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PPA
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Permalink Reply by MalteseMonster on
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https://youtu.be/iTInZhv4ZyE
Positive pressure flashover. You can tell by the smoke that it was looking for air, flashover conditions showing!! Then add a big ol fan to the mix. As the ul studies have shown, the front door not only let's heat out but also brings air in. This bidirectional flow is what makes firefighter induced flashover a ever present danger! We let more air in through a door opening than we let heat out. Fans complicate that further since a larger exhaust port would be needed to change the fires flowpath, otherwise it just disturbes it and adds air! Both not good for inside crews.
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Permalink Reply by captnjak on
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The following is my interpretation of the report, which I previously posted elsewhere:
1) We were always told that the entry point should be monitored and if smoke started to show at the entry PPA should be discontinued because the exhaust opening was not large enough. The research revealed that the entry opening is bi-directonal. (Apparently ALL openings cause bi-directional flow.) As is the exhaust opening. But BOTH MUST BE MONITORED CONTINUOUSY. That's two firefighters married to observation posts. I can find better things for two firefightes to be doing.
2) There was always a lot of talk about the cone of air made by the fan. And the exact distance of the fan from the entry door. Turns out it barely matters.
3) There was a lot of talk about the sixe of the entry and the size of the exhaust. The size of the entry opening where the fan is located does not matter. It is only the size of the entry door to the fire compartment that matters.
4) The size of the exhaust opening is critical. It MUST be larger than the opening to the fire compartment. A bedroom with two standard sized double hung windows is not a candidate for PPA. Because the volume of window opening is about equal to the door opening. The research did not quantify exactly what the ratio should be. I believe it indicated that 2:1 was adequate and 1:1 was not. But I believe the average American bedroom may be off the list of areas where PPA is indicated.
5) PPA is not indicated in open areas or any area with high ceilings. I don't believe they quantified how large of an area is too large. Or what height ceiling is too high. But compartmentation is a key factor. I believe many kitchen/dining room/ living room/ family room fires will not be candidates due to the fact that they are often open to each other to some degree. Even older homes are often renovated in this fashion. An outside survey will not reveal this fact.
6) I think points 4 and 5 put a major dent in the PPA tactic for many homes in America.
7) The research indicated that any disruption to the flow from the fan could allow fire to blow back (my term not theirs) in to the structure. A team of firefighters advancing a line down a hallway or advancing to search could disrupt the flow of air toward the fire compartment (remember it's bi-directional). Fire will then come at them. The idea that we can set up a fan and judge how well it is working prior to committing firefighters is not valid. Because committing firefighters can change the fan's effectiveness.
This was the most surprising thing I learned.
8) The researchers acknowledge that ventilation is always a wild card. They say PPA is more of a wild card than normal horizontal and/or vertical ventilation and that it can have more negative impact than those conventional methods do. I've always argued against PPA based largely in part on what I called "volatility" of the fire area once air is introduced.
9) The researchers found that the most important aspect of PPA is rapid application of a sufficient water stream. Guess what? It's also the most important aspect when NOT using PPA. They also stress the importance of using the reach of the stream to maximize effectiveness. So why bother at all? PPA wastes time and manpower, which are all too valuable on the fire ground. It doesn't, according to the researchers, allow us to get closer to the seat of the fire before opening line.
A well executed conventional attack will accomplish all the same things. Pair that with transitional attack where appropriate. The additional manpower will make the stretch quicker or the search quicker. And no time wasted setting up and evaluating the fan and it's effect on the fire.
I admit my great fear concerning PPA was disproven. My fear was that it could routinely worsen fire conditions, possibly to a very dangerous level for firefighters. The researchers acknowledge the possibility of this happening. It appears that I may have over-estimated this threat. But I believe it still exists and I suspect that departments who use the tactic will not be dissuaded. I hope they are ready with quick water but I doubt it because they generally seem to endorse the wait and see what happens approach to fan operation.
The conclusion for me is that since rapid water is key to success there is no other real benefit to PPA. It is IMO an unnecessary complication to the equation. It doesn't save manpower and it doesn't on it's own make firefighting safer. And it wastes time (assuming the evaluation period is honored). Civilian occupants don't have time. And if it doesn't prove successful the fire has had time to grow, making final extinguishment more difficult and less safe.
I believe the conclusion for those who use the tactic will be that there is no reason to stop using the tactic. I hope they'll at least incorporate the lessons learned in to their use of it.
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I remember when we first got our big ol fan, cleaned out a entire box on the truck, and felt better equipped to do the job. Some concepts of ppa were being trained locally at the time (leading to its use today) but it never gained traction with most departments. Only took a few bad experiences on the fire ground for us to quit using ppv with our attack. Absolute door control is a must! Which in a way correlates with some of the ul studies. The way I understood the teachings of ppv, the proper cone at the door was to create a inlet and destroy the bi directional flow (we just called it turbelent super heated gas) that was coming out of the door we just opened. It worked if all the rooms not on fire had the door closed, the room on fire being hit by the attack team, and the back door open. That meant to us that not only did you need two men watching front and back entry, but another door guy inside. If we had that many to spare I too could think up better tasks!
Its my opinion that ppa has too many variables to be considered viable in real world conditions. It was also considered a key element in the deaths of two brothers in Texas back in 2007. Doors being different sizes, or different elevations, each make or break the effectiveness. I kinda wished it didn't work at all! It would be easier to get folks to stop reaching for it that way. Sucks that the people who have the biggest problem with it seem to be the ones that get most their experience from burn buildings. Least its that way here anyway :(.. They should market ppv for burn buildings though! "When you absolutely got to burn the building over and over, nothing makes re loading quicker than this big ol fan"!!!
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