Positive Pressure Fans

By Author: Susan Terlitski
Total Articles: 57
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The Positive Pressure Blower is a high volume fan use to pressurize a burning structure, in case of fire, in order to force the smoke out. Positive Pressure Blowers are portable, gasoline powered fans, most of which utilize a 5.5 horsepower engine. The theory of positive pressure ventilation is based on the principal of even pressure distribution. Once a structure is pressurized, air and smoke can be forced out through any opening (similar to escaping from an inflated baloon).

Electric smoke ejectors (negative pressure ventilation) can be used for smoke removal but this has proven to be inferior to positive pressure ventilation.

What makes Positive Pressure Ventilation superior to negative pressure ?

* The risk of injury from the engaged structure is reduced while placing the fan in operation.
* Positive pressure ventilation is faster to set up and requires fewer personnel.
* The Positive Pressure Blower has a self contained power source, while electric fans require cords and adaptors.
* Smoke and heat is removed from all levels of the structure unlike negative pressure which can result ...
... in localized extraction.
* Quicker results. After initial knockdown, positive pressure ventilation can be initiated and will show immediate improvements in the interior conditions.
* It allows replacement of contaminants with vital cooler, cleaner air - especially in sealed or windowless buildings. It's also very effective in large and compartmentalized buildings, warehouses, schools, etc.
* Quick results allow firefighters faster entry due to lower heat levels and improved visibility.

The following criteria should be considered for effective use of Positive Ventilation:

- The cone of air must cover the intake opening. The fan must be placed the correct distance from the structure such as that the cone of air forms a seal around the opening.
- The size and location of the discharge is important. The discharge, if at all possible should be as high and far away from the intake as is practical. The discharge size should be between 3/4 to 1/2 times the intake. This may not always be possible as the fire may have already dictated discharge locations and sizes; but whenever there is a choice, the above criteria should be used.
- It is important to control the ait flow between the intake and discharge. Positive pressure ventilation can move air long distances if proper control is maintained by opening and closing doors, windows, etc. It is important that firefighters understand not to open the structure too much: ie breaking windows, etc.

The standard features of Canada Blower Positive Pressure Ventilators include: fold down "T" handle; 8" pneumatic tires with full width axle; a "tilt and lock" device that allows the unit to be angled 20 degrees up or down with infinite positions in between; sturdy and light 1 inch wrap around frame. Explosion proof electric motors are available as drivers too.

The optimum ventilator placement distance on most 6'6" doors is about five to six feet away. If placement is too close, the seal won't be achieved. If placement is too far away, the cone of air will be hitting well outside the opening.

Additional information can be found at the Canada Blower company web site http://www.canadablower.com/fans/index.html.

Susan Terlitski
Canadian Process Air Systems Designer
Canada Blower
http://canadablower.com/hvac/index.html
http://canadablower.com/blowers/index.html

The Positive Pressure Blower is a high volume fan use to pressurize a burning structure, in case of fire, in order to force the smoke out. Positive Pressure Blowers are portable, gasoline powered fans, most of which utilize a 5.5 horsepower engine. The theory of positive pressure ventilation is based on the principal of even pressure distribution. Once a structure is pressurized, air and smoke can be forced out through any opening (similar to escaping from an inflated baloon).

Electric smoke ejectors (negative pressure ventilation) can be used for smoke removal but this has proven to be inferior to positive pressure ventilation.

What makes Positive Pressure Ventilation superior to negative pressure ?

* The risk of injury from the engaged structure is reduced while placing the fan in operation.
* Positive pressure ventilation is faster to set up and requires fewer personnel.
* The Positive Pressure Blower has a self contained power source, while electric fans require cords and adaptors.
* Smoke and heat is removed from all levels of the structure unlike negative pressure which can result in localized extraction.
* Quicker results. After initial knockdown, positive pressure ventilation can be initiated and will show immediate improvements in the interior conditions.
* It allows replacement of contaminants with vital cooler, cleaner air - especially in sealed or windowless buildings. It's also very effective in large and compartmentalized buildings, warehouses, schools, etc.
* Quick results allow firefighters faster entry due to lower heat levels and improved visibility.

The following criteria should be considered for effective use of Positive Ventilation:

- The cone of air must cover the intake opening. The fan must be placed the correct distance from the structure such as that the cone of air forms a seal around the opening.
- The size and location of the discharge is important. The discharge, if at all possible should be as high and far away from the intake as is practical. The discharge size should be between 3/4 to 1/2 times the intake. This may not always be possible as the fire may have already dictated discharge locations and sizes; but whenever there is a choice, the above criteria should be used.
- It is important to control the ait flow between the intake and discharge. Positive pressure ventilation can move air long distances if proper control is maintained by opening and closing doors, windows, etc. It is important that firefighters understand not to open the structure too much: ie breaking windows, etc.

The standard features of Canada Blower Positive Pressure Ventilators include: fold down "T" handle; 8" pneumatic tires with full width axle; a "tilt and lock" device that allows the unit to be angled 20 degrees up or down with infinite positions in between; sturdy and light 1 inch wrap around frame. Explosion proof electric motors are available as drivers too.

The optimum ventilator placement distance on most 6'6" doors is about five to six feet away. If placement is too close, the seal won't be achieved. If placement is too far away, the cone of air will be hitting well outside the opening.

Additional information can be found at the Canada Blower company web site http://www.canadablower.com/fans/index.html.

Susan Terlitski
Canadian Process Air Systems Designer
Canada Blower
http://canadablower.com/hvac/index.html
http://canadablower.com/blowers/index.html