Positive Pressure Attack Challenge

Replies to This Discussion

Permalink Reply by Brian Arnold on June 26, 2009 at 11:18pm

Chief,
Thanks for the post. Very informative.


Phil Jose said:

OK It was Austin. Here is a link



http://www.me.utexas.edu/~ezekoye/rsch.dir/FDIC2005Handouts.pdf

Permalink Reply by Kristopher Holien on June 27, 2009 at 1:12pm

Mike,

The point of using the NIST video and wind driven fires was more as an example of the weather conditions that we commonly experience in Seattle. A 5 MPH wind could have an affect on Fire Behavior. Outside of the tactics on a highrise event, Houston recently had a LODD where the wind may have contributed to the fire spread in a residential structure, and ultimately the loss of life ( I am guessing that severe winds is also a contra indicator of using PPA?). It has also occurred in other parts of the US. My attempt was to bring up another case, in which the fire is contained (the box isn't broken) and when the box is broken (either by fire or firemen) then it has a profound effect on the fire behavior inside the structure. While I recognize that a fan can and will overcome such a small force of wind from the outside, during the time in which the window is broken and the fan is turned in the fire behavior can change.



Mike Walker said:

Hey Kris

In an attempt to speak to your questions I think it is important to remember, that PPV in a High-Rise situation is somewhat different then other applications. The window should not be intentionally taken out in a High-rise until wind direction is known but if the window fails and a wind driven fire condition results, then PPV can be used to help alleviate some of the effect.

As to your other question about the 5mph wind. I try to emphasize to my students that PPV is an augmentation to horizontal ventilation. I realize this my stand in the face of strong proponents of PPV but I strongly believe that my statement is accurate. Once the window is gone, either by the fire causing it to fail or by a firefighter, the smoke movement should be observed. If it reacts the way you want it to, then the process can be sped up by using the fan, if the conditions aren't what you're looking for, then more attention needs to be placed on what happens if/when the fan is utilized. The blower can easily overcome up to a moderate wind but to do so the fan placement has to be perfect or damn close to it. The path must be closely monitored in order to maximize the slight pressure increase from PP. The size of the exit opening(s) need to be watched as well. Every window interior firefighters open inside the structure causes a reduction in pressure, thus reducing the blowers effect.

This, to me, is where the rub exists. PPV requires personnel to actively maintain, evaluate, monitor, correct conditions throughout the operation. Most crews are accustomed to performing ventilation and then moving on to other tasks once they have achieved the desired result.

Permalink Reply by Phil Jose on July 2, 2009 at 3:30am

Without trying to hijack my own thread.

Wondering if you guys would be comfortable taking the high-rise stuff directly to compartmentalized multi-family residentials. I'm thinking 3 or 4 story apartments with enclosed stairwells and center hallways. I don't see any real difference in the layout relative to the impact of PPV within such a building as compared to a 10 story. The study shows no negative impact from pressurizing the stairwells. Never. Unless I missed something (which is possible)

Permalink Reply by Mike Walker on July 2, 2009 at 8:29am

Phil,

I've had very good experiences with PPV in the types of buildings you mentioned in your last post. If the crews will place the blower at the base of the stairs and/or entrance to the building and not try to carry it to the affected floor, it does a great job. With that being said, crews have to be cognizent of wind conditions. Now remember, I'm speaking from Oklahoma experience where we routinely experience very high, gusty winds.

Here is another thing we've done that worked well when we've experienced a fire apartment on the windward side of the building. The fire was extinguished but still smoky. We started up the fans and intentionally kept the exit opening small. This allowed an of increase of pressure within the building to the point we were able to overcome the wind. I hope this doesn't mess up anyone's theories but I know it works. But remember, the fire was extinguished before we did this, meaning the smaller exit opening. Also, the option to cross ventilate through the hallway wasn't an option because of the location of the fire.

Permalink Reply by Mike Walker on July 2, 2009 at 8:36am

Oh on a related matter,

We've recently purchased electric blowers. They work fantastic during the salvage and overhaul phase. Good clean air coming into the building. Let me use a fire we made yesterday as an example. Crews had vented the roof due to the attic involvement on a two story (which by the way, they accomplished very fast), they started the gas blowers to augment. The fire was extinguished. After the building cleared of visible smoke, we used a CO monitor to check the levels. They were around 130-140 ppm of CO. We turned off the gasoline blowers, tuned on the eletric blowers, in less then one minute, the CO levels dropped to 10 ppm and reached 0 ppm in less then 5 minutes. True story. We were taking readings upstairs and downstairs.

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