Alternate use for PPV fans
Brad Gould
Lieutenant
Renton (WA) Fire Department
This is in response to Firefighter Richard E. Shea`s letter to the editor in the May 1995 issue regarding the limitations of positive-pressure fans. I have a suggestion I believe would solve the problem presented in his letter [the exhaust from the gas-powered fan increased the CO level in a split-level ranch residence to which the department had been called for activation of a carbon monoxide detector alarm] and other situations that may be encountered.
I suggest the fans be used in a more traditional fashion–negative ventilation. In most situations requiring the removal of light smoke in nonflammable atmospheres (food on the stove, contaminated air, for example), I`m confident most users would find the positive-pressure fan very effective. These fans are capable of moving large volumes of air into, as well as out of, a structure or other confined area. The technique is very simple and effective–simply reverse the fan so it draws air from the contaminated area. It is quite easy to control the air removal simply by opening windows to provide an adequate supply of fresh air, which will be drawn into the structure by these powerful fans as the smoke is removed. It is not necessary to form a cone of air to seal the exit as it is with traditional positive-pressure ventilation. It is most effective if one places the fans as close to the exit point as possible (at the threshold of a door).
This type of negative ventilation with positive-pressure fans is also a way of bringing fresh air into a structure in which positive pressure was used to ventilate heavy smoke conditions. I commonly use this technique to pull fresh, clean air into a previously ventilated area so it can be safely reoccupied by the tenants….