Estimating Pipe Sizes for Sprinkler Systems
Occasionally when designing fire sprinkler systems I'm interested in approximately sizing a specific run of pipe early in a project. That point of interest is often an underground service entry, a main for coordination, or even standpipes. Prior to doing a complete set of hydraulic calculations, running a quick calc using the Hazen-Williams formula can help give an order of magnitude pressure loss that is helpful with initial sizing. Here's the calculator I use for these estimates. Don't see the tool below? See it here. Example: Underground Service Main Sizing Consider a new project with an Ordinary Hazard Group II fire sprinkler system. What should the underground service size be? A 4-inch fire main can be permitted under special circumstances (see NFPA 13 2002 Section 15.1.3, 2007-2010 23.1.3, 2013-2016 24.1.3). A 6-inch fire main is common. Is an 8-inch necessary? If the length of the service main is 10 feet, my answer can often be quite different than if the service main is 1,000 feet. For this exercise I often run a quick calculation to judge the pressure loss in this single pipe as opposed to running calculations for a full system, to get order of magnitude pressure loss. Let's assume a long service main length of 750 feet. Hazen-Williams Formula NFPA 13 stipulates the Hazen-WIlliams formula be used for pipe friction loss calculations for systems other than antifreeze (NFPA 13 2002 Section 14.4.2.1, 2007-2010 22.4.2.1, 2013-2016 23.4.2.1). The Hazen-WIlliams formula, while generally considered conservative, only requires the flow, friction loss coefficient (or C-Factor), and the actual internal diameter of the pipe. Estimating Flow for a Sprinkler System For an Ordinary Hazard Group II example, I can roughly estimate the flow for the system simply based on density and area (assuming the density/area calculation approach). A density of 0.20 gpm/sqft over the most remote 1,500 sqft begins to look like:
Approximate Flow = Density x Area x Overflow Rate + Hose Allowance
Approximate Flow = (0.20 gpm/sqft) x (1,500 sqft) x (1.3) + (250 gpm) Approximate Flow = 640 gpm
Why include the Overflow Rate? Naturally a fire sprinkler system is not going to be perfectly balanced.
While my most remote sprinkler can be calculated at exactly 7 psi and it's k-factor that throws exactly 0.20 gpm/sqft, the feed to that sprinkler will have friction loss. Due to that loss, the adjacent sprinkler will experience a slightly higher pressure than 7 psi and thus will throw slightly more water. This process repeats where sprinklers closer to the riser will provide more than the stipulated density. For order-of-magnitude estimates, I've found that a 30% overflow will be generally close to the final flow result. Pipe Schedule The pipe thickness affects the actual internal diameter of the pipe, so I've included it here. I typically will use Schedule 40 pipe for sizes 2-inch and smaller (so that they may have threaded ends), but I've left the schedule type open to users as I know these preferences can vary. C-Factors The C-Factor relates to the friction-loss due to the surface of the interior of the pipe. NFPA 13 stipulates C-Factors for fire sprinkler systems depending upon the type of system and pipe material. These can be found in NFPA 13 2002 Table 14.4.4.5, 2007-2010 Table 22.4.4.7, 2013 Table 23.4.4.7.1, 2016 Table 23.4.4.8.1. Note that important and impactful changes to the c-factors occurred in the 2013 edition for use of galvanized steel, which has been found to accelerate corrosion by focusing the corrosive action at specific weak points in pipe. Friction Losses With only a few inputs (Flow, Pipe Thickness, C-Factor, and Length of Pipe) you'll now have a comparison of pressure loss across a handful of pipe sizes. Punch in 640 gpm, a Global C-factor of 140 for underground pipe, and a 750 foot pipe length to test this example. If there is plenty of water at high pressure available to the site, perhaps a 48 psi drop on the service entry could be tolerable and a 4-inch main could be used where it meets other NFPA 13 requirements. For the vast majority of projects I cover this loss (48 psi) would not be acceptable. The 6-inch service main shows a pressure loss of under 7 psi, and an 8-inch shows under 2 psi loss. Depending on the water to the site, either of these begin to look much more reasonable. The Friction Loss Calculator This tool is designed to give quick-comparisons of pressure loss for a run of pipe and compare it against other pipe sizes. Do you get these free weekly articles? If not, subscribe here. Updated November 2020 I get this question all the time from architects - especially when working around apartment, hotel, senior and assisted