Understanding Positive Pressure Ventilation:
Firefighters involved in PPV are suggested to study and understand fluid flow to understand Positive Pressure Ventilation.

  • Always remember, pressure is required to drive ventilation.
  • Once pressure is available, a Flow Path must be established to control ventilation.
    • When defining a Flow Path imagine opening and closing specific doors and window as increasing and decreasing resistance to control the Flow Path.
  • Imagining a maze with gates is a good way to understand more involved fluid flow. 
    • Lifting various gates in the maze will allow a fluid to follow different paths.  Opening and closing gates will affect the Flow Path.
    • As various windows or doors are opened, air will flow through.
      • Large gates/outlets will allow more air through. 
      • Small gates/outlets will restrict flow.  More pressure will be required for equivalent flow.
    • Fluids will follow the path of least resistance.
      • Short and wide pathways that are direct will provide the least restriction.
      • Long paths with multiple gates and narrow pathways will increase restriction.
        • Added restriction will reduce fluid flow through a given path.

Define the Flow Path:
To control the flow of air through a structure define the Flow Path/Paths of desired air flow.

  • Identify the desired/available ventilation path (which rooms, hallways, etc. need to be ventilated)
  • Identify the ventilation point.  Smaller outlets will require more pressure for ventilation. (window/door)
  • Identify pressurization point to drive air into the structure (door or window)

Ventilation Sequences may be used to quickly evacuate specific points in the structure.

  • Ventilation Sequences are uses to clear a structure area by area.
    • Opening and closing specific doors and windows will redirect the flow path.
    • Flow paths can be redirected to sequentially clear specific parts of a structure.
    • The maze flow concept will help with this exercise.
  • To add fans, identify additional points of pressurization to drive air into the structure (door or window).
    • Note:  It is not recommended to use high pressure fans with low pressure fans when structure pressure is high.  Low pressure fans will not increase flow through the structure, they are more likely to act as a restricted outlet.

Understanding BlowHard Technology:
The BlowHard BH-20 design is based on a Jet Stream PPV approach :

  • A high velocity jet stream penetrates deep into the structure to build pressure
  • Higher internal pressure drives ventilation to cool and clear the structure

BlowHard just Blows Harder and…yes that matters.  The following are studies conducted at the BlowHard engineering facility in Albany, Oregon.


Battle of the Fans

Battle of the Fans tested CFM vs Pressure between the 21-inch competitors fan our 20-inch test fan.  Two doors in the shop were opened and both fans were turned on.  The fans blew into the structure, and the structure pressure increased.  The competitors fan reached its pressure limit and the pressure generated by our test fan continued to build pressure.  The pressurized air inside structure stalled the jet stream at the door of the competitors fan.  A significant volume of air began blowing out the top and bottom of the door the competitors fan.

Positive Pressure Flow Test

Please download our Positive Pressure Flow Test sheet