Research for the fire service: positive pressure ventilation

NIST recently completed a multi-year study on positive pressure ventilation. A wide range of experiments were conducted in different environments, including high-rise buildings, a high school and within the laboratory. The reports all total more than 1,000 pages.  The below article from Fire Engineering focuses on the practical results of the studies.

Positive Pressure Ventilation

Positive pressure ventilation (PPV) is a ventilation technique used by the fire service to remove smoke, heat and other combustion products from a structure. This allows firefighters to perform tasks in a more tenable environment. PPV fans are commonly powered with an electric or gasoline engine and range in diameter from 0.30 m to 0.91 m (12 in to 36 in). More recently, fans up to 2.1 m (84 in) have been manufactured and mounted on trucks and trailers. Typically, a PPV fan is placed about 1.2 m to 3.0 m (4 ft to 10 ft) outside the doorway of the structure. It is positioned so that the “cone of air” produced by the fan extends beyond the boundaries of the opening. With the doorway within the cone of air, pressure inside the structure increases. An exhaust opening in the structure, such as an opening in the roof or an open window, allows the combustion products to escape due to the difference between the inside and outside air pressure. The smoke, heat and other combustion products are pushed out of the structure and replaced with ambient air.

Another use of PPV is to increase the pressure in a portion of a structure by not providing a vent location. This increase in pressure, if adequate, will prevent smoke flow to a “protected” area. This is most useful in larger structures such as schools, hospitals, malls and high-rise buildings.

Read the entire article at

Download the full report at

NISTIR 7213, Effect of Positive Pressure Ventilation on a Room Fire.

S. Kerber and W.D. Walton, National Institute of Standards

and Technology, Gaithersburg, MD 20899, March 2005.