Positive Pressure for a Positive Advantage – Part 6

WHEN YOU MAY WANT TO THINK ABOUT USING PPV

Remembering that PPV (Positive Pressure Ventilation) is not applicable to every incident, personnel should evaluate each incident in concert with their experience to determine the suitability of PPV for a specific application. When evaluating the various applications of PPV, the following considerations should be evaluated:

Balloon Construction

Balloon construction can allow the unrestricted vertical travel of fire through a wall into an attic. The application of PPV can enhance this process if an exhaust opening is not opened prior to initiating PPV. However, if an exhaust opening is created prior to implementing PPV, most of the pressurized air will flow toward the exhaust opening (path of least resistance) and will have little impact on enhancing fire spread in open walls.

Attic Fires

The implementation of PPV in structures with attic fires should be evaluated in combination with the presence and size of attic vents. If fire has extended into an attic with attic vents that are of sufficient size to allow a significant flow of pressurized air that can spread fire, PPV should not be used unless attack lines are in place. However, the absence of attic vents will normally allow PPV to pressurize a structure (and attic) without spreading an existing attic fire.

Location of Fire

When the location of a fire is unknown, the use of PPV (particularly on fire attack operations) should be carefully analyzed. If a structure is small and relatively simple (i.e., 1500 sq.’ single-story, single-family dwelling), the success of using PPV to exhaust contaminants or enhance fire attack operations is greatly increased due to the simplicity of the structure. However, as the size and complexity of a structure (and fire) is increased, so is the potential of an unsuccessful PPV operation.

Vent-Entry-Search (VES)

When considering the principle of VES, remember that this can be an extremely dangerous operation and is only used by a few fire departments in the United States. The use of PPV in conjunction with VES or Outside-Ventilation-Man (OVM) operations can increase the danger of this operation unless the application of PPV is carefully coordinated with a VES operation. If VES operations are to be conducted with PPV operations and VES personnel are near or between the fire and ventilation opening, VES personnel should conduct their search and exit the structure before PPV operations are initiated. This operation requires coordination and communication between PPV and VES personnel.

Search and Rescue

PPV should not be used (or should be carefully evaluated) for search and rescue operations as follows:

When a VES (OVM) operation is being utilized.
If the Incident Commander has any doubts regarding the implementation of PPV.

In any case, the decision to use PPV to enhance a search and rescue operation must be carefully evaluated for safety, incident conditions, and the amount of time necessary for implementation.

Trench Rescue

The flow of pressurized air can dry the earth, increasing the chances of collapse.

EQUIPMENT

Before we conclude this PPV series, let’s review some basic equipment considerations. When selecting a blower, evaluate the following considerations:

Performance

Performance is measured in cubic-feet-per-minute (CFM). Ensure comparable blowers are rated by the same method as advertising claims can be very misleading.

Size

Factors that should be considered include the CFM necessary for a specific application in concert with the exterior dimension and weight of a blower. Remember that a blower must be stored and carried to the appropriate location by personnel.

Power

Water powered blowers can effectively utilize a readily available source of pressurized water (i.e., marine applications). However, setup time can be a limiting factor.
Electric, water, and hydraulic blowers require an external power source for operation. Generally, electric blowers will not produce the CFM of comparable sized water and gasoline powered blowers. However, the new electric blowers with digital motors are very close in CFM to gasoline powered blowers and feature less weight, lower purchase price, and no carbon monoxide considerations.
Gasoline powered blowers offer numerous horsepower-CFM options with minimal set-up considerations.

Weight

Remember, a blower must be lifted, carried, and placed into operation by personnel.

Water Injection

Water injection has not proven to be consistently effective in fire suppression operations, but has proven to be very effective in rehab operations.

Summary

To summarize equipment considerations, allow this author to make a recommendation. If you do not have specific needs and it was necessary to purchase one blower, the most practical blower would be comprised of the following factors:

Gasoline powered blowers offer a large selection of power and size choices in concert with minimal set-up time. Remember, exhaust tube extensions eliminate C0 being introduced into a structure-confined area (versatility). Additionally, electric blowers do not produce carbon monoxide!
21-inch with a 5 hp engine has slightly less output as a 24-inch blower with a 5 hp engine (performance), and is about the same size as an 18-inch blower (storage requirements). This configuration would be adequate for most single family dwellings and commercials of moderate size.
The combination of a 5-hp engine with a 21-inch fan can be easily handled by one person (weight).
A “shrouded or enclosed” blade will offer the following advantages:
- If a blade fails, the shroud will offer safety for personnel.
- A shroud can prevent the blower from inhaling loose debris (rocks, sticks, leaves, snow, etc) on the ground and ejecting the debris with the pressurized air.
- Although there are a variety of acceptable blades, an aluminum blade has proven to offer minimal maintenance with good longevity.

CONCLUSION

Looking into the future, positive pressure equipment will continue to improve in performance and versatility enhancing its adaptability to current and future applications. The use of this technique is only limited by initiative in concert with resourcefulness, and will only achieve maximum results through diligent training and judicious implementation. However, the most significant benefit of PPV is firefighter safety that will enhance the longevity of the modern firefighter.