One other thing to consider when looking at fire apparatus suction pressure is pressure losses in the LDH to the pump suction. If you have to lay 250- 500 ft of hose from a hydrant with only 5-10 psi, what do you have at the pump suction at the apparatus? You can't assume the hose will be in a perfect straight line.
Craig L. Prahl Fire Protection Group Lead CH2MHILL Lockwood Greene 1500 International Drive Spartanburg, SC 29303 Direct - 864.599.4102 Fax - 864.599.8439 CH2MHILL Extension 74102 [email protected] -----Original Message----- From: Sprinklerforum [mailto:[email protected]] On Behalf Of [email protected] Sent: Monday, December 08, 2014 9:55 AM To: [email protected] Subject: RE: A Poll of the Experienced Absolutely agree with you about the non-value of extrapolating the flow test beyond the observed flow. The part I'm not so sure I would agree with is requiring the 20 psi minimum at the onsite hydrants. The IFC commentary notes that the 20 psi is used because it is the recommended minimum pressure "for fire engine use by the water authorities in order to minimize the possibility of creating a negative pressure in the water main and the resulting damage to the water supply system." Many of the buildings we are involved in require 4,000 gpm. They have private fire loops around the property with usually two connections (with BFP's) to the city water system. Doing the hydraulics flowing 1,000 gpm @ 20 psi for the most demanding four hydrants usually requires a minimum pressure of around 45-50 psi at the city connections. I don't see how taking the pressure in the private fire loop below 20 would damage anything in the municipal system because the pressure would always be above 20 psi at the connection to the city mains. I don't know about the effect on the pumper truck but I think as long as they have water at any pressure they will continue pumping. Ron F -----Original Message----- From: Sprinklerforum [mailto:[email protected]] On Behalf Of [email protected] Sent: Monday, December 08, 2014 6:52 AM To: [email protected] Subject: RE: A Poll of the Experienced Ah, Fire Flow. Now you will gets heads spinning. First, let's start with the basics. There are at least five methods used by various authorities to determine Fire Flow. So if you are dealing with this, be sure Appendix B is the correct method used by the local/state fire authority. Section 507 in the IFC states that Fire Flow is to be determined by an "Approved Method". AHJ will provide or confirm that approved method. Appendix B is not part of the Code and is not always adopted through the legal adoption process, that's why you have to ask, you can't assume. But let's say we're past that and Appendix B is the approved method. The next step is you need to also verify that the local AHJ will permit the flow reduction rate based on sprinklers, do not assume that to be the case. I'm assuming that you might have a warehouse with a fairly high hazard level if you're using ESFR so in cases such as that or where chemicals or other high hazards are present I have had the AHJ deny the reduction. So be sure, don't assume you can apply the reduction. So you've gone down the chart and found your building requires 8000 gpm for 4 hours. The city supply or private fire service system needs to be able to provide that flow and duration to the fire loop serving the hydrants. A minimum of 20 psi residual needs to be available at every hydrant on the loop. This is will be the suction pressure for pumper apparatus. You can assume that in an event that would require 8000 gpm there will be multiple pumpers connected to multiple hydrants. The other issue when dealing with a municipal supply is make sure they can ACTUALLY supply the demand. I've had too many single outlet flow tests and the testing agency extrapolated the curve to show they can meet the demand. I reject those tests. When conducting follow-up tests involving multiple hydrants, more often than not was it proven that the municipality could not actually flow that much water through their system. Extrapolated tests are worthless. You need real data. So the 20 psi pressure needs to be at the hydrants. Fire flow is the water needed to actually fight the fire through the use of manual hand hose lines. This is totally separate and unrelated to sprinkler flow and hose stream allowance. I was involved with a project for a warehouse where the fire fight lasted 13 hours, needless to say they used a LOT of water. This is one topic where the majority of fire protection engineers and designers have not been educated. It is a Code requirement, not an option as most think. Craig L. Prahl Fire Protection Group Lead CH2MHILL Lockwood Greene 1500 International Drive Spartanburg, SC 29303 Direct - 864.599.4102 Fax - 864.599.8439 CH2MHILL Extension 74102 [email protected] -----Original Message----- From: Sprinklerforum [mailto:[email protected]] On Behalf Of [email protected] Sent: Friday, December 05, 2014 9:29 PM To: [email protected] Subject: Re: A Poll of the Experienced I think I agree with you, but to be very specific, let's assume I'm designing a new building on a greenfield site which is served by a public water system. The building is type V construction, 600,000 square feet and fully protected with ESFR sprinklers. Table B105.2 indicated a fire flow rate of 8000 GPM, reduced to 4000 GPM for sprinkler credit, at minimum 20psi. My question is, WHERE is this 4000 GPM at 20 psi measured? At the city water main connection? Or at the fire pump discharge? Mark at Aero 602 820-7894 > > -------- Original message -------- > From: [email protected] > Date:12/05/2014 8:12 PM (GMT-06:00) > To: [email protected] > Subject: A Poll of the Experienced > > Over this weekend I'd like to ask the opinion of those forumites experienced > in the reading and understanding of the "International Fire Code" on the > topic of "Fire Flow" described in Chapter 5, and further prescribed in > Appendix B. Is the available flow rate and residual pressure referenced, > intended to describe these values of the municipal or private water supply > available to the building site? Or, the minimum output of any fire pump > associated specifically with the automatic sprinkler system in the building? > Any takers? Questions? Clarifications? > Thanks for any answers. > > Mark at Aero > 602 820-7894 > > Sent from my iPhone _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
