Positive Pressure Ventilation

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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

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6 thoughts on “ Positive Pressure Ventilation

  1. 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 structur