I knew this would get some people jumping. Bill-
For years I did the same general thing you propose, but added 20% to account for the increased flow when one does hydraulic calc and included the hose stream. But then I started doing forensic/litigation work and realized that to do anything but a supply calc puts you and everyone in a very sticky spot as you are knowingly violating the code. To Chris and everyone else- I know we really don't want to be designing defensively as it seems wasteful. But having been involved in a number of haz mat type fires, the losses get large...not just the building but the environmental clean-up as well. The insurance folks will be looking to keep people in a case, particularly if you have any insurance cash. See it this way. If you simply do design density x remote area x time to get volume and then do the math to get curb height. You know that you are wrong!! Your capacity is not 20 minutes of sprinkler water. Any attorney worth his salt (I would argue they are worth their weight in dooty) will run his questions this way: (Engineer/designer's answer in CAPS) Mr. Engineer, how did you estimate your containment capacity? YOU ANSWER So, you simply do simple multiplication from the design standard correct? YES Are these your hydraulic calculations? (shows you design documents) YES What is the calculated system demand of this system as you designed it? YOU STATE THE DESIGN FLOW RATE So, 20 minutes of water flow at this rate is xxx. Correct? YES Why is your calculated number larger than the estimated containment capacity? YOU STUMBLE ON THIS and JURY & JUDGE SMELL a PROBLEM Now, Mr. Engineer, Your design calculations, is this the flow rate you would actually expect to come out of this system? NO, YOU EXPLAIN THAT THE DESIGN CALCULATIONS ARE THERE TO PROVIDE A BASIS OF DEMAND AND THAT OUR PURPOSE IN DOING CALCULATIONS IS TO PROVE THAT THE WATER SUPPLY CAN EXCEED THE DEMAND. So, you were aware that the actual water supply would provide even more flow than your design calculations? YES And that water supply would exceed the basis of your containment estimate? YES. JURY SMELLING SMOKING GUN Is there a method you could have performed a full supply calc? YES (your cooked here!) Mr. Engineer, what you have said here today is that you estimated the containment capacity doing a simple estimate correct? YES Yet, when you performed actual design calculations you knew you exceeded your estimated figure correct. YES. Did you advise anyone or change your calculations at this point? NO. NOT GOING WELL FOR YOU... You also stated that there is a method to actually determine the actual flow rate the water supply could provide correct? YES. Did you use this method? NO. The attny will then produce a calculation by some other expert who did a supply calc and will demonstrate how off you were. He'll ask you to look at it and then will ask you if it seems reasonable. He'll corner you on this. GAME SET MATCH...you loose. He/She has successfully demonstrated that 1) you knowingly violated the code and 2) you were a contributing factor in the magnitude of the loss. He can do this by alleging that the overflowing containment caused fire spread. That the overflow caused extension of fire beyond the design area. And that the containment and resulting environmental hazard were yours to protect. Sure, there will be a lot of other mitigating circumstances. But the attny does not have to prove that you are solely responsible. Just contributing and that entitles him and his clients to $$$ from you. Which brings up other issues as well. Your professional liability folks cover errors and ommisions, but based on the testimony above may decide that you were negligent...knowingly making errors. They may not be obligated to cover you. I'll leave that to your attorneys. I told you this would be fun!! Paul Sincaglia, P.E. President Firesafety Solutions, Inc. 440.247.3770 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Chris Cahill Sent: Tuesday, January 16, 2007 9:34 AM To: [email protected] Subject: RE: NFPA 30 (03ed) - curbs Paul, If you are advocating adding reality of D-W formula (or H-W) and a supply calc why not go one step further and add reality of the number of heads that will operate. I would contend if all operate the fire will cause a total loss to the building and the size of the containment should be ridiculously large like 100 times the sprinkler demands, H-W in RA times time and be outside the building. Either a hand full of heads control the fire or master streams come out. That's maybe an exaggeration but small at best. I can probably count on one hand the number of times the exact number of heads calculated operates and the building didn't burn down. Hose demands? That's different! Also when the hose streams come out the supply calc goes down. Want to get really fancy consider the ADD. How much will evaporate before it gets to containment and how much goes back up in the plume? I think just keep it simple unless you have failures. Chris Cahill, P.E. Fire Protection Engineer Sentry Fire Protection, Inc. 763-658-4483 763-658-4921 fax Email: [EMAIL PROTECTED] Mail: P.O. Box 69 Waverly, MN 55390 Location: 4439 Hwy 12 SW