Often for firefighters to accept change, a specific need has to be acknowledged. Sometimes this need is nothing more than asking if there is a better way of doing something. However, change also may occur when the practical application of equipment or theory results in unexpected positive outcomes. This is the case with positive-pressure attack, a necessary change that addresses how we attack today's structure fires.
Used appropriately, PPA improves our ability to provide firefighting services and increase firefighter safety. Used inappropriately, PPA can cause unsafe conditions that may injure firefighters and increase property damage. PPA is no different from any other innovative change; it has been and should be approached with varying levels of caution.
Will blowing fresh air into a burning structure push fire throughout the building?
No. The air moves from the ventilation point to the exhaust point as it seeks an area of lower pressure. During a fire the slight increase in pressure to the interior of the structure will ensure the fire remains burning toward the area of negative pressure outside of the building.
Will PPA push fire throughout voids in the building?
No. Fire reacts to pressure differentials. It will move from an area of high pressure to an area of lower pressure. If the pressure remains constant in the void, PPA won't push fire into it. If the void has not been opened, such as cutting a hole in a roof, PPA will not cause fire to be appreciably pushed into that space.
Will PPA spread fire into voids of a balloon frame — constructed building?
No. Live burn field tests have been conducted with an attempt to push fire into non — fire-stopped stud, joist and rafter spaces. The only instance in which fire was dramatically pushed into these spaces was when the roof was opened and the fire now had an area of negative pressure to move into.
Why does PPA sometimes make the fire appear to intensify at the exhaust point?
As heat and products of combustion leave the exhaust point, they're forced to move out of a relatively small opening under pressure. They also come into contact with outside air that may support ignition because temperature, pressure and oxygen have reached optimal levels. When PPA is used correctly, the conditions observed at the exhaust point are not occurring in the interior, where the environment is improving.
Does PPA require additional staffing to accomplish the fire attack?
With proper training, fire crews can accomplish PPA in the same time it takes to attack a fire without the benefit of coordinated ventilation.
Does PPA delay rescue and fire control?
It takes no additional time for crews to take the blower with them toward the structure if they do so when they first leave the apparatus. The key element is that crews must take the blower as they begin the fire attack to avoid an additional trip back to the apparatus. Experience shows that fire attack will begin without the benefit of ventilation if the blower is left behind on the apparatus.
What if you're uncertain whether there are trapped victims between the fire and the exhaust opening?
The best chance that trapped victims have for survival is immediate ventilation by attack crews, limiting victim exposure to lethal heat and products of combustion. The first-arriving officer must ensure there are no victims awaiting rescue at the exhaust opening during the initial fire and exhaust point size-up. Victims who are at openings must be rescued prior to starting pressurization.
What are the best locations for the ventilation and exhaust openings?
The ventilation opening is where the blower is going to be positioned and operated. For safety, this also must be the same opening fire crews enter to begin their attack. This is comparable to fighting a wildland fire from a safe anchor point. The attack entrance, where the blower is positioned, becomes the anchor point. The exhaust opening is where the heat and smoke will leave the structure and should be as close to the fire area as possible. This may be a window, door or gable opening. Think of it as the blower pushing the first crew into the structure as the heat and toxic products of combustion are removed ahead of them to the exterior of the building.
Can a crew make an exhaust opening in the wrong location?
No. There are only more effective locations for exhaust openings. There may be times when the layout of a structure may preclude the first exhaust opening from being the most effective. Opening another window from the exterior or opening a door from the interior may remedy this. If interior crews are in the building before the blower is started, they must leave to the outside and reenter only after the blower is operating. This will prevent them from being in a potentially dangerous position. Regardless of the location, removing toxic products of combustion that impede fire attack crews will have positive outcomes.
At what point during PPA should the blower begin pressurizing the structure?
