SELECTING PPV BLOWERS
Positive pressure has been around for some time now. The fire service has accepted positive-pressure ventilation (PPV) as one of the most effective methods for removing smoke and for use in salvage and overhaul operations. Many questions are being asked, however, as to which fan or blower is best suited to a department.
While this article will not tell you which blower to buy for your department, it discusses the pros and cons of the various types of blowers on the market.
SHROUD VS. CAGE
I have found that the blowers with a shroud produce a more definite cone of air. The shroud acts as an amplifier, deflecting air in the proper cone shape. These units can be placed closer to the opening for the seal. Test the seal or cone of air before buying a blower. A simple test is to hang pieces of tape at the top and near the bottom of the door and to move the blower back until the strips of tape are continuously blowing to the inside. Mark the spot; try a different blower and mark that spot.
The shroud also is safer in cases of accidents, such as when the blower is knocked over or someone runs into it. Should the blower fall or be knocked off a porch, which can happen, the more protection around the blades, the safer the firefighter will be.
Check the height of the cage from the ground. Air is being sucked up into these units in all directions. The higher off the ground the cage is, the less chance of debris being picked up. Pebbles or small rocks moving through the blower can act as projectiles. Leaves or trash can be picked up and sent through the blower.
SIZE
What size blower should your department buy? Is bigger better? In tests, I have found that for a house of average size (1,000 to 1,500 square feet), a blower that produces 8,000 to 10,000 cubic feet per minute (cfm) of air is sufficient. The bigger blowers overpressure the structure, bringing the heat and smoke back toward the firefighter and forcing heat, smoke, and toxic gases under closed doors. If your department is typical and most of its fires are residential, a 10,000cfm blower is large enough. One person should be able to handle a blower of this size. In most cases, a blower that takes two people to set up is too large. Whether a blower will fit on your truck or in a compartment also should be a consideration.
BLADE
The blade is one of the most important features of the blower, and fire departments should have a piece of equipment that is dependable. Every manufacturer claims to have the best blade. Some blower models have plastic blades. In some cases, plastic blades have disintegrated. These blades are more susceptible to damage from foreign debris or objects coming through the blowers. A small nick or chip on a blade can cause a blower to become out of balance, resulting in the blower vibrating and becoming unstable. Some companies will tell you it’s not the blade’s fault; the blade is doing what it is designed to do. This is probably true. Other companies, however, do not have to defend their blades. The objective is not to have to worry about the blade flying apart should small pebbles hit or a firefighter bump into the unit.
Models with wooden blades require a little more maintenance than those with aluminum blades. Nicks or dents can remove the protective finish from wooden blades. Water then can be absorbed into the wood, and the blade will become unbalanced after a period of time. These blades should be inspected regularly for small cracks or splintering.
Aluminum blades have proven to be reliable and dependable. Remember the extreme temperatures to which blowers arc subjected—from 70°F in the station to 0°F ambient temperature to higher than 1,000°F from the fire. The blades should be made of the best material and should be designed for firefighter safety.
STABILITY
To check for stability, place the blower on a smooth floor and check for vibration and also to see if the blower will move when running full throttle. Some blowers have been know n to move when left unattended. Check the legs and feet of the blowers to see if they are so small that they might sink in sand or soft dirt. Determine also whether someone has to stand behind the unit to keep it from tipping over backward if the top of the blower is touched lightly. Check also to see how hard it is to move the blower when it’s running and how easy it is to adjust the angle of the blower. In some blow er models, you have to reach in front of the blower to adjust the angle; in others, you must extend the legs to keep the blower from tipping over backward. The easier the setup, the better. A firefighter should be able to set the unit down on the ground from the truck compartment and crank the blower without having to make any adjustments. Adjusting the blower should be so easy that it can be done safely at night and while half asleep.
AIR PRODUCTION
To determine how much air actually is being produced, I suggest that the blower be rated by an independent rating agency. Several blowers have been rated by the Air Movement Control Association (AMCA). This rating program is based on technical standards adopted by the industry. The AMCA seal on each unit shows that the unit is certified to produce the advertised cfm ratings.
OTHER CONSIDERATIONS
Muffler location. On some units I tested, the muffler was placed close to the frame. After short periods of time, the frame became too hot to touch without gloves.
Gas tank location. Can it be easily accessed during night operations? Wheels make it much easier to move.
Water application through the blower. We found that this feature in most cases is a w’aste of money. It created a hazard as the firefighters entered the structure, making the floor slipper)’ and wetting the firefighters as they entered the structure. They do not produce enough gpms to absorb the Btus generated by even a small fire.
Engine. For the average department, around a five-horsepower engine w’ould be sufficient. A four-cycle engine is recommended for ease of maintenance and starting ability. Since it takes a two-cycle engine to invert, a two-cycle engine might be a good investment for larger departments having several blowers. Maintaining two-cycle engines is a must. The fuel/oil mixture in the engine and the container of mixed fuel must be changed at least every three months to keep the two-cycle engine operating properly.
Stacking units. These units are satisfactory’ for salvage and overhaul. We have found that most departments are progressive and eventually w ill try to use them on an attack. It takes twice as long for setup and needs two people—and which unit do you crank first? We found that they were easy to turn over and didn’t produce the cfms needed on an individual basis. If your department wants to employ PPV fans during fire attack, I recommend a single blower.
Ease of cranking. Some directdrive blowers are hard to crank in semiawkard places, such as on porches or in tight quarters. I also found that the rope had to be pulled quite forcibly before the blower would start.
Placement and ease of controls. Can you find them in a hurry or in the dark? How many controls does it take to crank the blower? Can the blower’s cfm output be controlled? These factors should be looked into before purchasing a blower.
Dealers. Price should not be the primary consideration. Positive pressure quickly is becoming a very competitive business. Ask questions such as, How long has the company been producing blowers? What type of warranty does the blower have? Be sure you know the people with whom you’re dealing and their background. Consider also whether they’ll be in business 10 years from now. Contact as many dealers as possible and have them demonstrate their products. Ask questions and then decide which blower is right for your department.
Water-powered blowers. I have found that water-powered blowers work well for hazardous-materials or other incidents that need a large volume of air. These blowers can provide more than 33,000 cfm. To get the large volumes of air, truck pressure should be around 300 psi. It generally takes a truck just to run the blower, lor salvage and overhaul, how many firefighters want to put up a minimum of 100 feet of hose (50 feet from the truck to the blower and 50 feet from the blower to the truck)? I found in some cases where PPV could have been used that it wasn’t because of the time it took to set up and break down. Most of these units are lighter, but they also are larger, making it a problem to carry them on a truck. Water-powered blowers also have several other advantages. They produce no carbon monoxide and eliminate the danger of sparking associated with electric smoke ejectors from the haz-mat environment.
For the department looking to use positive-pressure ventilation for salvage and overhaul or maybe as a fire attack tool, the gas-powered blowers are the best overall buy. Remember, the greatest value of positive-pressure ventilation will be seen 20 years down the road when firefighter cancer and cancer-related death rates are reduced in departments using PPV in the salvage and overhaul stages of firefighting. If you are not using PPV in salvage and overhaul, you are way behind the times. Quit placing firefighters in smoke-filled atmospheres when it’s not necessary. It is a proven fact that positive-pressure ventilation can save lives.
