a ventilation opening on an above floor, a flow path is created that causes superheated gases to spread vertically. Without controlling a door, thermal gases have the ability to travel faster towards the ventilation opening. In these simulations, without the VES Bedroom door controlled, flows approached 5 m/s (11 mph); however, if the door is controlled, these air velocities do not occur (Figure 9). FirefightingDynamics.com 2012 Page 6
Average Velocity in Doorway (m/s) 6 5 4 3 2 1 0 Window Vented 0 80 160 240 320 400 480 560 640 720 Simulation Time (s) Without Door Control With Door Control Figure 9. Average Air Velocities in VES Bedroom Doorway. The temperatures firefighters would face at crawling height were also examined. The crawling height of a firefighter was assumed to be 0.8 m (2.6 ft.) for these simulations. NFPA 1971 requires that protective clothing withstand exposure to 260 C (500 F) for five minutes without substantial damage, however other data has indicated that firefighters could survive flashover conditions of 816 C (1500 F) for up to 15 seconds. Per research conducted by NIST, a temperature value of 300 C (572 F) is an appropriate upper limit for a firefighter to remain in the environment for a short period of time. Figure 10 displays the temperatures firefighters endured at crawling height during these two simulations. 400 350 Window Vented Temperature at 0.8 meters (C) 300 250 200 150 100 50 Without Door Control With Door Control Firefighter Tenability 0 0 80 160 240 320 400 480 560 640 720 Simulation Time (s) Figure 10. Temperatures Firefighters Endured at Crawling Height. Without the VES Bedroom door controlled, temperatures at crawling height continue to increase and break the tenability threshold of 300 C (572 F). However, if the door is controlled, temperatures quickly return to more sustainable conditions and allow the firefighter to effectively operate in the room. FirefightingDynamics.com 2012 Page 7
If a door is controlled, thermal conditions should improve. Proving this point was not the intent of these simulations, rather it was to provide a quantified result as to just how these temperatures may vary. The importance of controlling a door is tremendous; temperatures are reduced in these simulations by over 150 C (302 F), a difference enough to greatly increase firefighter tenability while performing search operations. FirefightingDynamics.com hopes you take this information and share it with fellow firefighters to ensure that Everyone Goes Home. Disclaimer: The purpose of this training material is to help educate firefighters across the nation as to thermal conditions that may occur during VES operations. In no way do these values represent the actual temperatures or conditions. Some values used as inputs into the models, such as thermal properties, ignition temperatures, and heat release rates of materials were approximated. Similar materials in an actual structure may have other physical and thermal characteristics. Also, as in any fire, many factors influence fire growth and conditions and may cause the thermal environment to differ. This fire simulation is a scientific tool to assist in quantifying conditions that may exist in this fabricated fire scenario. This fire model has not been validated by a full scale experiment. FirefightingDynamics.com 2012 Page 8