living facilities. "Are sprinklers required in the bathrooms?" I don't mind the question at all, because it has a relatively straightforward answer - they're either allowed to be omitted or not. The path to determine whether an exemption applies is actually fairly complex which I'll explore today. Note that this article covers requirements but also some helpful explanatory material pulled in from non-enforceable parts of codes and standards (such as the annex material). Side Note: Big Launch Coming This is week 2 of my 3 part series in creating resources for sprinkler designers, engineers, inspector's, and contractors. Stay tuned for the big product launch coming in the next few weeks. Now back to the article - Why Allow the Omission of Sprinklers in Small Bathrooms? Typically, since bathrooms require regular cleaning and are subject to variable humidity, surfaces can often be ceramic or non-porous. These easily washable surfaces tend to also be less combustible than other building materials. In studies of apartment fires where sprinklers were present, for instance, bathrooms were the area of fire origin in only 1% of total fires and resulted in no civilian deaths, civilian injuries or property loss (NFPA 101 Annex Material in A.30.3.5.4 & A.31.3.5.4). From a risk perspective, small bathrooms present a relatively low risk for fire origin and growth as compared to other areas of a building. Also, bathrooms in buildings with dwelling units also can comprise a major potential additional cost when they are repeated within each unit. Omitting sprinklers can offer a huge cost savings to these type projects. For some residential occupancies, there can be significant cost savings to omitting sprinklers in small bathrooms throughout a building. Due to relatively lower risk of ignition, building codes and standards permit omissions for specific applications. Building Codes Overrule NFPA 13 Starting with the 1997 edition of NFPA 101, language was introduced into the code to override the requirements in NFPA 13 and NFPA 13R. NFPA 101 only overrides NFPA 13 for specific occupancies, which are outlined below. The International Building Code also introduced provisions for omitting sprinklers in restrooms, beginning with the 2015 International Building Code. These sections are also reflected in the companion International Fire Codes. If Small Bathrooms Omit Sprinklers, Is the Building Still Fully Sprinklered? Yes; where NFPA 13 omits sprinklers the building is still sprinklered in accordance with NFPA 13 and is typically considered fully sprinklered. Where omissions are allowed by NFPA 101, the building is also still typically considered to be protected throughout (reference NFPA 101-2015 A.11.8.2.1 or NFPA 101-2018 A.11.8.3.1, for instance). Are Bathtub or Shower Enclosures included in the 55 sqft limitation? Yes; they are typically considered part of the room as NFPA 13R-2002 introductory material clarifies. If There’s Just a Toilet, is it Still a Bathroom? Yes; annex material of NFPA 13 (2002 A.3.3.3, 2007-2018 A.3.3.2) clarifies that a toilet rooms is still considered a bathroom. Also, two adjacent bathrooms are still considered separate rooms provided that they’re enclosed with the required level of construction. If There’s No Door, is it a Bathroom? Weird. This must be some kind of a HGTV renovation for hippy-people if you don’t have a door for some bathroom privacy. Oh and yes, a door is not required in order to omit sprinklers as long as the bathroom complies with the definition of a compartment (NFPA 13 2010-2016 A.8.15.8.1.1). The Quick-Guide to Determine Permitted Bathroom Sprinkler Omissions: Get Access
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Last Week's Survey Results
Last week I sent a survey asking for "challenges associated with sprinkler identification and design selection." I really appreciate the input provided, there was really helpful and great feedback: common challenges people noted in the survey included sprinkler market availability, listing and approvals, field identification, adherence with product data, price, storage limitations, pressure requirements, and spacing requirements. Anticipation for the Big Launch I am very excited to say that I've been developing a live resource over the past couple years to address almost exactly those challenges. Stay tuned, as more details will be available about the launch in a few weeks. In the meantime, I'm also excited that the blog posts over next three weeks (starting with today) will feature tools designed to help streamline and speed workflow for inspectors, designers and engineers. Part I of III: The Cloud Ceiling Calculator This first week covers the relatively new allowances for cloud ceilings.
