PRESELECTING PUMP DISCHARGE PRESSURES FOR PRECONNECTED HANDLINES

PRESELECTING PUMP DISCHARGE PRESSURES FOR PRECONNECTED HANDLINES

BY DOUGLAS LEIHBACHER

When pump discharge pressures are not carefully chosen, the nozzle team may at-tempt an aggressive interior attack with an inadequate water supply. This could place the team in danger and render its effort ineffective.

To illustrate the importance of optimal flow, consider the following scenario: Your engine company arrives first-due to a fire in a three-story frame apartment building. Dark brown smoke is showing from the top floor and eaves as you arrive. A ladder company arrives behind your engine and begins to raise its aerial to the roof to effect vertical ventilation. When you step off the apparatus, your lieutenant directs you to stretch a 250-foot 134-inch preconnected handline to the top floor. After donning your SCBA, you walk to the rear of the apparatus. Passing your arm through the top row of extended hose loops, you grasp the nozzle and step back from the tailboard. With this length of hose over your arm, you approach the fire building. A fellow crew member, who will back you up on the line, grabs the second set of long loops and sees that all the remaining hose has been removed from the hosebed. This backup firefighter discards the hose one loop at a time while stretching to the fire floor. In contrast, you carry your folds of hose with you until you reach the fire floor.

On your arrival at the top floor, you en-counter a smoke condition. You remain in the stairwell below the level of the smoke momentarily to don your face piece. With the face piece in place, you begin flaking out the hoseline. As you do, you overhear roof team members on your portable radio reporting that they opened the scuttle and have fire in the cockloft.

Your lieutenant arrives on the top floor along with a forcible entry team and radios the pump operator to start water. As you kneel to one side of the apartment door to bleed the air from the line, you can hear the roof team starting the power saws above. From experience, you know that the vent hole they are cutting will make your job much easier.

When the door is forced open, the hallway becomes charged with smoke, and visibility is lost. As you enter the apartment, you sweep the floor quickly with the hose stream and shut it down. This will cool the floor and remove any sharp debris. After moving in several feet, you encounter severe heat and can see some flame activity in the smoke overhead. Your lieutenant is at your side and orders you to open up the nozzle and aim at the ceiling in front of you to cool the hot gases overhead. When you do, the heat intensifies as the smoke be-comes impregnated with steam. You can hear crashing in front of you as wet plaster falls from the ceiling and hits the floor, re-vealing flames rolling across the cockloft. As you direct the stream upward, the heat continues to build. The line is flexible and easy to maneuver under your arm, but the flames will not darken down, and the punishing heat drives you closer to the floor. In an effort to hold your position, you keep the nozzle moving back and forth over your head. You cannot advance because the flames continue to roll above you. The heat continues to intensify, and your lieutenant orders you to back out. As you exit the fire apartment, you pull the hose back into the hallway and close the apartment door. The interior operation is abandoned, and a de-fensive attack will be initiated outside the building using master streams. As you back the hose downstairs, you wonder what went wrong. You`ve moved in on fires like this before and knocked them right down.

THE CRITIQUE

On returning to quarters after the fire, your lieutenant holds a critique of the operation. During the discussion, the lieutenant asks the pump operator what pump discharge pressure was used to supply the handline. The pump operator answers that the pressure was about 100 psi. The lieutenant reminds the pump operator that 100 psi is needed at the nozzle and that, because of the impact of friction loss and head loss, the nozzle pressure was probably considerably less. He states that he will preplan an initial pump discharge pressure for future operations, which will ensure that the nozzle is supplied with the correct pressure.

THE PUMP OPERATOR

The pump operator is one of the most important individuals on the fireground, regardless of rank. His ability to provide instantly a volume of water commensurate with the amount of fire encountered is the key to successfully containing the fire. Without this expertise, the most aggressive hose teams would be unable to advance. Likewise, search and rescue operations may have to be cut short or abandoned entirely. Remember, a nozzle team is only effective when it has enough water to “overpower” the fire it encounters. When it opens the nozzle and directs its stream into the flame zone, it must penetrate deeply so that the fire will darken down somewhat quickly and allow the team to advance its line farther.

