Let's take this situation to where there is an engineer of record. Seems to me this highlights the importance of that engineer getting a feel for the water supply and giving to the bidding contractors the most accurate water supply information they can - using the information available and their engineering judgment. There can be a lot of variables that need consideration. The EOR should KNOW if a site has a radically variable static pressure; or if there is potential for large water use by neighboring facilities; or if a small town lowers its tank elevations in winter (reducing static pressures); etc.
Now for you contractors working design-build with no PE as the EOR, you are essentially charged with determining all of this information - and sometimes you are forced to fight what you know is 'right' with the demands of your company's pocketbook (that is, when you delve into the water supply AFTER the contract has been negotiated/awarded). But who are we kidding: most often when there IS an EOR, you are STILL charged with gathering this information - along with the other contractors competing for the job. So you better get the water supply information right - but make sure you're low bid, too... BTW - it's not that you CAN'T extrapolate a flow test to higher flow than your test created. It's just not the best practice. The farther away you extrapolate, generally, the lower the accuracy of the flow/pressure point. So if you extrapolate a 2,000gpm test out to 2,100, you're probably o.k. Just avoid extrapolating to 5,000gpm. Conversely, if you flow more than you're total demand flow, you will know that you are getting as accurate a test as possible (given the tools available). I have seen some engineers reject a flow test like I described (2,000 test for a demand of 2,100). That can be plain silly - especially if the retest is particularly expensive. There should always be room for reason... unless you're dealing with the government - then take no chances. Mark A. Sornsin, PE| Fire Protection Engineer Ulteig Engineers, Inc.| Fargo, NDÂ [email protected] -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Jamey Prentice Sent: Monday, April 02, 2012 2:12 PM To: [email protected] Subject: RE: Flow Test That is also my take on the matter, the standard however does not appear to specifically require this!!! As indicated NFPA 291-2010 4.3.6 states " To obtain satisfactory test results of theoretical calculations of expected flows or rated capacities, sufficient discharge should be achieved to cause a drop in pressure at the residual hydrant of at least 25% OR to flow the total demand necessary for fire-fighting purposes." It does not require the contractor to use whichever demand is greater. In this case all tests achieve a drop of 25% as required by the standard however only one test of the three meets the system demand and only when using "theoretical" numbers extrapolated from the curve. What is to prevent a contractor from only flowing until a 25% drop in residual pressure has been achieved? On small dead end water mains this would be very easy to achieve however it would not provide a good indication of the actual condition or availability at the main. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of C&H Fire - Mike Gallello Sent: Monday, April 02, 2012 2:40 PM To: [email protected] Subject: RE: Flow Test Technically the hydrant flow test should be conducted in accordance with NFPA 291. It's rare anyone does it though, it's the generic static, 1 ports then two ports for a 3 point graph. Look in the back of 13 for Fig A.22.3.4 for the idiot proof method for the flow test data. Beyond this, in 291 there's a line (4.3.6) to flow the total demand necessary for fire fighting purposes. Well, spin that into "sprinkler system demand" values and it's pretty simple. Plot your 3-4 point graph depending on how many points you need to represent your sprinkler demand flow and get an actual curve, not a 2 point line. IE We had a tire storage facility here, approximate estimated gallons for the system demand was around 3000 gpm. We had to static one as usual, but then we had to pop 2 separate hydrants with both 2.5" outlets to simulate the drop in the water system for the sprinkler system demand. Long story even longer, you cannot extrapolate a water supply "curve" from a static and a single residual point - you have to get enough flow out of the hydrants to approximate sprinkler demand flows. At least that's my take on it anyway... -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Jamey Prentice Sent: Monday, April 02, 2012 1:49 PM To: [email protected] Subject: Flow Test We are looking at a project that involves an addition to an existing Institutional occupancy(University)in Ontario Canada. Existing flow tests indicate available flows as follows: Static 68 PSI Test 1-50 PSI @ 223 USGPM Test 2-39 PSI @ 416 USGPM Test 3-13 PSI @ 538 USGPM Existing Hydraulic calculations show a most demanding area calculation for the boiler room requiring 23.1 PSI @ 247.12 USGPM @ BOR plus 250 USPM hose allowance. What flow test results should have been used for this system design? I bet you can't guess what numbers the existing system has been designed too?? I can find nothing that requires the design contractor to use the most demanding curve, If test three had not been performed we would have no real indication of the water available! Can contractors arbitrarily choose curves to meet their design needs, can interpreted points on a graph such as those used in test two be used over real numbers such as those in test three? My gut tells me no, but it seems the wallet once again decides. Thanks in advance. Jamey -------------- next part -------------- An HTML attachment was scrubbed... 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