Positive Pressure for a Positive Advantage – Part 4

In parts 1, 2, and 3, we reviewed the basic differences between negative and positive pressure ventilation, implementation considerations for positive pressure ventilation, and tactics for pressurizing a variety of structures. If you are familiar with PPV, you know that PPV can be used in a wide variety of applications (other than smoke removal in structures), and is only limited by your initiative, resourcefulness, and appropriate safety considerations. So, in part four of this series, let’s begin to turn our attention to other applications.

OTHER APPLICATIONS

OVERHAUL OPERATIONS

Unless a fire has been totally extinguished and the contaminated structure completely ventilated, overhaul operations are often conducted within varying concentrations of smoke, heat, and fire gases (in fact, when is the last time you conducted an overhaul in a less than perfect atmosphere?). Without appropriate ventilation, heat, smoke, carbon monoxide, and other toxic gases will accumulate during overhaul operations. PPV can be utilized during overhaul operations to provide a flow of fresh-cool air through the overhaul area resulting in the following conditions being improved:

Humidity and radiated heat within an overhaul area is reduced.
Smoke within an overhaul area can be substantially reduced (depending on the degree of extinguishment).
Similar to smoke, carbon monoxide and other toxic gases can be significantly reduced.
Visibility can be improved.

In general, a moderate flow of air is sufficient to cause smoke, heat, and toxic gases within an overhaul area to move in the direction of pressurized air movement. This is normally achieved by running your equipment at partial throttle. A single blower is adequate for an average single family dwelling of 1,800 square feet. Practical experience has indicated that PPV does not have the tendency to accelerate or spread fire that may be in the overhaul area. If fire does begin to accelerate or spread, it can be easily controlled by shutting the blower off, reducing the RPM of the blower, increasing the distance between the overhaul area and the blower, or extinguishing the fire.

An important concern when utilizing gasoline powered blowers for overhaul operations is the introduction of Carbon Monoxide (CO) into a structure, potentially raising the interior levels of CO. At this point, you are probably thinking “I thought PPV reduced CO inside a structure?” PPV can reduce and simultaneously raise the levels of CO inside a structure and can be explained as follows:

Depending on the type of fire, concentrations of CO within the range of 500 parts per million (ppm) to 1200 ppm are easily obtainable during overhaul operations. Measurements during actual overhaul operations have indicated that PPV can reduce CO concentrations of 1,000 ppm to approximately 130 ppm to 220 ppm.
A single gasoline powered blower will introduce approximately 140 to 160 ppm of CO into a structure.
Therefore, if high CO levels are present, PPV will lower the CO levels. If CO is not present or low CO levels are present, PPV can raise the CO levels.

As most departments use gasoline powered blowers, the introduction of CO can easily be eliminated by the addition of tube extensions that attach to the muffler, thereby directing all of the exhaust away from the pressurized air entering a structure.

NOTE: PPV should never be utilized in place of SCBA. SCBA should always be used when personnel encounter hazardous atmospheres.

FIRE ATTACK (PPA)

In the past, this operation justifiably elicited a significant amount of criticism and concern. However, PPV has, and is currently successfully used by numerous departments as an initial fire suppression technique prior to the introduction of hose lines when considering confined fires, and is capable of providing the following results within an involved-confined area:

Smoke and heat are significantly reduced
Visibility is improved
Internal temperatures within a confined area are reduced
Reduced potential for flashover conditions
When water is placed on a fire, the resultant steam is carried away from personnel on the attack line
Enhances firefighter safety

Similar to other fireground operations, this technique must be utilized within the following parameters to ensure a successful operation:

A technical and practical operational knowledge of PPV is essential. You don’t read an article in a fire magazine and then “go for it”!
This technique is most effective when utilized on confined fires
Backdraft (or potential backdraft) conditions must not be present
Blowers capable of at least 7,000 CFM provide the most effective results
Pressurized air from blowers should seal the appropriate entrance opening
The exhaust opening should be placed as close to the seat of a fire as possible. Horizontal (window or door) or vertical (roof openings) exhaust openings can be utilized.

As an example, assume a typical single story, single family dwelling of 1,800 square feet with a fire in a rear bedroom. The structure is charged with smoke and heat:

After arrival of an initial company, an appropriate person circles the structure to determine the location of the fire and a suitable exhaust opening. In this scenario, the proper location of an exhaust opening is a window in the involved bedroom.
When the location of the fire and exhaust opening has been determined, a blower and attack line are placed at the point of entry of attack personnel (front door).
When the exhaust opening, attack line, and blower(s) are ready, the blower(s) should be started and positioned to cover the front door with pressurized air. Ensure the exhaust opening is created first.
With pressurized air traveling through the entrance and exhaust opening, heat and contaminants between the exhaust and entrance opening will immediately begin to be expelled to the exterior of the structure.
After allowing several seconds for the structure to begin to clear, advance the attack line into the structure. Personnel should spend as little time as possible in the entrance opening as this will block or restrict the pressurized air being forced into the structure. The reduced heat, smoke, and improved visibility should enable an improved attack on the seat of the fire. As the fire is knocked down, the resultant steam from extinguishment will be carried away from attack personnel and expelled with the heat and smoke.

Although PPV can be effectively utilized with an attack line in many applications, it cannot be applied to every confined fire. This technique will only achieve satisfactory results through a combination of proper training and judicious implementation.