Positive pressure ventilation (PPV)

Smoke and heat always move from higher pressure zones (burning apartment) to lower pressure zones (such as stairwells, public hallways, and other parts of the structure). This is called the "flow path." But if we increase the pressure inside the stairwell so that it is greater than the pressure created by the spread of the fire, we can reverse the flow path and contain the fire. This increased pressure is called "positive pressure." This positive pressure is created by deploying PPV fans at the proper location and in the proper positions. This video demonstrates the efficacy of this tactic in mitigating the wind-driven spread of heat and smoke. Without the use of PPV, you will observe that the smoke and heat enters into the stairwell. When a firefighter activates the PPV fan, the positive pressure created by the fan pushes the smoke back into the hallway of the fire floor, increasing visibility, and reducing the temperature inside the stairwell.