After ensuring that an adequate and ample exhaust opening has been made, the blower may then be directed into the structure. For optimum PPA, the air stream should be directed inside 10 seconds before attack crews enter with a charged line. Experience has shown that a knockdown of the fire within five to seven minutes is essential to avoid being trapped inside a structurally compromised building.
Is it dangerous to put the blower too close to the seat of the fire?
We have conducted many live fire burns in which the fire was started adjacent to where the attack was going to be initiated. These tests verified that fire would not be blown throughout the structure. The fire appears to intensify or burn cleaner momentarily but decreases as the atmosphere begins to cool. This decrease in size also has been observed when the blower is placed near the main body of the fire. The blower should not be turned into the structure without a charged line in place and an adequate and ample exhaust opening ensured.
What about the carbon monoxide introduced by the gasoline-powered blowers?
The top priority of any initial fire attack is to rescue victims who are endangered by toxic products of combustion or trapped by fire. Blowers will drop the co levels in a structure fire from 1,200ppm to a survivable level near 100ppm. In other words, the co introduced by the blower is negligible when compared to the deadly levels produced in a structure fire.
When should firefighters use PPA?
Firefighters should consider using PPA in any free-burning structure fire. When heat and products of combustion are where you don't want them, pressurization will force them out and result in a safer, more tenable interior.
What about using PPA to fight attic fires?
Setting up a blower and pressurizing the living, office or work area in coordination with the fire attack will provide a tenable atmosphere and confine the fire to the attic space.
If the space below isn't heavily charged with smoke when interior crews start operations, no exhaust opening on that floor should be made. This maintains the highest possible pressure in the area below the attic space, forcing heat and smoke to be primarily contained in the fire area. Crews in the pressurized space below can make small inspection holes into the attic to determine the extent of fire involvement as they attack the fire from below.
What about using PPA to fight basement fires?
A stubborn basement fire is undoubtedly one of the more difficult challenges firefighters will face. Two major problems with fires below grade are the lack of access and the difficult task of effective ventilation, which combine to increase the levels of heat and products of combustion. PPA is an excellent option for these types of fires, especially if there are existing exhaust openings such as basement windows. The blower positioned on the floor above the basement must overcome the natural tendency of heat and smoke to rise as it redirects these products out the exhaust opening.
What if a room, basement or building has only one opening?
Pressurization is still an option when you have to ventilate a space that has only one door opening and no windows. The blower can be placed at the opening with the air entering the lower part of the door. The exhausting heat and smoke will flow out at the top of the opening. PPA may be limited in this application because the firefighter's entry point, the ventilation opening and the exhaust opening are all the same door. This may create a hazardous condition for both firefighters and victims because most standard doors aren't large enough to provide adequate ventilation and exhaust openings.
An adequate exhaust opening is just as important as the ventilation opening. Without an adequate exhaust, crews run the risk of intensifying the fire much like how a convection oven works. In cases such as this, blowers shouldn't be used until the fire is knocked down.
What are some potential problems with PPA?
Although PPA is an excellent mechanism to achieve a coordinated fire attack, there are situations that may present a problem. The major precautions include: inadequate exhaust openings, backdraft, noise, hidden fire, inadequate understanding and/or lack of proper training.
Exhaust opening. Exhaust openings must be large enough to remove products of combustion from the building. Without adequate-sized exhaust openings, the interior environment can become unstable and redirected toward interior crews if a separate exhaust opening occurs behind them. If products of combustion appear to be exiting under great force, create additional exhaust openings on the fire side of the structure.
Backdraft. Accepted practice for backdraft conditions is to ventilate at a high point before fire crews enter the structure at a low point. PPA may not be an option for conditions that have a backdraft potential. A structure with signs of backdraft suggests that there is no life or property value remaining. It's important to remember that if flame can be seen in a structure, a backdraft is very unlikely.
Noise. The noise from a gasoline-powered blower can be a problem or a benefit. The loudest noise is directly at the blower and diminishes as the fire crew enters the structure. The benefit is that interior crews know that ventilation is in place by the noise of the blowers. Crews also could find their way out by moving toward the noise if they become disoriented or lost.