"Cloud" Ceilings where directly addressed in NFPA 13 beginning with the 2016 Edition
Cloud Ceilings include any ceiling installed in the same plane with horizontal openings to the structure above on all sides (NFPA 13-2016 3.3.5.1). The "cloud" is simply in reference to the appearance that the ceiling "floats". The new provisions in NFPA 13-2016 allows sprinklers to be omitted above cloud ceilings where the gap between clouds (or clouds and walls) meets a maximum allowable dimension based on the floor-to-cloud ceiling height. Backed by Research What I love about this new verbiage is not just that the NFPA 13 committee addressed a specific topic that many had asked about for some time, but that the development of the rules for this section are based on a commissioned project by the Fire Protection Research Foundation. So what is the guidance based on the research findings? Spaces above cloud ceilings do not require sprinklers where the openings have a combined total area of not more than 20 percent of the ceiling, construction feature, or plane used to determine the boundaries of the concealed space and the cloud ceiling arrangement meets Section 8.15.24.1 (NFPA 13-2016 8.15.1.2.1.3). Limitations I've already mentioned that the opening between all cloud ceilings can't be more than 20% of the total room area, but there's a few others that also apply:
Ceiling Spacing Calculator If these limitations can be met, sprinklers may be omitted above where the spacing below the ceiling complies with Table 8.15.24.1. The table addresses the maximum protection area based upon the research, and is a little less than intuitive. Here's a quick calculator that takes your parameters and gathers the appropriate maximum sprinkler protection area (click the link to see the full tool, with a schematic section of the ceiling arrangement): Enter your project parameters in the red highlighted cells to test your situation. Give it tool a try and let us know what you think in the comments section below. If you've found this interesting or helpful, consider getting more of these tools by joining our email group. Already subscribed? Share this on LinkedIn for others who might find it interesting.
Last week I explored when volumes of a system or portion of a system become important. Principally, volume in fire sprinkler or standpipe systems becomes important in overall capacity limitations of dry and pre-action systems and in draining portions of wet, dry, and pre-action systems. See the full article here.
This week I've created a basic quick-and-dirty volume calculator based on the length of pipe in a system (don't see the calculator below? View in your browser here): Simply select the type of pipe used and enter the approximate length of pipe for each pipe size in the system or portion of a system you're evaluating. I created this when looking at whether I break the 5-gallon volume threshold for portions of wet sprinkler systems, bottom legs of standpipes, or overall dry and pre-action system capacities. Email suggestions or tips for improvement to me at [email protected]. Want to see more like this? Subscribe to these free weekly articles here. I'll be posting the weekly article tomorrow but before then I have a question and a favor.
