Positive Pressure Attack and Positive Pressure Ventilation
(PPA and PPV)

There has been a variety of material lately on PPA and PPV, much of which is presented through Fire Chief and Fire Engineering magazines. Click here for links. Let us address here a couple issues that come up regularly regarding positive pressure blowers and how VENTRY Fans solve them.

Carbon Monoxide Levels

In several places, including “PPA: Questions and Answers,” Garcia and Kauffman address carbon monoxide concerns during PPA and PPV and adeptly point out...

“During a structure fire, the CO level is already more than 1,000 ppm in most interior fires. The blower will reduce this level almost immediately and, during most operations, will continue to operate with a CO level near 100 ppm, which, although not good, is much better than 1,000 ppm. When the fire attack is over, taking the time to deploy electric blowers can be done.” (Retrieved November 28, 2007)

We must add, however, that if you use a VENTRY Fan, CO levels will drop to less than 35ppm -- well below OSHA warning levels! With adequate exit for the air, equilibrium levels of all VENTRY Fans are between 17 and 35 ppm. After the initial attack, instead of grabbing the elctric blower, just turn the VENTRY around and use negative pressure to remove any last remaining CO. (Click for more on CO)

Wheels and Shrouds on PPV Fans

In the September article “The Power of Positive Pressure,” we would like to address the section, “What to look for," in which specific features to look for in PPA and PPV blowers are listed. Most of these are valid considerations when choosing a blower, including:

• Blowers should be gasoline-powered for a rapid deployment
• Blowers should be able to tilt up and down to increase their ability to cover an opening if the optimum distance (8-10 feet) between the blower and opening can't be achieved.
• The power plant of the blower should be as simple to operate as possible. The fewer switches the better.

It is not accurate to say, however, that “blowers should have pneumatic tires to facilitate one firefighter being able to maneuver it to the objective.” Our larger fans benefit from pneumatic tires but our most popular 20-inch VENTRY Fan is built light enough for one person to carry without the need for bulky, expensive pneumatics. Solid rubber wheels, standard on several of our larger fans, are also convenient because they are not subject to flats.

With all due respect, the recommendation that blowers should be shrouded is definitely not true. Contrary to this advice, shrouds on blowers do not “...increase the amount of air entrained and therefore the amount of exiting CFMs.” This is easily observed.

The outer quarter of a propeller does three quarters of the work. (Consider how far the tips travel in one rotation versus the center of the prop!) Blocking the air at the tips with a shroud starves the prop tips of air and dramatically increases noise. To see for yourself, hold your hand flat near the outer edge of a running VENTRY Fan’s free-flow guard. As you move your hand closer to the prop, the noise level will increase, because you starve the prop of air. If your hand makes that big a difference, imagine what a 360-degree shroud does!

See more on shrouds, including a true story that illustrates the point!

RESOURCES

All the points we have made here are minor. We are grateful to the authors of this article and their sponsor for the educational advances they have made regarding positive pressure’s benefits. Other valuable PPV and PPA resources:

University of Texas, Austin (UT) and the Austin Fire Department (AFD). "Positive Pressure Ventilation, Training and Research.” <http://fireventstudy.com/> February-15-2008 (Date of access).

Ezekoye, Svensson & Nicks. “Investigating Positive Pressure Ventilation.” (<http://www.me.utexas.edu/~ezekoye/rsch.dir/documents/TravisHouseStudy.pdf>
March-3-2008 (Date of access). Click here for some highlights we pulled from this paper.

Nicks, Watson, and Ezekoye. “Testing Tactics Scientifically: PPV in Residential Structures.” <http://www.me.utexas.edu/~ezekoye/rsch.dir/PPV.html> Presented April 2005 at FDIC 2005. October-6-2005 (Date of access).

City of Phoenix. “Positive Pressure Ventilation.” Last modified 7/10/2002. <http://phoenix.gov/FIRE/20212d.html> October-6-2005 (Date of Access). This is part of the “Phoenix Fire Department Operations Manual, Volume 2,” which is available in total at <http://phoenix.gov/FIRE/start_here.html>

Kerber and Walton. “Effect of Positive Pressure Ventilation on a Room Fire.” (PDF file) March 2005. <http://fire.nist.gov/bfrlpubs/fire05/PDF/f05018.pdf> Sponsored by the US Department of Commerce, US Department of Homeland Security, and the Federal Emergency Management Agency (FEMA). October-6-2005 (Date of Access).

Here are links to some of the valuable educational material on PPV, all of which open in new windows:

• Positive Pressure Attack: Questions and Answers, Garcia and Kauffman, Nov. 28, 2007
• Positive Pressure Attack for Ventilation and Firefighting Webcast via Fire Engineering/Pennwell, by Garcia and Kauffman, originally presented Nov. 7, 2007.
• Pressure Precepts by Garcia and Kauffman, December 1, 2006
• Positive Reinforcement by Garcia and Kauffman, January 1, 2006
• The Power of Positive Pressure by Garcia and Kauffman, September 1, 2005

For more information, please see our webpage on which 19 different PPV Blowers are compared: www.ventry.com/comparison/index.html