Positive Pressure Attack

Several people have asked me why we don't use positive pressure ventilation for fire attack. My answer is that positive pressure attack works very well when used correctly but has catastrophic consequences when used incorrectly. It takes a great deal of training in live fire evolutions to be able to effectively, intelligently, and safely use PPA. In order for PPA to work you must choose the correct entry point, the correct exhaust point, position the fan properly, perform a thorough size-up to determine that the fire has not entered the attic or any void spaces, ensure that the building is not balloon frame construction, make sure the cone of air seals the entire entry point, and coordinate the timing very carefully. A lot more than meets the eye goes into PPA and you have to get everything right in order for it to work correctly. Conversely, if you get any ONE of these things wrong it can instantly have catastrophic consequences. Watch the video at the link below to see what can happen when PPA goes wrong:

http://www.vententersearch.com/wp-content/jw-flv-player/player.swf?file=http%3A%2F%2Fwww.vententersearch.com%2Fvideos%2Fflv%2Fppvflashover.flv


Now a lot of things were done wrong in this particular incident. As always you cannot see everything from a video but it did not appear that anyone performed a 360. The smoke exiting from the eaves is a sure sign that it is no longer a compartmentalized contents fire but is now a structural fire and has entered the attic space. This is an automatic contraindication for PPA. The fan was entirely too close to the door to seal the entrance with a cone of air. If you don't seal the entire perimeter of the entrance you are not creating positive pressure; you are simply feeding oxygen to the fire. This was blatantly obvious when the fan was started and the smoke began to churn around the door. When using PPA the fan should always be placed and started before the attack crew enters so that you can ensure it is producing the desired effect. The video makes it perfectly clear why this is so important. No backup line was stretched to protect the attack crew. The second line pulled was flowing water from the exterior on the C-D corner. A transitional attack means that you transition from an exterior attack to an interior attack; not conduct the two simultaneously. Notice the lack of situational awareness of the firefighter operating the PPV fan; he was completely oblivious to the changing conditions. This is what happens when you attempt a tactic that you do not completely understand and have not practiced until it has become second nature. You become so focused on trying accomplish that task that you fail to observe what is going on around you. This has happened to us all at some point, though probably not to this extreme. This is why it is so important to practice the basics until you can perform them without thinking.

Again, I think positive pressure attack can be a good tactic in some cases but it is one of the most misunderstood and incorrectly used tactics in the fire service. Before we can add a tactic like that to our skill set we must ensure that we have mastered the fundamentals of fire attack, size-up, incident command, stretching hoselines, communications, and reading smoke.

Amateurs practice until they get it right; professionals practice until they can't get it wrong. Be a student of your profession and master your craft.