Chris - if I have a branch line with three 25K ESFR sprinklers and a similarly sized branch line (say it's 3" nominal) with three 5.6K sprinklers, which group of sprinklers will discharge more water at 75psi? Hydrants are supplied by a pipe of fixed size, which has inherent capacity as well as limits. If we accept that the lateral to the hydrant has an absolute maximum capacity, then the number of open ports won't facilitate more flow. But within that threshold, if there are two 4" ports then it affords the FD some options, such as taking 2,000 gpm (or more) from one hydrant without needing a high residual pressure to do that, whether it's one or two or three engines. My references to strategies and hydrant types was intended to be in that context.
The point of site and infrastructure planning is, in part, to allow for as many eventualities as possible, which include some of what you allude to toward the end of your comment. Hydrants get damaged, aren't regularly maintained, can be obstructed countless ways, etc., etc. "Overdesigning" fewer hydrants proves a more demanding condition hydraulically and may be the only option if a site that requires 4K GPM only has three hydrants for whatever reason. SL -----Original Message----- From: Sprinklerforum [mailto:[email protected]] On Behalf Of Cahill, Christopher Sent: Monday, December 08, 2014 10:37 AM To: [email protected] Subject: RE: A Poll of the Experienced "If you have two 4" ports you can take a LOT of water from that hydrant at modest residual pressures." Huh? The number/size of openings don't have a correlation to the residual pressure. You are still stuck with the same curve of the available water supply. What you said is if I put in 6" connections I'd get more water at the same residual vs. 4"? That's the way I read it anyway. I can almost say universally you don't get any more water out of a hydrant with 2-4" connections than 2-2.5" plus 1-4". The amount of water one can get out of a single hydrant is more limited by the fire truck connected to it. The only real exception is if two trucks connect to the same hydrant. Then 2-4" would be better but I'd bet not by a lot. IOW 10,000 gpm won't practically go through a 1,500 gpm fire truck. And fire flow provided grows with arriving trucks. In most cases the next truck goes to the next hydrant up the street to get more water. Otherwise, in most cases you have to shut down the first hydrant to connect the second truck. Are there exceptions, sure, a lot of varying scenarios. For example, you could run out of hydrants in practical proximity, some departments may be able to afford 4" valves they hook to the hydrant before they turn it on to allow a second connection if necessary, or things are burning down anyway and stopping flow to connect a second hydrant is NBD. Chris Cahill, PE* Associate Fire Protection Engineer Burns & McDonnell Phone: 952.656.3652 Fax: 952.229.2923 [email protected] www.burnsmcd.com *Registered in: MN Proud to be #14 on FORTUNE's 2014 List of 100 Best Companies to Work For -----Original Message----- From: Sprinklerforum [mailto:[email protected]] On Behalf Of Steve Leyton Sent: Monday, December 08, 2014 12:11 PM To: [email protected] Subject: RE: A Poll of the Experienced Mark: I want to clarify/expand on my answer from last Friday in which I mentioned four or up to four flowing hydrants in your theoretical 4,000gpm demand scenario. As Galen said (and I emphasize), it's up to the AHJ. We are currently working a project with that very flow rate and the AHJ wants to see four flowing. Since we only have three on-site, we're flowing those plus one public FH in the adjacent ROW. I responded a little too succinctly and let the spec's for this particular project leak into the narrative as if it's a widely accepted practice, which it may or may not be. To reiterate Galen's point, the AHJ may want to see 1,000 per FH, or allow up to 1,250 or even 1,500 depending on: 1) That agency's strategies and practices. 2) The type of hydrants required by that agency. More and more we're seeing so-called super-steamers with 2-4" ports. If you have two 4" ports you can take a LOT of water from that hydrant at modest residual pressures. 3) The physical attributes of a particular site. The fire code says that you calculate the table values based on area and construction type of the largest building on the subject site. Appendix B also says that you can reduce the required flow by up to 50% as approved by the AHJ for sprinklers in one- and two-family dwellings and up to 75% for other buildings. At least in CA, we don't see 75% anymore; it's pretty uniformly enforced as up to 50% but we have a couple of twists here and there. One agency in San Diego County doesn't allow any reduction at all and I've worked for a couple that only allow 25% for Type V construction. We amend the code so much here that I'm not sure what's what in the 2013 IFC, or if in contains Appendix BB. In the CA Fire Code, that's a separate appendix for School buildings. I'm assuming that IFC has Appendix C, which is the distribution matrix for hydrants - it tells us how many hydrants have to be available to a building based on the required fire flow. That appendix also tells us that a hydrant must be provided for every 1,000gpm or fraction thereof, hence my answer of four hydrants to your scenario question. So when laying out a site for access and fire flow, you "flow" from Chap 5, to Appendix B (or BB) to Appendix C. SL _______________________________________________ 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