Over the past two years I've been working on a long-awaited resource involving literally hundreds of hours of research and development, but before I wrap up the project I have just one question that will help create a better resource: Learn more and provide input with my quick one-question survey here. It does not necessarily come up often, but the volume of a fire sprinkler system does carry several requirements. Dry and Preaction systems carry water delivery requirements, while all systems carry requirements for drainage. Today I'm summarizing requirements related to when volumes of fire sprinkler systems are important to consider. Dry System Capacity Systems under 500 gallons (1900 L):
Systems between 500 and 750 gallons (1900 - 2850 L):
Systems over 750 gallons (2850 L):
Hazard No. of Remote Sprinklers Initially Open Max. Time of Water Delivery Dwelling Units 1 sprinkler 15 seconds Light 1 sprinkler 60 seconds Ordinary I 2 sprinklers 50 seconds Ordinary II 2 sprinklers 50 seconds Extra I 4 sprinklers 45 seconds Extra II 4 sprinklers 45 seconds High Piled 4 sprinklers 40 seconds Note for Dwelling Units: Dry systems must discharge water in 15 seconds, regardless of system size (NFPA 13 2002 11.2.3.9.1, 2007-2016 7.2.3.1). Inspector's Tests are used to test water delivery times for dry systems when water delivery time test is required. See this article for details and components on inspector's test and drains. Pre-Action System Capacity Single-Interlock and Non-Interlock Systems:
Double-Interlock Systems of 500 gallons or less (1900 L):
Double-Interlock Systems over 500 gallons (1900 L):
Dry and Pre-Action System Drainage Auxiliary Drain Location:
Trapped Sections less than 5 gallons (20 L):
Trapped Sections more than 5 gallons (20 L):
Wet System Drainage
Trapped sections of pipe less than 5 gallons (20 L): One of the following is required (NFPA 13 2002 8.15.2.5.2.3, 2007-2016 8.16.2.5.2.3.):
Trapped Sections between 5 and 50 gallons (20 - 200 L):
Trapped Sections 50 gallons (200 L) or more:
Subscribe & Share Want more like this? Subscribe to our free weekly articles here. Already subscribed? Send to a friend or share on LinkedIn. “Does this canopy need sprinklers?” “Are sprinklers required below the porte-cochere?” “I have a residential balcony; does it need sprinklers?” It's one of the most common design questions in commercial buildings with fire sprinkler systems; you’ve undoubtedly encountered it yourself. The decision isn’t something that is taken lightly, either. In climates where freezing occurs, dry-sidewall sprinklers are often used for shorter-length projections. With new antifreeze systems are not an option (antifreeze must be a listed, pre-mixed solution which is not currently available), larger exterior projections could require dry sprinkler systems with increased cost, maintenance, and greater susceptibility to corrosion. Non-combustible overhangs without combustible storage beneath typically don't require sprinklers, but the process to determine whether sprinklers are required is not always clear-cut. Good Design Judgement Before diving in on whether sprinklers are required or not, remember that good design judgement is always important. Just because certain code verbiage or annex material exists does not mean you, as a designer, engineer, or review authority, should forfeit good judgment or common sense. These are life safety systems and you were blessed with the ability to think analytically for good reason. Soapbox aside; canopies, overhangs, and porte-cocheres provide a unique challenge in that they can compromise a building by (1) subjecting the building to trapped convective heat, (2) radiate heat down to the base of the fire and encourage further growth, (3) provide a continuous fuel path to the building. NFPA 13 addresses exterior projections in Chapter 8 (2002 Edition: Section 8.14.7, 2007-2016 Editions: Section 8.15.7, 2019 Edition: 9.2.3.1 and 9.3.19.1). There are five paragraphs in this section, and while they appear straightforward there are two critical words that tend to throw a figurative wrench into every situation. Two Words that Complicate Everything: “Combustible Storage” NFPA 13 8.15.7.5 (2016): Sprinklers shall be installed under exterior projections greater than 2 ft (0.6 m) wide over areas where combustibles are stored. What constitutes combustible storage? Storage of any item that can burn? What about temporary placement or handling of items – would they not burn in the same fashion that long-term storage would? While not enforceable unless specifically adopted by a jurisdiction, annex material within NFPA 13 offers guidance in interpreting what is considered “combustible storage”. Temporary or short-term items, such as