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  1. #1
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    Default Fire Dept. Connections - Part Deux

    Sorry for my tardy reply, but I just joined the forum. Since the FDC thread is rather dated, I thought starting a "new" thread on the same subject would be appropriate.

    When planning for FDC operations, one must consider the design of the system - which also involves understanding the codes and standards governing their design and use (NFPA 13, NFPA 13E, NFPA 14, NFPA 25 and NFPA 1620).

    First, the reason for pumping the FDC is two-fold: 1) to supplement the system by allowing the sprinklers to discharge more water to more effectively control and possibly extinguish the fire. 2) to supply the system where the system has operated more sprinklers than designed. Not all sprinklers in the building are designed to operate simultaneously (open sprinkle deluge system - aircraft hangers, transformers, etc.). Only the sprinklers in the design area (1,500 sq.ft., 2,000 sq,ft, 3,000 sq.ft., etc. depending on the hazard being protected.) are calculated for simultaneous operation. This means from approximately 10 sprinklers to 40 sprinklers.

    NFPA 13E provides procedures for using FDC's. However, since fire department operations vary, suppression crews should adapt the recommendations of 13E to suit their own SOPís. The primary recommendation is to pump sprinkler system FDCís at 150 psi (although, 13E does not say whether this the discharge gauge pressure or the FDC inlet pressure). For most systems it wonít matter as the system would require significantly less than 150 psi. Warehouses and other high hazard occupancies are notable exceptions. A warehouse using ESFR sprinklers may require 90 psi at the sprinkler (approx 130 gpm). 12 sprinklers are designed to operate simultaneously. This typically requires a fire pump. Does the pump on your apparatus match the fire pump? Quite conceivably a 1,000 gpm pump will not be able to supply the system. A 1,500 gpm may have trouble too (but the problem may be in getting the water to the pump more than the pump itself - depending on the length and diameter of the supply hose, among other things).

    The FDC typically uses two 2-1/2 inlets and a 4" pipe from the inlets to the underground pipe. The system designers do not calculate the pressure loss in this arrangement. There may be an 8" or 10" underground pipe supplying the fire pump with little pressure loss. The 4" FDC pipe can have as much as 20 psi loss in the 5 ft length (plus inlets).

    Of course most buildings such as office buildings and apartments can be easily supplied by the FDC using the 150 psi inlet pressure. Actually too much pressure can be detrimental to the sprinkler systemís performance. High pressures at the sprinkler discharge can atomize the water preventing the water from penetrating the fire plume.

    The design of standpipe systems can be quite tricky. You would be well advised to read NFPA 14 on the types of supplies for standpipe systems. Not all are dry, not all are supplied by on-site fire pumps. Some must be supplied by fire apparatus (in my opinion, the most reliable method unless, as in a highrise, onsite pump(s) are needed). Part of the preplan (see NFPA 1620) should include a determination of the type of standpipe system and the required flow and pressure at the FDC. NFPA 14 requires 500 gpm at the most remote standpipe with 100 psi at the remote outlet (65 psi, if permitted by the AHJ - typically where solid bore tips are used). This probably will not work well with 100 psi nozzles - hence the advantage of the 75 psi nozzle. Long hose lengths are also problematic. Consider: 100 psi Nozzle + 150 ft of 1-3/4 hose flowing 125 gpm (37 psi) + Hose valve loss (5 psi) + pipe losses (20 psi) + Elevation losses (15 psi) + FDC losses (2 psi) + hose losses (10 psi) = 189 pump discharge pressure. The 75 psi nozzle will save 25 psi, but that will still not get the required pressure to 150 psi. And this does not include the full flow required by NFPA 14 (as much as 1,250 gpm).

    Combined Systems: The design does not consider the simultaneous flow of the sprinkler system and standpipe. I believe NFPA 14 contemplates that some of the standpipe water will be applied to the sprinkler system. There are far too many scenarios to consider here, but if the sprinkler system is over run or there is a pipe break, the standpipe supply will be compromised.

    The bottom line is to fully evaluate all buildings with FDCís. Do not assume that if one system can be supplied that all systems can be supplied. Give special attention to warehouses and other high hazard occupancies (especially where an open sprinkler deluge system is used) Check out the required flow and pressure based on the design. If you have problems, check with Fire Prevention and get them to adopt a local requirement to address your concerns (which doesnít happen overnight as the adoption process can be lengthy).

    Consider using 4, 6, or even 8 inlets on the FDC of high demand systems.

    Consider requiring the FDC to be labeled as to the required flow and pressure (at the FDC). NFPA 13 requires this IF the pressure exceeds 150 psi.

