Positive Pressure for a Positive Advantage
Part 3
In Parts 1&2, we overviewed 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 3 of this series, let's turn our attention to the following considerations:
Other types of applications.
When to think about using PPV.
Equipment.
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 used 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 this can be explained as follows:
Depending on the type of fire, concentrations of CO within the range of 500 parts per million (ppm) to 1,200 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 used in place of SCBA. SCBA should always be used when personnel encounter hazardous atmospheres.
Fire Attack
In the past, this operation justifiably elicited a significant amount of criticism and concern. However, PPV has been 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.
Firefighter safety is enhanced.
Similar to other fireground operations, this technique must be used 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 used 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 used.
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 used 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.
Search and Rescue
Currently, there is an interesting debate concerning the viability of using PPV with search-and-rescue operations. It is a fact that PPV has the potential to enhance a search-and-rescue operation and increase firefighter safety. These facts were graphically demonstrated by recent tests conducted by the North Carolina Bureau of Insurance and the United States Coast Guard. However, there is also concern for trapped occupants that may be located between a fire and an exhaust opening, which when combined with PPV, may result in increasing the potential of death to a trapped victim. Although both of these viewpoints have merit, most structure fire victims die from smoke inhalation, not burns. Therefore, victims who may be located between a fire and an exhaust opening (when PPV is initiated) will most likely have died before the implementation of PPV or will be saved by the implementation of PPV as follows:
Victims who are near the seat of a fire will probably have died from heat or contact with the fire. Therefore, although PPV can change the direction of fire and heat towards an exhaust opening, it does not normally contribute to the death of victims near the seat of a fire who are most likely the victim of high heat, contact with flame, or smoke inhalation.
The rescue of victims who are still alive can normally be enhanced by PPV due to the introduction of fresh air (and oxygen). Therefore, the introduction of air (oxygen) will reduce contaminants (carbon monoxide) and increase the percentage of available oxygen, thus improving a victims chance of survival. Additionally, PPV also has the potential to enhance a search-and-rescue operation due to its ability to increase visibility (which will enable search-and-rescue personnel to increase the speed of a search) and reduce the potential for flashover (safety for firefighters and victims).
Dumpater Fires
Each day, the fire service receives hundreds of calls to respond to the common dumpster fire. Interestingly, the extinguishment process is the same today as it was 30 years ago and normally consists of several firefighters dressed in protective equipment (without SCBA) using an attack line to extinguish and overhaul the fire. Although most fire service personnel will wear SCBA on fire attack operations, few wear SCBA on dumpster fires because these incidents are perceived as “only a rubbish fire.” Unfortunately, the contents of the modern dumpster have drastically changed from 30 years ago. The common presence of plastic and fiberglass products, illegal dumping of hazardous materials, and other similar materials that when subjected to fire will produce numerous toxic gases that are extremely dangerous when inhaled.
PPV can dramatically improve the suppression and overhaul phases of dumpster fires by providing a directional flow of pressurized air that can allow personnel to operate on the windward (or upwind) side of the flow of air and away from the deadly products of combustion. This can be easily accomplished prior to initiating suppression operations by placing a blower approximately 8-10 feet away from a dumpster. The pressurized air flow will force the products of combustion away from personnel.
Auto Fires
Similar to dumpster fires, the common auto fire is also generally considered a routine incident that is easily handled on a daily basis by fire service personnel. Plastics and other similar synthetic materials will produce copious amounts of deadly toxic gases when exposed to fire. Unfortunately, many fire service personnel neglect to wear SCBA during fire attack and overhaul operations on automobile fires, thereby inhaling any toxic gases that are present in the smoke. PPV can also dramatically improve the suppression and overhaul phases of automobile fires by providing a directional flow of pressurized air that can allow personnel to operate on the windward side of the flow of air and away from the deadly products of combustion. If PPV is used, the opposing doors on either side of an automobile are opened and a blower is placed about 8-10 feet from the auto, allowing personnel to operate on the windward side of the incident.
Salvage Operations
When defensive operations are initiated, focus should be placed on salvage operations that are designed to specifically save (preserve) an office area (if possible). This may consist of salvage operations designed to protect filing cabinets, computers, and other similar considerations. PPV can assist salvage operations by pressurizing an office area to enhance the following considerations:
Reduce or delay the presence of heat and smoke in an office area.
Improve an office environment and the ability of salvage personnel to initiate appropriate salvage operations.
These considerations can be easily accomplished by pressurizing an office area with standard PPV techniques. Pressurized air can then be used to remove heat and contaminants or using the pressurized air in an office area to delay the encroachment of contaminants from a fire and allow salvage personnel sufficient time to initiate appropriate salvage operations. Remember, if you can save the “accounts receivable” of a business, you will save the business!
Marine and Aircraft
PPV can be effectively applied to marine and aircraft applications due to their similarity to structure fires. If an aircraft is connected to a terminal by a jetway, ensure PPV is directed towards the rear of the aircraft to eliminate forcing contaminants through the jetway and into a terminal.
Miscellaneous
PPV has also proven to be effective in other types of applications such as removing flammable atmospheres (gasoline, natural gas, butane, etc.), and minimizing contaminated atmospheres in some hazardous materials incidents. In these applications, the ability to place blowers away from flammable atmospheres (and in fresh air) enhances effectiveness and operational safety considerations. Of particular interest is the area of rehabilitation, as PPV has been able to reduce the core temperature of personnel (using full protective clothing) engaged in fire-attack operations, and rehabilitation operations that are conducted after a fire is knocked down. Tests by the United States Coast Guard have indicated that the use of PPV has reduced the core temperature of personnel up to five degrees during fire suppression operations, which is significant from the standpoint of endurance and safety! During fireground rehabilitation operations, PPV can lower the ambient air temperature around firefighters approximately 10 degrees, and more than 15 degrees when a light water mist is used with the pressurized air.
WHEN YOU MAY WANT TO THINK ABOUT USING PPV
Remembering that PPV 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 towards 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., 1,500-square-foot, 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 used.
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 overview 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 use a readily available source of pressurized water (i.e., marine applications). However, set-up 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.
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).
21-inch with a 5-h.p. engine has slightly less output as a 24-inch blower with a 5-h.p. 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-h.p. 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.
Chief Mittendorf's newest book, Truck Company Operations, can be purchased by clicking here.
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