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PPV During Defensive Operations
Almost a year ago, we responded to a vacant church fire and found heavy fire venting from the charlie - delta corner. This area of the church was a small office area for the clergy members. The fire started from a malfunctioning heating unit. The church at the time had been scheduled for demolition for six years. Heavy smoke obscured the street on alpha side and the length of bravo side. Command drove through the smoke on arrival and once on the other side of the plume no one could see him. The street was total obstructed by the smoke condition. Within minutes fire was showing from the gable vent on the charlie side.
Command ordered a defensive attack which utilized multple 2 1/2" attack lines. As first due engine officer I called for horizontal ventilation immediately. We only had nine personnel on scene which included the IC and two drivers. I don't know why I called for PPV after the initial natural horizontal ventilation attempt except to say that the interior conditions observed from the exterior still contain heavy smoke and we had written the building off because of the scheduled demolition. If we were going to raise the seat and see how extensive the fire involvement was PPV was the only way to do so without committing an interior crew or venting for life in which we would have destroyed the stained glass. That type of glass as I understand it has historic value. The fire was not showing itself anywhere else except the charlie side. Our attack was concentrated from the charlie side as well.
It appears that the PPV fans on the alpha side helped prevent the spread of fire from the charlie side. I would have expected the large lines to push the fire forward significantly but that did not happen. The church came through relatively unscathed. The interior behind the pulpit wall was gutted but the main structual members were not badly damaged. It was determined that the building could be saved.
I was curious to know if anyone else has had success utilizing PPV in containing fire during defensive attack. I do not have the resources to test this theory. I hope that those of you who do will explore this tactic further. I will be checking the thread periodically and can answer any questions or provide additional information if needed
Command ordered a defensive attack which utilized multple 2 1/2" attack lines. As first due engine officer I called for horizontal ventilation immediately. We only had nine personnel on scene which included the IC and two drivers. I don't know why I called for PPV after the initial natural horizontal ventilation attempt except to say that the interior conditions observed from the exterior still contain heavy smoke and we had written the building off because of the scheduled demolition. If we were going to raise the seat and see how extensive the fire involvement was PPV was the only way to do so without committing an interior crew or venting for life in which we would have destroyed the stained glass. That type of glass as I understand it has historic value. The fire was not showing itself anywhere else except the charlie side. Our attack was concentrated from the charlie side as well.
It appears that the PPV fans on the alpha side helped prevent the spread of fire from the charlie side. I would have expected the large lines to push the fire forward significantly but that did not happen. The church came through relatively unscathed. The interior behind the pulpit wall was gutted but the main structual members were not badly damaged. It was determined that the building could be saved.
I was curious to know if anyone else has had success utilizing PPV in containing fire during defensive attack. I do not have the resources to test this theory. I hope that those of you who do will explore this tactic further. I will be checking the thread periodically and can answer any questions or provide additional information if needed
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Replies to This Discussion
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Permalink Reply by Ben Waller on
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I question the value of PPV for a defensive fire. If the structure is so unsound and/or the fire is so advanced that it's a defensive fire, why risk firefighters close enough to the structure to place an effective PPV fan? You also run the risk of driving the fire to places you can't see. PPV requires an unrestricted path from the fan to the exhaust point. That means firefighters inside, which isn't going to happen in a defensive firefight...as soon as a firefighter enters, it's now offensive.
If it's vacant and the fire is defensive, there's not a lot of point risking the firefighters, the fan, or the risk of pushing the fire in a possibly unexpected direction. See Chris Naum's excellent post on the subject here.
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Permalink Reply by Paul Montpetit on
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Well, an Officer I am not ...BUT, as I tell my patients at work,,,,"I don't care why you get better...only that you get better."...I think the same goes for Fire tactics....Don't care why they work...only that they work...and in this case seems to have worked out well.....Stay safe...keep the faith....Paul
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Permalink Reply by John Crabbe on
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Judging by the photos, I see no problem putting up the PPV or even getting close to building itself, you are on the outside. The building may have been scheduled for demo, so what has been the hold up for 6 years? Was there talk about trying to save the stained glass windows? Point is that if the bldg was vacant and scheduled for demo, why not just let it go? I don't see any exposures issues.
