By Kriss Garcia
Despite that fact that departments that have trained in using fans and successfully use them during fire attack loudly exclaim the benefits of a coordinated attack, they are mocked and belittled by departments that do not use fans in this manner. I call the latter firefighters “traditionalists.” They consistently convey the message that any pressurized fire attack is less than heroic and that the departments using them are mistaken about their first-hand observations. The majority of the fire service considers advocates of the pressurized fire attack outsiders, or even traitors. This antifan traditionalist movement will win, and the coordinated attack will never be mainstream or widely accepted, since the historic system of traditionalists is stronger than any proven tactic that does not fit the stereotypical mold of a firefighter. Statements made by some traditionalists to the effect that we get paid because we take risks and a pressurized fire attack takes all the excitement and fun out of firefighting are often heard and reflect misguided logic.
Traditional Fan Use
Most departments use fans for post-knockdown applications when the initial crews are in high heat and awash in the carcinogenic and gaseous unpredictable hot fuel we most often refer to as smoke while, at the same time, working in an environment where their vision is greatly obscured. The most common request from interior crews during an uncoordinated attack after disruption of the thermal balance is for ventilation; fans are set up after knockdown.
Pressurized fire attack occurs prior to and in coordination with fire control. During this attack, crews are in low heat with limited smoke, thereby working in a nontoxic environment where they are not impeded by heat and smoke. This attack is used to allow the solid fuel already on fire to burn cleaner, producing less smoke as crews make adequate exhausts most often through windows in areas of the building that were already unsurvivable. During a coordinated attack, hot fuel is removed from the dwelling as crews make their way to a clean-burning fire. The common report from these crews is that they are in low heat with good visibility.
The Fire Triangle
During a post-knockdown fire attack, heat and extensive amounts of gaseous fuel in the form of smoke are still present within the structure with our firefighters and the victims. Oxygen is not present. Post-knockdown ventilation not only causes disruption of the thermal balance, but it also increases turbulence and dilution of a potentially lethal environment that may have previously been too rich to ignite without the missing ingredient, oxygen. Post- knockdown ventilation will contribute to aggressive fire growth if ignition of these fire gases occurs in the confines of a structure with inadequate exhausts. The major problem is that when the third side of the triangle is introduced, firefighters and victims are in the structure still hampered by poor visibility.
During a coordinated attack, on the other hand, hot gaseous fuel or smoke is no longer pervasive within the structure. Oxygen in the form of cooler fresh air is introduced. Without the other two sides of the triangle present, unintended ignition and rapid fire growth of the smoke and gases do not occur other than at the already unsurvivable exhaust areas. In effect, this coordinated attack is allowing the predictable solid fuel already on fire to burn clean, producing little smoke. Ignition of the smoke, IF it occurs, does so as products of combustion exhaust from the structure through areas already unsurvivable while crews are making their way to the fire without being impeded by smoke or temperature. Another benefit of this coordinated attack is that cooler, oxygen-laden outside air remains at the floor level, giving victims not already dead from the initial assault of the fire a better chance of survival because firefighters can more quickly find them and they are not compromised by the environment the post-knockdown attack causes throughout the lower areas of the building.
Where We Go Wrong
Over the past 30 years, structure fires and our tools have changed dramatically. Some of today’s basic firefighting curriculum supports questionable tactics when associated with pressurized firefighting tools and tactics. The limiting figures generally accepted today to determine the appropriate exhaust size are contraindicated by every empirical study regarding pressurized fire attack as confirmed by the National Institute of Standards and Technology (NIST). Emergency Engineered Solutions (EES) has also conducted hundreds of live fire evaluations and also confirms that limiting the exhaust to anything less than twice the size of the ventilation point can have grave consequences.
Fire
Fires of today are producing ever-increasing levels of lethal smoke attributed primarily to the synthetic nature of our modern-day fire loads. These products of combustion are more fuel than air. In fact, in John Taylor’s book Smoke Burns, he refers to modern-day smoke as being very similar to “petrol vapors.” In fact, this environment is so laden with particles and colloids that it has the characteristics of fluid. In all actuality, those who study fire and its behavior use the science of fluid dynamics to evaluate and predict fire behavior. The National Fire Protection Association (NFPA) has determined that fires that occurred 30 years ago progressed from their incipient stage to flashover in 14 minutes. Today’s fires grow to the stage of flashover in less than four minutes. The fire environment has changed dramatically, and for the worse.
Fans
Fans have also changed dramatically in the past 30 years. When the first mention of pressurized tactics started in the late ’70s, fans were moving fewer than 5,000 cubic feet per minute (cfm). These fans were the box type, axial electric smoke ejectors. Today, gasoline-powered portable fans are creating 20,000 – 30,000 cfm. Fans have changed dramatically for the better.
Convection
Even with these very dramatic changes, the same one-quarter to one and a half times the exhaust in relation to the ventilation point has remained unchanged in many publications for more than 30 years; this could not be more incorrect. Limiting the size of the exhaust to anything less than two to three times or two to three windows in effect creates a convection oven within the structure. Given the fire loads of today, this is a lethal circumstance.
