Positive Pressure Attack – The Rules of Engagement
Early in our careers we are taught that our fire attack should be done in coordination with ventilation. We were convinced, and rightly so, that ventilation provides a safer environment for us and for potential victims. Decades pass and what appear to be small changes occur. Fire loads, construction, energy efficiency attics, solar power, fire department resources, Personal Protective Equipment, (PPE), fire equipment and the fire service culture are some of these changes. None of these events come in with a bang, they are slow and on a daily or yearly basis may be unrecognizable.
If you took a snap shot of the fire service 30, 50 or 100 years ago and put it next to the environment of which we operate in today; the change is astronomical. We know that change in the fire service comes slow, yet change we must.
For over 30 years many fire professionals have been safely using fans to ventilate buildings in coordination with the attack. I know without any shadow of doubt that when used correctly at fires and buildings, which are conducive, that there is no safer fire attack for civilians and firefighters.
With Positive Pressure Attack (PPA) not only are firefighters not in obscured, flammable, carcinogenic environments but victims who may be in areas that are survivable on our arrival are also benefited. In order to consistently use this safe and predictable fire attack, we have to wade through years of myths and under-educated false starts and provide a foolproof way of implementing this tactic when it makes sense to do so. We will call this effort; The Rules of Engagement.
First some ground rules. Positive Pressure Attack (PPA) is a coordinated fire attack where fans are used to assist in controlling the fire. Positive Pressure Ventilation (PPV) is the use of fans to remove the products of combustion after fire control.
For interior crews, successful and safe fire attack is much less about fighting fire than it is about fighting smoke. We spend an inordinate amount of time protecting others and ourselves from fire when we know what hampers our ability to operate inside of a structure fire and what kills civilians is most often times not the fire but the smoke. More accurately, civilians succumb to the high levels of carbon monoxide and other toxic chemicals as they try to escape the very unfamiliar highly obscured Immediately Dangerous to Life and Health, (IDLH) conditions. As for us, without ventilation we are operating blind in a highly volatile often times unpredictable, toxic atmosphere of potential energy mixed with substantial carcinogens.
Most reports demonstrate that vertical ventilation, while effective, is highly dependent upon a tactic that requires extensive resources and takes several minutes longer to accomplish than it does to extend fire control lines. Therefore firefighters and civilians are not reaping all the benefits of operating in a properly controlled ventilated fire. Instead they are in a non-ventilated, volatile atmosphere that when water is applied causes increased temperature, increased carbon monoxide and decreased oxygen at the victim level in the structure.
Gas cooling while effective, requires specific nozzles and pressures that often times are not common place and also places firefighters and victims in a precarious atmosphere where conditions for those not protected to the same level as us, may decrease the survivability. Imagine what we could accomplish if we could remove the gases and associated obscuration as we entered?
The Rules of Engagement:
The structure has to have windows or doors that can be quickly opened from the exterior in order to use PPA. Unlike vertical ventilation, with PPA the fire can occur on any level of the structure and still have positive results as long as there are windows present. Adequate exhausting is relative and will be talked about later as to when you know it is adequate. Basically large fire=large exhaust. Small fire=smaller exhaust. PPA’s main objective is about being able to remove the un-survivable environment away from the high pressure or clean side of the fire our crews are in, towards the lower atmospheric pressure which we have already determined to be non-survivability or the dirty side of the fire. As a rule of thumb, windows where the immediate area behind are non-survivable can be removed, or most often times have already failed. Several studies summarize window failure to begin when there is a difference in temperatures of greater than 370 C on either side of the glass.
Fires should be in the free burn stage. Free burning fires require approximately 21% oxygen. The fan simply provides the same percentage of oxygen that already exists. Studies show that the temperatures after the fan is introduced and the fire is cleaned up, will increase slightly above the original levels that you have already determined are well beyond the threshold of survival.
- Ensure structure has windows/exhausts on the fire floor and that there is a free burning fire.
- Identify windows or doors where there is a high probability of no one being alive in that area of the structure.
- If substantial winds are present, do not take exhausts on the windward side of the structure.
- Position and start a fan at the attack entrance. Do not direct the airstream into the structure until exhaust is ensured.
- Ensure attack lines are ready to make entry.
- Ensure ample exhaust is made.
- Turn fan into building.
- Before entering, observe the area above the cone of air, we will call this the barometer, and ensure it is clearing. If this area does not begin to clear within 15 – 30 seconds, there is not enough exhaust on the dirty side of the fire to use PPA.
- If exhaust is adequate and lines are in place the fan can be turned into the building and entry can be made.
- Enter the structure a short distance and position the crew so that they are not interfering with flow of air.
- As interior conditions begin to become less obscure, cooler and more survivable on the clean side of the fire, crews can then advance to and extinguish the fire.
- When applying water or moving down small corridors, stay low to maintain the benefits of the high-pressure area you created on the clean side of the fire.
- If you are ever interior with a fan operating and conditions do not obviously clear, remove the crew from the structure and re-evaluate.
Amplification of PPA:
- Fire has and always will increase the pressure in the area of ignition due to increased temperature.
- Fire has and always will burn from an area of higher pressure to an area of lower pressure.
- Fire has and always will move to an area/opening with the least amount of resistance.
- Fire burning yellow, red and orange has and always will burn at approximately 1000 C.
- Fire has and always will use the 21% oxygen available in the atmosphere when it is free burning.
- Fire has and always will continue to move in the same direction given the affecting conditions remain static.
- Fire has and always will kill any civilian who is in the room or area that is hotter than 100 C and full of lethal levels of carbon monoxide.
- Fighting fires in buildings where we can see has and always will be safer for firefighters and victims.
Recent studies demonstrate that fires which, were well above the lethal threshold in regards to temperatures, degraded to a few hundred degrees Celsius when no fresh air was available. Once a fan was introduced and exhausts opened, temperatures again arose to and slightly beyond, the earlier non-survival thresholds.
Just because you take a fire area with thousands of parts per million of carbon monoxide and temperatures in excess of 1000 C and drop it to 200 C, that does not equate to resuscitation. Conditions near the fire have not been survivable by any civilian just a few minutes after the fire has started. A well-seasoned firefighter explained this fallacy in an analogy. He stated, “It’s like drowning in 10 or 20 feet of water, regardless your still dead”.
The goal in PPA is to allow the fire and associated high-pressure to move away from attacking crews through areas that are already non-survivable towards the lower atmospheric pressure through exhausts the fire or our crews have created. The PPA does not have to beat the pressure that the fire is creating; it only has to be higher than the atmospheric pressure outside the structure.
I have never had or heard of a firefighter falling through a flowerbed while performing PPA. With PPA, firefighters are also not subject to a completely obscured, flammable environment with high levels of carcinogens and toxins. We can see where we are going and never go beyond an area that the fan can clear. We know that if we use PPA and the interior environment is not clear, that something in the procedure is not as it should be. When these conditions are present do not advance deeper into the structure; instead reevaluate your circumstances from the exterior until such time that you can determine what portion of the attack is not as it should be.
Not only is this attack much safer for firefighters today, it is much safer for them tomorrow. We all know of too many tragic circumstances where friends who have worked in the business for years have contracted career and life ending cancers. Removing the carcinogen-laden atmosphere from the interior as firefighters approach makes tomorrow much safer for all of us.
The above conditions have been proven time and time again over 30 plus years to provide firefighters with a safe and predictable fire attack. Yes, there are a few assorted “what if’s” that cannot all be explained in this brief article, but Despite these infrequent circumstances, keeping to this procedure will provide your department with another option when it comes to attacking fires of today.
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