    Consider requiring a fire hydrant within 50 ft of the FDC (common in this area). It allows the pump operator to connect to the hydrant and the FDC without assistance. This can be a plus for departments short on man power (but of course there canít be many of those).

    Consider a field test of existing installations. Since some standpipes have roof top outlets, a field test should be relatively easy. How much hose (length and diameter) can you supply from the fire apparatus?

    Consider pumping at pressures greater than 150 psi. Pipe fittings are rated at 175 psi but are tested at 200 psi for 2 hours during the initial acceptance test. Where design pressures are greater than 175 psi, fittings rated at 250 psi are required. Consider requiring the high pressure rated fittings for systems where it can be determined that you will pump at greater than 175 psi. This means at the design stage and very likely would require a local ordinance or at least an information bulletin to designers describing the issue.

    Consider pumping office buildings and apartments at 100 psi. First in crews can determine if the fire is controlled or extinguished. If needed, they can radio back to the pump operator to raise the pressure. Check the required pressures based on the design to make sure it is less than 100 psi. If the design is not available, check the pressure in the main. If less than 100 psi and there is no fire pump, the 100 psi inlet pressure should be OK.

    And donít get me started on pressure reducing hose valves.

    Sorry for the rambling, but I hope this helps. There is a lot more to this, but time is short. Any ????ís let me know.

    Jim Feld
    Fairfield, CA


  2. #2
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    Default

    Well, a thousand apologies. I should know better than to let the telephone interrupt me when number crunching. The standpipe calculation in my previous post is incorrect. Below are the revised numbers. Of, course there are many scenarios but these show the potential problem with pumping the FDC at 150 psi pump discharge pressure.

    Scenario #1
    100 psi Nozzle
    37 psi 150 ft of 1-3/4 hose flowing 125 gpm
    5 psi Hose valve loss
    2 psi pipe losses (estimate)
    15 psi Elevation losses
    2 psi FDC losses
    1 psi hose losses
    162 psi pump discharge pressure.

    Scenario #2
    Flowing two 1-3/4" hoses with 125 gpm each (Total 250 gpm):

    100 psi nozzle
    37 psi Hose loss (150' of 1-3/4")
    5 psi hose valve
    8 psi pipe loses (estimate)
    15 psi Elevation loss
    2 psi FDC loss
    2 psi hose loss (2 hoses @ 50 ft of 2-1/2")
    169 psi pump discharge pressure

    Scenario #3
    Since the remote standpipe is required to be designed to supply 500 gpm, letís assume two 2-1/2" hose lines (150 ft) flowing 250 gpm each.

    100 psi nozzle
    23 psi Hose loss (150' of 2-1/2")
    10 psi hose valve
    28 psi pipe loses (estimate)
    15 psi Elevation loss
    7 psi FDC loss
    8 psi hose loss (2 hoses @ 50 ft of 2-1/2")
    191 psi pump discharge pressure

    Note: At the maximum 1,250 gpm standpipe flow, the two 2-1/2" hoses from the engine to the FDC (50 ft) would be 42 psi. If 100 ft then the loss would be 84 psi. Hence the need to increase the number of inlets at the FDC.

    I hope I got it right this time. If anyone finds a mistake, please let me know.

    Again, my apologies.

    Jim Feld
    Fairfield, CA

  3. #3
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    Moncton,NB,Canada
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    Default

    H2O
    In your calculations, where do you get the pressure loss numbers for hose valves, pipe loss(estimate),FDC, hose loss? Are they from the NFPA standards or from IFSTA?
    And in your calculations, you are using 15 psi elevation loss...is this simply from your scenario ie fire on the 3rd floor?
    Thanks for the info, Brian

  4. #4
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    Default

    Since my post was so lengthy, I did not include all of the details. It was very astute of you to pick up on it.

    The 15 psi is based on 0.433 psi/ft and represents the elevation difference between the gauge on the pump panel and the nozzle (which could by on or near the floor). Obviously, the higher you go the worse it is. I probably should have used the 4th floor.

    I made an assumption as to the pipe length and fittings. Since I have designed and reviewed many standpipe systems, I used my best judgement considering the late hour when I composed the post. The total length includes the pipe length + the equivalent length of fittings (valves, elbows, tees, etc.).

    If you have a particular standpipe in mind, send me the details: Elevation, pipe diameter/length/fittings etc. Include the details of the standpipe pack. Iíll help you with the hydraulic calculations if you want.

    Jim Feld
    Fairfield, CA

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