Convection ovens cook up to 50 percent faster than a conventional radiation oven. If it is our intent to make the interior environment hotter and keep more of the fuel or smoke in the structure while forcing it to lower levels for a longer period of time, then we should follow this commonly held limited-exhaust practice. Limiting exhaust ensures that the heat and fuel sides of the fire triangle are present in the structure while firefighters and victims are inside. Under these conditions, adding the missing ingredient of oxygen either through the use of fans and limited exhaust or the mere failing of a window will result in more firefighter injuries and property damage. If you want to remove the heat and unpredictable fuel in the form of smoke, you should amply exhaust before advancing crews through windows in areas of the building already unsurvivable.
Another justification sometimes used to justify limited exhausts is to enable crews to more easily remove the smoke from the building after an under-control, during salvage. Common sense is challenged when we intentionally make the portion of the fire attack that could immediately kill you and victims more volatile and hazardous for a longer time so we can remove the nuisance smoke from the building after the fire is out.
Fire Behavior
Fire is neither scary nor unpredictable. Fire is simply the ignition of gases as fuel decomposes. Fire is at its peak of energy release. Smoke is scary and unpredictable Smoke is screaming with potential energy that may become fire and does so in a violent and deadly manner when confined to a structure.
A statement made by many who are not familiar with fire behavior during a pressurized fire attack say that fire crews need to know the fire’s location before they turn on the fans. For years, I simply agreed with this statement, as is done in the case of many fireground myths or catch phrases. This was the case until I participated in and witnessed hundreds of live fire tests as well as actual structure fires over the past two decades. Regarding the safety of the attack crews and victims, you don’t need to know where the fire is in the structure; you just need to know where it wants to exhaust. If this is not obvious, I would not use a pressurized fire attack.
Fuel has started burning where the fire originated; physics has already moved it to an area of lower temperature. More often than not, this is toward the exterior on the leeward side of the structure. Why not allow fire to continue to go where it wants to go while crews anchor the fire and operate on the backside of it in a coordinated attack?
During this coordinated attack, we are removing two sides of the fire triangle while at the same time making the environment where any victim who has not already succumbed because of proximity to the fire more tenable. Experiments conducted by EES and confirmed by NIST, show that in a structure fire, the survivable environment (24 inches from the floor) increases in tenability almost instantaneously as soon as fans are started with ample exhausts. It is not uncommon to take carbon monoxide levels from several hundred parts per million (ppm) to less than 100 ppm—and with cooler oxygen-laden air.
Pressure
Physical laws including Charles, Boyles, and the Combined Gas Laws, as well as the Bernoulli Principle, define why a pressurized fire attack has to work. These laws which all govern the behavior of our universe are physical laws of science that are as irrefutable as the law of gravity. The massive difference of pressure between the fire area when compared to the much lower pressure on the exterior, makes the practice of a pressurized fire attack irrefutably one of the safest and most predictable fire tactics when performed correctly by having crews anchor the fire with a fan, exhausting the lethal environment ahead of them through areas already unsurvivable while increasing the tenability of areas in the structure where victims are.
It’s All about Survival
For a moment, consider the evolution of our personal protective equipment (PPE). As evidence that our environment has become much more aggressive and lethal, PPE has become more formidable over the past 30 years. We need this increase in protection to survive fires of today. Consider our victims’ viewpoint; they have no PPE. If we were wearing what they were wearing, we wouldn’t do to them what we do to them. When a fire starts to grow, it seeks and, in effect, brings to it, the coolest and most oxygen-rich environment remaining in the structure. The fire is supporting what we teach children during the Exit Drill in the Home (EDITH) educational program: Stay low; that is where the freshest and coolest air is located. If we use a post-knockdown fire attack, we stop this process and redistribute the lethal environment of carbon monoxide and hydrogen cyanide–not to mention dozens of other products of combustion, several of which were used as World War I chemical warfare agents–down to the floor level along with unsurvivable levels of heat–this while we cause increased obscuration that makes our task of finding these victims much more difficult.
Fire Spread
When fans are used incorrectly, which most of the time occurs because the size of the exhaust is limited, flame may indeed spread throughout the structure. If you want to burn a house down and place firefighters and victims in lethal temperatures, create a convection oven by using fans with limited exhaust after firefighters have already entered the structure brimming with two sides of the triangle. If you want to give victims who have not already succumbed to fire because of their proximity to it a better chance of survival and remove the majority of the interior temperature and fuel while allowing your firefighters to operate in an environment where they can see, consider a coordinated pressurized fire attack.
BIO
KRISS GARCIA, 30-plus-year veteran of the fire service, is the chief of the American Fork (UT) Fire Department. He retired from the Salt Lake City (UT) Fire Department after 27 years. He has had articles published in fire service periodicals and is the author of a book on fire tactics.
