Positive Pressure Ventilation (PPV)

FDIC 2005 Presentation Handouts for "Testing Tactics Scientifically: PPV in Residential Structures"

Positive Pressure ventilation is a tactic used by the fire service to clear smoke and heat from the fire-attack corridor.  A fan is placed at a vent (usually door) of a structure and is used to drive smoke and heat out of the structure through an exit vent (either door or window).

PPV has been shown to increase fire fighter visibility and reduce the risks of extreme fire behavior in the attack corridor.

Questions remain on the impact of PPV on flame spread, toxic gas and heat dispersion downstream of the fire. 

Our work has focused on experiments and computational fluid dynamics simulations that can clarify when and how to use PPV.

Tests  that were conducted in December 2002 required significant resources and coordination between the Austin Fire Department (AFD) and our UT research group.

Relationships

UT-AFD: Prior to the burns of December 2002, there had been ongoing collaboration between UT and AFD on PPV.  Chief Bob Nicks and Prof. Ezekoye had been working together on the subject.

AFD-City of Austin:  The City of Austin had created a Public Safety Training Lane at the Hornsby Bend Biosolids facility.  The city had acquired homes on the site in eastern Travis county for training public safety personnel.  The homes are managed by the wastewater facility, and a memorandum of understanding allows UT-Austin access to the homes for testing.

ME 382 R Fire Dynamics: For the December 2002 burns, Ezekoye was teaching Fire Dynamics, and the timing of the burns presented an opportunity for the class to participate in the design and implementation of the tests.  This was a unique learning opportunity, and also an opportunity to gain insight into public service issues.

House Geometry

A fire room and a downstream "victim room" were designated.

The house was fire-hardened so that multiple burns could take place within the house.
 

Quick open vents and observation ports were placed throughout the house.

40 Channels of thermocouple data were distributed on thermocouple trees between the fire room, hallway, and "victim room".  Note that the thermocouple trees (steel columns) in the "victim room" each have 8 thermocouple leads.  A CO extraction port is located near the mannequin's head.

A data acquisition shed sits approximately 40 feet from the house.  Thermocouple data as well as video data from 4 cameras including an IR camera are fed into the data shed.  Wind speed and direction data is taken prior to any test.

A specially constructed burner was constructed  to minimize variation in fire heat release rates associated with ignition.  Live-fire-test rules were followed and thus only approved fuel sources were used.  Uniform polyurethane foam pads were used as the fuel. A propane ignition system was used to ignite the samples. A sliding fire barrier protected the foam samples from the burner until a prescribed time at which point the barrier was slid away exposing the foam fuel to the burner flames.

Approximately 700 kW/(sq. meter) was produced by the 12 pads.  The heat release rate was approximately 2 MW.

Coordination and Timelines

Assuring safe operation was the most critical factor in these tests.  The fire department Incident Command protocol was used.  The AFD organization required each of the following:

Attack Group Back Up Group Ventilation Group Rapid Intervention Group Dedicated Safety Officer Ignition Team Incident Commander (Chief Robert Nicks)

The general timeline followed was:

Time = 0: ignite foam
Time = 1:45 min : Vent window
Time = 2:00 min: Start PPV
Time = 2:45 min : Start Attack (Confirm fire knocked down and fire out)
 

Matrix of Conditions

For a few cases we also considered venting both rooms.

Results

The picture below shows a typical view of the fire room after it was vented.

Raw temperature data taken on the first day of testing is shown below:

CFD simulations using NIST Fire Dynamics Simulator helped us understand how the flow patterns associated with venting could affect the temperature distribution in the downwind compartment.

Reduced data show that for the downwind compartment there is more cooling at the elevated measurement points with PPV than without PPV.  It also shows that there is a slight increase in temperature at the lower elevations that is likely to be associated with a mixing flow which takes hotter fluid from the top of the room and mixes it into the lower layers.  These effects are accentuated by venting the downwind compartment.  Venting the fire compartment has less of a mixing effect on the downwind room.

We have continued to computationally and  theoretically analyze the data acquired during the 2002 burns.  Continue to check for updates as we proceed forward.

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