By Anthony Avillo
In addressing and researching the recent scientific information regarding coordinating fireground operations in the modern fire environment, I analyzed the information and put it into terms that make it easier for me to understand and to pass on through my teachings and in the update of the third edition of my book Fireground Strategies.
This is a very exciting time to be in the fire service, whether you are just beginning your career; you are at the doorstep of a promotion; or, like me, you are a veteran (approaching 30 years) who likes to refer to yourself as “seasoned by experience, trial and error, and lessons learned.” Throughout my career, I have tried to stay on the cutting edge and embrace new information as it appears. Although the information in the recent studies is not necessarily new, the science behind it reinforces the need for what we have always seen as safe firefighting operations-the need for coordination between suppression and its brother in support, ventilation activities.
 |
| (1) Smoke and heat are angrier these days because of the high heat release rates that are the foundation of modern living. This building is projectile smoke vomiting! (Photo 1 by Damien Danis; remaining photos by Ron Jeffers.) |
The information provided by the Underwriters Laboratories studies and the Firefighter Safety Research Institute (FSRI), funded by the Federal Emergency Management Agency (FEMA) and the Department of Homeland Security (DHS), regarding heat growth in structures requires us to take a hard look at the way we approach the modern fire environment. The stages of fire growth with which we have become accustomed were applicable to older, legacy contents where the majority of the furnishings were made of natural materials such as wood, cotton batting inside upholstery, cotton curtains, and single-pane windows. Today’s fire environment is much more punishing and lethal in regard to heat buildup and fire dynamics. The synthetic environment of today’s fires as well as the atmospheric sealing qualities of insulation and multiple-pane windows force us to reevaluate the way we approach fires, especially the coordination of ventilation with fire attack (photos 1, 2).
 |
| (2) New buildings are sawdust, glue, and plastic and reach extreme temperatures rapidly. Open windows make it worse. Click to view video |
The studies have found that the modern fire environment has altered the time-temperature curve we thought was relatively linear from ignition through decay. In essence, as modern buildings are more sealed and the fire becomes ventilation-limited, fire often reaches the decay stage earlier, before reaching flashover. This stalled combustion is waiting for oxygen to revive it. When a window breaks or arriving firefighters ventilate, a second, more unforgiving growth stage develops, which leads to flashover and the fully developed fire. Basically, think of it this way: In older legacy occupancies, the fire would use all of the fuel before it used all of the oxygen. In the newer synthetic-rich environment, the fire will use all of the oxygen before it uses all of the fuel. As was stated earlier, it is often the fire department that arrives and adds the oxygen needed to further accelerate burning. Additionally, as Deputy Chief P. J. Norwood of the East Haven (CT) Fire Department points out, any opening, regardless of who or what created it, will provide a flow path. Crews may not immediately recognize some of these flow paths, such as one created when an evacuating resident leaves a door open in the rear or on the sides of the building.
A major reason for taking a hard look at the way we operate is not only that it takes only five minutes for the modern environment to flash over compared with nearly 30 minutes for legacy construction. Much more important (and the catalyst for altered strategies) is the time it takes to reach flashover once ventilation, either by the fire or by the fire department, occurs. The legacy environment took about eight and a half minutes to reach flashover after ventilation; the modern fire environment takes only about two minutes to flash over. This drastically changes our window of opportunity to knock down a fire. In fact, it practically eliminates it!
The nozzle must be ready to put water on the fire while the fire is still ventilation-limited. The key is to starve the fire of oxygen (keep the beast in the cage) until the exact time the water is ready and we are in a position to attack. Opening a door provides ventilation and feeds the fire, which not only influences or creates a flow path but also adds the oxygen the fire is seeking, accelerating the heat release rate given off by the fire. This inflow of oxygen from the open door energizes the fire, increasing the heat release rate significantly.
Flow paths constitute the right-of-way for the products of combustion and are represented by the movement of smoke and heat from areas of high pressure to areas of lower pressure to balance out the environment. They will follow the most efficient path of least resistance unless interrupted by some influence. Flow paths are influenced by building construction, the wind, and other airflow corridors, some of which are inadvertently and incorrectly provided by fire service personnel when they open up before they should. Controlling the flow paths until water is ready to be put on the fire is critical in the modern fire environment. Firefighters caught in the flow paths are in extreme danger. In this environment, the only protection is a charged hoseline-not an uncharged line that is being stretched but a charged line that is ready for battle. That line can help maintain the flow path or, if need be, with proper and timely ventilation, influence the fire back toward its seat.
FLOW PATH ACTIVITY AT A RESIDENTIAL FIRE
A recent fire showed the power of uncontrolled flow path activity and resulted in several firefighters receiving burns; the reflective trim on a probationary firefighter’s turnout coat ignited. The fire was in a two-story, two-family residential dwelling of ordinary construction. The two apartments were completely separated and accessed from side A by two side-by-side doors. One door led to the first-floor apartment; the door immediately adjacent to it led to the second floor. The fire was in the rear on the first floor. Reports indicated that it was venting from the side C window. The building was approximately 40 feet deep. There was also a further report that the fire on the C side was autoexposing the second floor.