To be a proficient pump operator, it is necessary to understand hydraulic principles. However, the pump operator should not be expected to perform complicated hydraulic calculations during initial fireground operations, which are bewildering enough in their own right. The pump operator has enough to be concerned with in positioning the apparatus properly, shifting into pump, engaging the proper transmission gear, and opening the correct discharges.

PRESELECTING PUMP DISCHARGE PRESSURES

One way to simplify operations for the pump operator, while making conditions safer for crew members operating inside the structure, is to preselect the pump discharge pressures for all preconnected hoselines carried on the apparatus and to mark them for immediate reference. One of the benefits of preconnected lines is that all features except head pressure remain constant; the length of the stretch, the diameter of the hose, the type of nozzle, and even the handle on the pump panel always remain the same. Thus, the friction loss will also remain the same. This makes it possible to determine the optimum pump pressure for each preconnected handline on the engine ahead of time and eliminate the guesswork on the fireground.

The charts shown on page 35 are simple to use and can be used to determine optimal pump discharge pressures for handlines employing 100 psi fog or automatic nozzles. The formula used to develop the charts is FL = 2Q2KL (FL–friction loss; Q–gpm flowing/100; K–conversion factor for hose diameter other than 212 inches; L–length of hose). Figures can vary with the age and make of the hose. They are based on two fundamental hydraulic principles:

1. Friction (FL) varies with the number of gallons per minute (gpm) flowing through the hoseline. As the flow increases, the FL will also increase for a given diameter of hose. For example, if 200 gpm are flowing through a 212-inch line, and that flow is increased to 250 gpm, the FL will correspondingly increase [from approximately eights pounds per square inch (psi) to 11 psi in this example].

2. FL varies with the length of hose stretched. Thus, there would be more FL in a 200-foot preconnect than in a 150-foot preconnect.

To select pump discharge pressures for 134-inch preconnected handlines, use the top chart. To select pump discharge pressures for two-inch preconnected handlines, use the middle chart and for 212-inch preconnects, use the bottom chart. To use the charts, simply choose the desired gpm flow in the column on the left and read across to the pump pressure column on the right, which matches the length of the preconnect on your engine.

For example: If you ride with a 150-foot 134-inch preconnect and want to flow 175 gpm through it, simply locate 175 in the gpm column on the left and read across to the first column on the right, which represents 150-foot preconnects. The needed pump discharge pressure for this flow will be 170 psi.

For engines outfitted with flowmeters instead of pressure gauges, the process is even simpler. It is necessary only to choose the gpm flow you wish in the left-hand column.

When choosing optimal pump discharge pressures as described above, remember that the greater the gpm flow, the better the chance of controlling the fire. [For guidelines on minimum gpm flow for interior structural firefighting operations, refer to “The 212-Inch Handline” by Andrew A. Fredericks (December 1996, page 36).] However, nozzle reaction will increase as well. Thus, consider your staffing level. If too much water is flowing for the number of firefighters assigned to the hoseline, they may be unable to overcome nozzle reaction and will tire quickly.

If, for example, your company responds with 134-inch preconnects and a one-person nozzle crew, 100 to 110 gpm (yielding a nozzle reaction of approximately 50 pounds) may be your optimum practical discharge even though a higher flow would be more effective. In turn, a nozzle crew of two firefighters could handle a nozzle discharging 150 to 160 gpm (nozzle reaction of around 75 pounds), and a three-person hose crew could control an even greater discharge without tiring.

For this reason, it would be wise to field test the pump discharge pressures you have selected with your personnel. In many cases, you will find that an increase in flow is manageable without causing undue strain for the hose team. For the greatest effectiveness, choose the highest flow for which your staffing will allow.

