Positive
Positive Pressure Ventilation
The Title is that; Ventilation. To effectively attack a fire requires multiple tactics performed by trained firefighters. Extinguishment requires water on the burning solid fuels. To support this so crucial fire ground function, we let the products of combustion out by horizontally or vertically, making use of an existing opening or creating one. Coupled with proper timing, the heated fire gases will rapidly release to the outside. Forcing theses gases out by means of a high pressure can, and will intensify the fire’s growth. If the opening is too small, a back pressure will be created. The fire will be forced back on the advancing attack team. This back pressure can also force fire into other areas of the fire building. If we can get the attack team in rapidly to apply water on the fire; we can then provide positive pressure ventilation to remove residual smoke without the concern of feeding/pushing the fire into unwanted areas of the fire building. The individual assigned to place the fan at whatever entry point should and could be used to assist getting the attack line in place quicker; to possibly eliminate the flashover event. Question when the fan is in place before water has been applied to the burning solid fuels. Why would you provide a working fire with high pressure oxygen?
Once the fire has been knocked down, you can then consider positive pressure ventilation to remove the residual smoke. The fan should only be placed into service when it has been confirmed the attack line is still manned for any possible flare ups or hidden fire that will show itself. The fan should also be manned with a firefighter monitoring the attack channel for orders to shut off the fan.
Remember that hot dry smoke naturally wants to take the path of least resistance to the open atmosphere. There really is not a need to force it out before water has been applied. If ventilation is required to make the push; utilize decades of proven ventilation tactics. When opening the door for entry of the attack team; consider if this will be the path of least resistance for the fire and the products of combustion that have been created. If so, vent in close proximity to where you believe the majority of fire has occupied the structure before entry. Once the door and/or vent opening has been created you only have a short time to eliminate the enemy. There are no time outs.
AVS Attack, Vent, Search.
VAS Vent, Attack, Search
Study Top Photo and then Bottom. Compare the two and what changes have transpired.
Photos by: Phil Cohen, Camden NJ
Can you read between the lines?
Hey Phil!
Thanks for the chance to weigh in on this subject, I hope not to embarrass you … or myself!
While I do not think myself as an expert in the field, I have been trained using tactics/information/techniques from some of the best in the field (McGrail, Pressler, the seattle guys, and the KC guys). I think knowledge is power, and working use (applied) of that knowledge makes a fireman squared away. That being said … the most striking differences between the two photos is the obvious (to me, anyway), the top photo is pre-vent, the bottom is poet-vent … I think he results are more than obvious to the trained eye. Creating more openings allows more pressure to escape, along with the escaping pressure goes smoke, heat, and lack of visibility. I am going under the assumption that everyone understands having an attack line in place and ready to rock is imperative before venting (unless for life) or turning the fan on to create positive pressure … but then again, this is the fire service never assume.
DISCLAIMER: wind direction is always vital when it comes to ventilation or firefighting tactics.
Ventilation, natural ventilation is the release of pressure naturally from a high pressure area to a lower pressure area. Simplified, but my hope is to create an understanding of the differences between the two.
Ventilation, PPV is introducing greater pressure into a designated area of high pressure, and overcoming it to artificially create a predetermined flow path for the release of pressure/smoke/gas/heat out into the lower pressure area (atmosphere).
The differences are great, and the results can be extremely effective if you understand the simple concepts of why when, and how to ventilate, combined with building construction and fire behavior.
Fire creates it’s own pressure that some describe as wind, but this pressure is recognized and measured in what is called pascals. So, the pascals created by a class A fire (training per 1403) can reach some where in the low 20’s, and the maximum heat attained (under perfect conditions) is roughly 1800 – 1850 degrees. You must be able to create at least 1/2 more pascal with your fan(s) than that of the fire (the class A pascal example is merely your jumping off point) The significance for this is your reference point when buying fans for ventilation, combined with average square footage structures in your area, and the low frequency high risk structures, not to mention modern homes release heat much quicker due to polymers in furniture … but I digress … for pressurizing stairwells (high-rises) this information is as important as clearing a house, or using PPA. You have to have a solid understanding of pressure and how it reacts to be able to efficiently overcome it.
Over pressurization will cause pulsing through the intake, which means inside the boys are talking a beating, getting scalded, and possibly die. The turbulence created this way is similar to opening a fog nozzle on a fie with a wide angle while your inside the structure … it sucks, and it shows your ignorance.
While there is no “legitimate documented” (NIST, or UL) numbers on discharge openings, it is my experience, and apparently the opinion of many ventilation guru’s across the country that the opening vary’s in size depending on your goal. To create PPV the discharge opening size is more forgiving than the needed opening for PPA. To understand this thoroughly a ventilation class with lecture and H.O.T. is necessary to get complete buy in … thats the best I can do with the written word, hope it helps add some clarity … stay low, and stay strong brothers … we rise and fall together.
RFB
thats pre-ventilation, and post ventilation … not poet … autocorrect
I’m open to all options reference tactics. I do however believe PPA requires discipline and serious understanding of the things. Ric Jorge commented on. Miss applying PPA can cost you big time. When in doubt stick to old school tactics. I have seen to many times where PPA has been catastrophic. Water on the Fire!!
I Think Ric said it better than I could ever hope to. You need to have a solid understanding of what your doing in regards to applying a particular vent tactic. Also a great summary of the different types. Each tactic has its place depending on the situation at hand. There’s times when all you need is to take a window or two, times when you need to to let it out of the top, and times when you may need to blow it out the window. I do think, however, that sometimes positive pressure attack gets too much of a bad rap. There are likely as many instances where windows were taken haphazardly, or someone cut an improperly placed/undersized hole in the roof. Like both natural and vertical, the goal behind PPA is that you can control the flow path, enabling an easier push to the fire, as well as clearing the IDLH away from potential victims. Ideally, the backpressure on an advancing nozzle team should not be an issue, as the team doesn’t make entry until after a brief pause for assessment of the space above the air cone to judge effectiveness/ineffectiveness. This pause is said to be offset by a now faster push to the fire room. The key elements to all of the different vent tactics are, as Chief Isakson mentioned, understanding why you’re employing that tactic, along with having the discipline to perform it properly. I would love to be making the roof on every fire, but I know that it’s not a likely reality in my organization (although my crew still trains to be proficient in it). Our vent focus (my dept.’s) needs be on getting crews to take windows properly, and to stop using the fan in a way that should have gotten one of us hurt by now.
Nate, I think you and Curt hit on something very important … one of those things that are taken for granted in FD’s … it’s called education and experience. My FD is suffering from it right now. We have a lot of managers in place at HPGP (High Pay Grade Positions) where there should be leaders.
Leaders … motivate, and inspire … they lead by example, they train because they know the significance of being properly informed is the step prior to being properly armed. Leaders know it is imperative for their people to understand the big picture in order to get complete buy in, creating a thriving environment for successful, functional training.
Managers … thats what franchises have.
I’m trapped in a franchise … would you like fries with your order?