Hidden fire. After the fire is knocked down, the blowers may create a deceivingly clear atmosphere because they're exhausting the heat and smoke that would indicate a hidden fire. Crews should turn off the blower for 10 minutes and then observe the interior conditions to ensure that overhaul is satisfactory.
Inadequate understanding and lack of proper training. This last problem is a very important one. PPA may appear to be a simple operation — set up a blower and advance a hose line. Not very complex, but there's far more to it than that. As with any other tactic, PPA must be well understood and regularly practiced by firefighters before it can become an effective and safe method for fire control.
Under what circumstances is PPA not advised?
There are four situations where PPA should not be used:
When firefighters or victims are standing at windows or other openings that could become an exhaust opening when the blower is started.
When fire crews are operating in a location that places them between the fire and an exhaust opening. The incident commander must ensure that this doesn't occur. This an absolute rule. To avoid this situation, always start ventilation before entering.
When there's combustible dust or flammable vapor in the atmosphere. Fires in grain elevators or other occupancies at risk of dust explosions should be controlled using a tactic least likely to increase suspended dust. This may be through the judicious application of water, possibly by misting the area. Don't move any combustible atmosphere to a possible ignition source.
When backdraft conditions exist. Any structure exhibiting signs of a possible backdraft must be ventilated at a high point before fresh air is introduced at a low point. Fires that have progressed to the smoldering stage leave little hope of rescuing viable victims.
Can positive pressure protect exposures?
Yes. Pressurizing the interior of a structure makes it more difficult for fire and smoke to enter it. Pressurization can provide an excellent means of protection for buildings or other areas exposed to adjacent fires. This method works whether the exposure is an entire structure or a partitioned area in the same structure, such as a business in a strip mall, a home with an attached garage, or a single floor in a high-rise. Under these conditions it's not necessary to make an exhaust opening as we are attempting to create the highest possible pressure within the exposure to keep heat, smoke and fire out.
What size building can a blower ventilate?
After more than a decade of evaluating pressurization under live fire conditions and using positive pressure regularly at incidents, it's safe to say that a single 20,000cfm-rated blower can effectively ventilate buildings up to 5,000 square feet. The exiting volume is what's important.
Safe & effective
PPA is a safer and more effective option over other means of ventilation for the following reasons:
Safety. PPA is a simple, rapid operation that generally takes place outside and at ground level. Vertical ventilation requires ladders to access a roof that may rapidly become structurally unsound under fire conditions. It requires multiple tasks that are mutually dependent for the procedure to be successful.
Effectiveness. PPA confines the fire by using exhaust openings near the fire. The fire may have self-vented adequately or the openings can be quickly enlarged. Vertical ventilation requires opening an additional path for fire spread.
Coordination. PPA is a coordinated fire attack that is accomplished by the first arriving crew. It offers firefighters the opportunity to make viable rescues and attack the fire more effectively.
Efficiency. PPA allows individual fire companies to accomplish ventilation, fire attack, and search and rescue without waiting for additional resources
Flexibility. If situations arise that crews aren't comfortable with, they can quickly make adjustments or completely stop the PPA operation by doing nothing more than turning off the blower.
Kriss Garcia is a battalion chief for Salt Lake City Fire Department, where he has worked for 20 years. He is an instructor for the National Fire Academy as well as the Utah Fire and Rescue Academy. Garcia sits on the Air Movement Control Association standard review committee and is a Utah-licensed general engineer. He has an associate degree in pre-hospital care as well as bachelor degrees in public administration and education.
Reinhard Kauffmann is a battalion chief for Salt Lake City Fire Department, where he has worked for 28 years. Currently he is assigned as the fire chief for the Salt Lake City International Airport Authority. Kauffmann is an instructor for the Utah Fire and Rescue Academy. He is a graduate of the University of Utah with a bachelor's degree in science.