POSITIVE-PRESSURE VENTILATION Some Questions
VOLUNTEERS CORNER
SINCE ADDRESSING the subject of positive-pressure ventilation in the October 1988 “Volunteers Corner,” several comments have been received. As would be expected, there were proponents and opponents of the concept. Several questions were advanced that merit consideration and must be answered before your department contemplates initiating positive-pressure ventilation with a fire attack.
In a multi-occupancy building with an interior corridor, such as in an apartment building, will positive pressure drive the heat and smoke into uninvolved apartments, threatening the occupants? This should not be a problem if the officer is able to make an adequate size-up and proceed with horizontal ventilation from the fire area. Subsequent positive-pressure ventilation (PPV) will force the heat and smoke to follow the path of least resistance, which will be out of the horizontal opening. If the doorway to the involved apartment is left open, PPV should reverse the air flow from into the hallway to out of the selected horizontal vent openings. Actually, this should improve hallway conditions, enabling rescue and escape of people farther down the hall. If the door to the apartment is closed, PPV will clear the hall and reach maximum effectiveness when the door is opened for fire attack.
A similar question has to do with driving heat and smoke into uninvolved areas or into fire personnel working in the building. This again depends upon the proper placement of the fans and the essential need for ventilation ahead of the blowers directly from the fire area. The fans should be placed on the unburned side of the fire, not forcing the heat and smoke in, but using the created horizontal or vertical ventilation and forcing the combustion products out away from firefighters working on the interior. Again, it is critical to establish a path of least resistance to the outside with conventional ventilation techniques.
Will the thermal balance in the fire area be upset and bring heat down on advancing attack crews? If fans of sufficient size are used, all heat and smoke should be forced forward with no churning effect. Rather than circulating the superheated air downward from the ceiling level, PPV will force it out of the structure. Tests have shown room temperature reductions of 400-500° F where this method has been used. This greatly reduces the heat stress to attacking firefighters.
Won’t the fire intensity increase or hidden, smoldering fire ignite vigorously as additional oxygenladen air is forced into die fire? Certainly, these are possibilities—that is the reason the fans must be used for only a short time prior to the fire attack. There must be a quick, thorough fire attack immediately with adequately sized hoselines for the potential fire area. Overhaul must be performed effectively to discover any hidden fire. The benefit is, however, that due to the positive-pressure ventilation, visibility will be greatly improved, heat reduced, and a faster attack accomplished. The earlier extinguishment and subsequent loss reduction should far outweigh any increased fire damage from the momentary air input.
The applications of positive pressure appear to be only for residential structures; what about larger buildings? The concept will work on larger structures; however, more resources (blowers and firefighters) will be needed. Fans may have to be used in series to reach the fire area or in parallel to achieve sufficient air flow.
Positive pressure can be applied to taxpayers or strip shopping centers with a common attic to restrict the fire spread laterally through the attic. This is accomplished by opening the attic access panels in the occupancies on each side of the fire area, checking for fire extension, and—if there is no extension-then pressurizing the attic area from these two locations. The fire will then require vertical ventilation in conjunction with this operation. Obviously, this will require several firefighters and fans. If manpower is critically low, it may not be possible to start PPV to this extent. Regardless of positive-pressure initiation, the attic areas must be .checked early for fire extension outside the fire area.
POSITIVE-PRESSURE VENTILATION
Is positive-pressure ventilation good utilization of manpower? This may come down to the simple question of whether it is better to take a beating fighting the smoke conditions and heat or to take the extra time to set the fans, pressurize, and make an easier, faster, efficient fire attack. Actually, if a department opts to use PPV, it should be included in its standard operating procedures. This would outline when it should be done and how it would generally be accomplished. Good standard operating procedures will save much confusion on the fireground.
Positive pressure is not the panacea of the structural fire problem. There are times for its application, and incidents in which personnel will need to be used for other duties. It is a tool we should have in our fire attack arsenal and be ready to use when the need arises.
Those interested should test the applications and properly train on the procedures prior to use. It may be beneficial to contact other agencies that have run tests or regularly employ the operation. Tests have been conducted by the North Carolina Department of Insurance, Fire and Rescue Division; the Dallas Fire Department; and the Los Angeles City Fire Department. The outcomes reveal lower temperatures, lower carbon monoxide levels, and a significant improvement in salvageable property. These results can make attack easier, assist in rescue of building occupants, and reduce losses.
