Positive Pressure Ventilation (PPV) in high-rise fires

This is a simple example of how scientific simulations can help us understand the fire dynamics and verify the efficacy of new firefighting procedures. The analyses of following FDS (Fire Dynamics Simulator) simulations demonstrate the effectiveness of PPV operation in mitigating the smoke and heat that may help to create tenable conditions for firefighters. The effectiveness of PPV was analyzed by comparing the spread of heat and smoke in a typical high-rise fire, with and without deployment of PPV fans.

Simulation A: Fire without deployment of PPV
Simulation B: Fire in the presence of deployment of PPV

Both simulations have the same timeline, fuel load, and input conditions for fire in an apartment on the fifth floor. The fire apartment is furnished with a sofa, carpet, table etc. representing a typical fuel load in a residential structure. The fire is assumed to start under the sofa in living room. The apartment door is assumed to be left open by the occupants. The fifth floor stairwell door and bulkhead door (top roof door) is initially closed.

As the fire becomes fully developed, the smoke and heat rapidly spreads inside the apartment and in the T-shaped public hallway. After a certain time, the fire apartment window is assumed to fail. When the fire is fully developed, a firefighter opens the fifth floor stairwell door. The only difference between these simulations is that in simulation A, the firefighter opens the fifth floor stairwell door without the deployment of PPV fan, and in simulation B, the firefighter activates one PPV fan at first floor stairwell door to pressurize the stairwell and then opens fire floor stairwell door.

Notice the temperatures across the plane perpendicular to the stairwell door, the spread of smoke, and visibility inside the stairwell in both simulations.

Observations:

• ✓ Without the deployment of PPV fans, in simulation A, as soon as the firefighter opens the fire stairwell door, the smoke and heat rapidly propagates from the fire apartment and the public hallway (high pressure zone) into the stairwell (low pressure zone), which can create untenable conditions for firefighters and civilians. The visibility inside the stairwell is also decreased; this may create more problems in rescue operations.
• ✓ With the deployment of PPV fans, in simulation B, when the firefighter opens the fire stairwell door, the spread of smoke and heat into the stairwell is mitigated due to the positive pressure created inside the stairwell by the PPV fan. In comparison to simulation A, the temperatures inside the stairwell are reduced and visibility inside the stairwell is increased helping to create tenable conditions for firefighters.

As discussed in subsequent sections, the performance of PPV operation can be improved by deploying multiple PPV fans at proper positions and orientations, and door control techniques. The efficacy of PPV operation is also enhanced when used in conjunction with wind control device and high-rise nozzle deployment.