Once you have chosen pump discharge pressures for all preconnected lines, be sure to mark them conspicuously on the apparatus. An ideal location for labeling each pump pressure is on the discharge gauge corresponding to each preconnect. An equally good place to label is the handle of the pump discharge gate for each preconnect. Finally, the inside of the pump operator`s compartment door also provides a handy, out-of-the-way place to list pump pressures.

Lastly, if your company uses constant-flow fog nozzles, be sure to choose a pump pressure within the range of the nozzle`s capacity, and remember to reset the ring on the nozzle to correspond with the chosen gpm flow.

In addition to simplifying the pump op-erator`s job, preselecting pump discharge pressures can also make interior firefighting safer. To advance their lines within the structure, hose teams must discharge enough water to be capable of darkening down the fire they encounter. When there is too much fire to advance, they must have enough water to hold their position to protect search teams. Most veteran firefighters have been admonished never to stretch a booster line into a building fire. The reason for this is the limited discharge capability of a booster line. With only 30 to 40 gallons or less per minute available, a booster will be ineffective within a structure, given the volume of heat and flame likely to be encountered. Yet, stretching a 134-inch line into a structure and supplying it with only 80 to 90 gallons per minute is tantamount to stretching a booster line. There will be times when you will get away with it, but the line will be ineffective when you encounter heavy fire conditions.

Without preselected pump pressures, many pump operators will be impelled to make an educated guess and await further instructions. This is not the best option. The reason is illustrated by an article published recently by IFSTA in its quarterly magazine Speaking of Fire. The article describes a study conducted by the National Institute of Standards and Technology. The study shows that over the past 50 years, the fire load (lbs./sq. ft.) found in residential buildings has more than doubled. Additionally, the use of synthetic materials, such as polyurethane foam, in home furnishings cause hotter, longer-burning fires than did the ordinary combustibles used earlier in this century. Add to these findings the advent of thermal-pane windows, which hold heat in, and it is easy to see why higher flow rates are becoming more essential to controlling structure fires.

Although the amount of fire encountered will vary with the fire loading of each structure fire, the amount of water the hose team can expect for its line should remain constant and not vary from pump operator to pump operator. The optimum pump discharge pressure, then, for an aggressive interior attack should be a standard pressure preselected by the company officer that will make full use of the flow capability of the preconnect being stretched, within the constraints of staffing levels. When only a minor fire condition is encountered, it is the nozzle team`s job to control the amount of water it uses, and the company officer always has the option of directing the pump operator to reduce the pressure. But more importantly, nozzle teams must be confident that they are using their optimal flow in cases when they encounter fire that will not darken down and they cannot advance. This is the time to consider altering tactics.

WATER DAMAGE

It would seem that an increase in discharge would increase the amount of water damage. That is not necessarily the case. In fact, the amount of water damage may actually decline. Having enough water to control a fire with an interior attack eliminates the need to fall back on an outside attack using master streams.

During an interior attack, water must be applied properly. Occasionally, it is applied unnecessarily before reaching the proximity of the fire. Once the fire is encountered, experienced engine companies advance by a series of stops and starts whenever possible. Once the fire darkens down, they shut down the nozzle and move forward to a better position. The faster the fire darkens, the sooner the nozzle can be shut off. In fact, most water damage occurs when the nozzle is kept open long after flames have darkened down. Additionally, during overhaul, steam rising from structural members is often mistaken for smoke and is washed down excessively. This is rarely necessary. Applying water properly and using it sparingly during overhaul are the best ways to minimize water damage.

In summary, preselecting pump discharge pressures for preconnected handlines provides two significant benefits. It simplifies initial operations for the pump operator and improves the fire flow capabilities so that interior hose operations are safer and more effective. It may still be necessary for the pump operator to make adjustments for changes in nozzle elevation (65 psi per story, to overcome head pressure) or reduce pump pressure during overhaul to prevent water damage, but the process will be simplified and the initial flows will be sufficient to effect a quick knockdown more often.




DOUGLAS LEIHBACHER, a 15-year veteran of the fire service, is a captain in the Yonkers (NY) Fire Department. He is a New York state-certified fire instructor.

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