An attack line was stretched and the front door was opened, but the door was left open while the attack was being prepared. One of the firefighters told me he could see fire in the rear from the front door. Apparently, there was a delay in getting water to the line. With the door open, the attack team tried to make an advance from the front door toward the rear with an uncharged line. The team was pushed back out by the intense heat that was moving toward the opening they created at the front door. They retreated, but they failed to close the front door while they waited for water. In that time, the fire roared from the rear to the front, causing the gear of the probie, who was on the front steps in immediate proximity to the front door that vented the fire, to ignite. It appears that the open door affected the normal flow path and pulled the fire toward the front door even though the fire was venting out the rear. I thought that maybe horizontal ventilation had been conducted at the front windows before water was on the fire. When I asked, I was told this was not the case.
In addition, the door adjacent to the second floor was forced and apparently left open while companies went in to the search that floor. Two firefighters on the second floor were burned as conditions rapidly deteriorated. It appears that the flow path from the rear window to the front door, which the entry team opened, was not closed and pulled the fire and the products of combustion toward the searching firefighters who were now in the newly created flow path. A firefighter suffered second-degree burns to his legs. The fire was allowed to breathe and seek available oxygen through the opened front door. On the fire floor, although there were no interior doors between the fire and the front door (there was a long hallway off which there were additional rooms), if that front door had been kept closed until water was ready and then controlled until the line was flowing on the fire, this might have been avoided. In both cases on both floors, closed doors would have confined the fire. The mantra should be to keep the beast in the cage until you are ready to do direct battle with it (photo 3).
 |
| (3) The first floor was accessed by the door on the left; the second was accessed by the door on the right. Note the scorch marks around the door and the intense heat damage and scorch marks on the bricks on the A side. |
When ventilation is conducted, whether it is horizontal or vertical, heat moves away from the fire; but even while the heat is moving away, the fire is increasing in energy as it draws oxygen into itself from openings created prior to the application of water. This accelerates the heat release rate and reduces flashover times. Additional openings made in the building also alter the flow path, creating new flow paths and placing firefighters without water [searching, vent-enter-isolate-search (VEIS), and so on] at a more significant risk. This is the reason the first critical action after entering a room for VEIS is to immediately isolate the area by closing the door to the room. Don’t be between the fire and where it wants to go. The window opening, much like the opening of the front door, creates additional flow paths, pulling fire in that direction.
For these reasons and owing to the volatility of the modern fire environment, fire attack actions now require stricter coordination between attack and ventilation. Limiting the air that can get to the fire will limit the fire’s ability to grow and spread. A ventilation-limited fire will also limit the heat-release rate. No longer can we leave doors open while we are waiting for the line to be charged. That only creates more oxygen for the fire to feed on. Remember that forcing a door is horizontal ventilation (about double that of opening a window) and adds fuel (and energy) to the fire. Oxygen introduced by the front door (or whatever opening has been made) can provide the missing link to the ventilation-limited fire. That open door will reduce the time to flashover and subsequent fire travel toward that door (or maybe other areas, depending on the wind direction). In these cases, once the door is forced, pull it closed, limiting the available oxygen until the line is charged and you are ready to attack. A safe attack in the modern environment is based on denying the fire any oxygen until water is ready to be applied, not when water is at the front door with a stretch that must still go 30 feet down the hall. When that type stretch is required, a person should be at the door to control it and feed the charged line in while keeping the door almost all the way closed (open just enough to get the line through).
One of the videos from the study showed two identical fires, side by side. As the door was opened, heavy smoke poured from the doorway. In one structure, the door was left open to simulate a door-open fire attack. The conditions almost immediately got progressively worse, flashing over in less than two minutes, and vented violently through the available roof opening. In the other structure, the attack team controlled the door. There was a significant decrease in the output of smoke and fire growth even with the door partway open (to accommodate a hoseline). The key to fire control prior to water application is to limit the oxygen going toward the fire through the front door (and other openings). Again, as much as possible, keep the beast in the cage!
HORIZONTAL VENTILATION
Horizontal ventilation must be disciplined and communicated properly to the attack team. The longer the stretch, the more disciplined the ventilation operation must be. When a long stretch is needed, ventilation will have to be delayed until the attack team advises that it is in position and ready to put water on the fire. The attack team does not have to be right on top of the fire to attack it. The members just need to be in a safe position from where the reach of the stream can provide cooling. Windows broken or openings made prior to this water application will cause the fire to grow faster and flashover to occur sooner, making areas and buildings more untenable.
Once the line is at the seat of the fire and water is being applied to the fire, we can vent as intended. By putting water on the fire, we have changed the environment from a ventilation-controlled environment to a fuel-controlled environment. If we can create a fuel and heat reduction by putting water on the fire, then the ventilation operation will reduce temperatures and work as it was intended. Without water application, the opening created by firefighters just adds oxygen to the fire, creating more energy and heat output.
Displaying 1/2 Page 1, 2, Next>
View Article as Single page
Fire Engineering Archives