Waverly, MN 55390 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Paul Sincaglia Sent: Tuesday, January 16, 2007 7:51 AM To: [email protected] Subject: RE: NFPA 30 (03ed) - curbs How would you determine the "expected discharge" from the sprinkler system. Dewayne Ahhhh...the loaded question!! First, I have to say you should check your local codes. The IFC requires spill control to handle the largest spill plus 20 minutes of suppression water. However, if you have other performance goals you may need to alter this...but keep in mind that the local code will be your minimum. Now, the fun part and the point that will no doubt spawn debate all day. How do you determine the amount of water you need to retain? I've seen two schools of thought with lots of modifications. The first, simplest, and probably the most common method to do this is to perform your normal hydraulic calculations and simply take the total flow rate produced by the design basis and multiply by the code's 20 minutes. This gives you a volume figure (gallons) and then you size the curbs around the containment area to hold it. Some people include the hose stream allowance, some don't....I say you should include it. However, one always needs to remember that our normal means of doing hydraulic calculations does not calculate actual output. So if you use the calculation method above, you are likely only providing 10-15 minutes of containment. Which brings me to the better alternatives...provided your calculation software has the capability and you have accurate water data. Most hydraulic programs can do what is called a supply calculation. It essentially performs a hydraulic calculation that has no safety factor. i.e. what will the water supply actually push though the pipes if the entire coverage area is flowing. Generally speaking this flow rate is 15-20% higher than your demand calc, but can really be all over the place depending upon your water supply and your base sprinkler design. Now, I generally like this method as it makes a lot of sense to people when you explain how you got your answers. However, as the forum has been kicking about for days now...Hazen-Williams overestimates friction losses at higher pipe velocities. For our normal demand calculations this is no big deal as it provides an additional level of safety in our designs. But in the supply mode, particularly at higher velocities, the fiction loss is overestimated, therefore the water discharge gets underestimated as the flow gets artificially choked by the friction inherent in the Hazen-Williams method. For what it is worth, I personally don't think that the errors in the supply calculation using Hazen-Williams is all that big a deal. However, I have never done any studies or seen any data to support that. I just know that my figures are still slightly lower than what the actual output will likely be IF the entire coverage area where to activate AND the water supply remains the same. So that is how I would handle it...Using the supply calculation method. But I am sure that many others have many other opinions. So let the games begin. So that I can salt the wound a bit....If you are the code consultant, how do you estimate the containment required when no one has even started the sprinkler designs yet? I have my method...What is yours? Now for real work... Paul Sincaglia, P.E. President Firesafety-Solutions, Inc. 440.247.3770 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Tom L Sent: Monday, January 15, 2007 6:40 PM To: [email protected] Subject: RE: NFPA 30 (03ed) - curbs Dewayne, So do you have a foam system or not? If you do then curbs without drainage is OK If you have a water only system then u will need drainage with the curbs. Review figure 6.8.5 on page 57 of NFPA 30, 2003 edition, it will indicate IF you need to provide spill containment OR liquid spread control. Curbs are used if you have a closed head foam system to control the spread of the product mixed with the water (section 6.4.2.5). If you have a water only sprinkler system and you have a Class I-IIIA liquid then, you need to provide liquid spread control as per 6.8.5.1. Take a look at FM data sheet 7-29 it has more up to date sprinkler protection requirements then NFPA 30/ 2003 edition. Regards Tom Chubb Insurance >From: "Dewayne Martinez" <[EMAIL PROTECTED]> >Reply-To: [email protected] >To: "SprinklerFORUM" <[email protected]> >Subject: NFPA 30 (03ed) - curbs >Date: Mon, 15 Jan 2007 10:51:03 -0600 > >Section 6.4.2.5 deals with curbs, scuppers, special drains, ect....and >states that "If a drainage system is used, it shall have sufficient >capacity to carry the expected discharge of water from the fire >protection systems and hose streams." >If there is only curbs does this apply since there is technically no >drains? If so, what is the proper way to determine the expected >discharge? >Thanks, >Dewayne > >_______________________________________________ >Sprinklerforum mailing list >[email protected] >http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum _________________________________________________________________ Type your favorite song. Get a customized station. 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