From an attack standpoint and regardless of the reasons the bldg wasn't demo'd, it looks like the PPV helped contain the fire. I attended a class for PPV, and while no where near an expert, some things I took out of the class was that the fan is blowing in COOLER air, reducing the interior temperature as well. Since the windows were still intact, the cooler air kept the fire from extending to the A side, giving the lines a chance to extinguish the fire. PPV also works for exposure control for adjacent exposures, as long as the windows are closed, the PPV increases pressure inside the exposure, making it harder for the fire to spread. (Info was available from the Positive Pressure Attack class conducted by Kriss Garcia and Reinhard Kaufmann).
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PPV in the burning structure also can push the fire, particularly if there is not enough water being put on the fire to extinguish it quickly. That's rarely the case for a defensive fire. PPV also can push very large amounts of heat and flame out the exhaust opening, which can cause autoexposure fires. See the current NIST study which compares side-by-side conventional and PPV fire tests for more on this.
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Permalink Reply by FETC on
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Did your department previously identify this property as a DO NOT ENTER structure? Your description indicated a room and contents fire. We have a few structures in which we are not supposed to enter unless someone identifies there is a squatter inside. I believe from the last update it was a 16 properties.
I have never seen PPV used on a defensive fire but... with the constuction of the church and sheer large volume of space of a church, the reason you are standing inside in your third picture is your PPV pushed the into the rear of the pulpit and out the gable end. Plus there was hardly any fuel in the main portion of the church.
TCSS
FETC
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Permalink Reply by John Kriska on
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PPV can be used for "exposure protection" and it appears in this incident that it was used for that purpose, it kept fire from advancing into the sanctuary and protected those stain glass windows. Fire travels from an area of high pressure (pressure created by the fire) to an area of lower pressure. PPV uses high pressure to direct the fire to an exhaust opening or an area of lower pressure. Understand, that any opening (window, gable etc) that has a direct link to the area of fire involvement becomes an area of lower pressure. This explains why people say that PPV pushes fire throughout a building. How do you resolve this situation? Good tactics and strategy. There is a lot to this subject and education and training are the keys to an effective PPV operation.
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Permalink Reply by Steven C. Hamilton on
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Thanks for everyone's input. To answer many of the questions posted:
The fire started in the rear (C side) and progressively moved towards the alpha side. The fire was not large enough on arrival to justify just letting it go. No visible flames were showing except for a window on the chalie/delta corner. We knocked that down with a few burst from the 2 1/2" line. It was quickly determined that an interior attack was no worth the risk. The first due pupmer was positioned on the bravo-charlie corner and committed for an interior attack. Now that we changed tactics, the concern of pushing the fire from charlie to alpha became very real. I feel that the PPV on the alpha side main door and BIG water from four 2 1/2" lines helped to prevent that from happening.
The building, like many of the WWII era buildings in our district was scheduled for demo. The demo process is very long. The costs are also very high. The cost to demo the building after the fire was about $150,000. The has been some joking and jesting that it would have been cheaper to let it burn.
The point of the post was to see if anyone had any similar experiences. The PPV results was purely accidental. The intent was to clear the smoke out of the sanctuary area and assess the fires progression. The area in question was so big that there was no other way to ventilate with out causing major damage to the windows. Since the building was set to be destroyed what did it matter?
The other significant fact was that the IC made a difficult decision to keep people out of the structure. Many of the new and eager firefighters were quite unhappy about not being able to enter straight away and get low. In this case there was no reward for risk. Had this been an occupied church or one that was used readily the tactics might have been different. People say that you should risk a little to save a little and risk a lot to save a lot. I TOTALLY disagree. You should risk nothing to save a little and risk a little to save a lot. The attitude of go and get it hard needs to change so that we stop killing each other.
I thought that this might be a PPV tactic to expoler in big box structures or ones that are known to have large open areas when the fire attack occurs from the opposite side of the unburned area.
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