parked vehicles or delivered packages, while combustible, would not be considered ‘storage’ (NFPA 13 2007-2016 Annex A.8.15.7.2 and A.8.15.7.5, 2019 A.9.2.3.2). Minor amounts of combustibles may also not justify sprinklers, such as planters, newspaper machines, or combustible furniture on balconies for occupant use (NFPA 13 2002 Annex A.8.14.7.4, 2007-2016 Annex A.8.15.7.5, 2019 A.9.3.19.2). Temporary loading and unloading of vehicles, according to the Annex material in NFPA 13, doesn't necessarily justify sprinklers. However, good judgement is critical especially when protecting high-priority facilities like hospitals. Justified Situations Conversely, an exterior loading dock is designed to accept incoming shipments which inevitably end up residing below canopies while loading and unloading occurs, even if only temporary. While long-term storage might not occur, it could be reasonably argued that enough shipping items, pallets, boxes, or other items could collect to be considered “combustible storage”. Projections above the only means of egress or exterior ceilings where the building is occupied above is also suggested to require sprinklers (NFPA 13 2007-2016 Annex A.8.15.7.2, 2019 A.9.2.3.2). Either of these arrangements, if not protected, could reasonably compromise the egress ability or occupied areas above and could be justification for providing sprinklers. Parking areas that are not used for pickup and drop-off are another example of combustibles that would be present long-term, which the annex does not exclude. Loading docks are used for transitioning shipments to the building, so collection of combustibles underneath an overhang could be a common occurrence. Judgement by the Designer and Authority Having Jurisdiction (AHJ) If so much of the guidance is provided in the unenforceable annex material and the body of NFPA 13 is vague about combustible storage, how do we determine when sprinkler protection is required? Ultimately, the determination of whether a situation requires sprinklers due to the amount of combustible storage is up to the Authority Having Jurisdiction. It is a judgement call that is based on the amount of combustibles and length of time where combustibles would be present. An Exterior Projection Cheatsheet While the judgement of amount of combustible storage resides with the AHJ, here is an updated and expanded flowchart based on the body and annex material of NFPA 13 to help guide the decision process (original published by the National Fire Sprinkler Association in a TechNotes in May 2007): Get this free, printable PDF quick-guide to Canopy, Overhang & Exterior Projection Requirements here:
Congratulations to Mike, our first ever design challenge winner. Last week Mike's submitted "Design A" was voted the top design running away with 64% of the submitted votes. Congratulations Mike; he climbs to the top of our new leaderboard and earns a $40 gift card towards the online store. See the submitted designs, the challenge, and follow-up discussion about them here. MeyerFire Design Challenge Leaderboard
Have a design challenge you'd like to propose? Send it to us at [email protected]. Which of the following designs do you prefer? We have two chosen finalists for this Design Challenge. Review, vote, and discuss below. Original Design Parameters: Codes: 2012 International Building and Fire Code Standard: NFPA 13 - 2010 Edition System Type: Wet Pipe System, Fully-Sprinklered Seismic: Occupancy II, Design Category B Construction Type: V-B (combustible) Structure: Solid Engineered Joists Pipe Type: CPVC or Black Steel Surroundings: Unit door runs to the common corridor; additional units reside on each side of these units Design A: [View PDFs] Material Comparison: Vote What works and what doesn't? Discuss your take in the comments section on the website. Top designers with highest voted submissions earn a spot on our leaderboard. How would you design it? That's the topic this week with our first Design Challenge. Here's the project parameters for our theoretical setup: Codes: 2012 International Building and Fire Code Standard: NFPA 13 - 2010 Edition System Type: Wet Pipe System, Fully-Sprinklered Seismic: Occupancy II, Design Category B Construction Type: V-B (combustible) Structure: Solid Engineered Joists Pipe Type: CPVC or Black Steel Surroundings: Unit door runs to the common corridor; additional units reside on each side of these units If these units connect directly to a common corridor, how would you layout the sprinkler & pipe, and any accessories (hangers, fittings, etc) in this area? Describe how you would approach it below in the comments section or submit your concept to enter the challenge. You'll get points towards the new design leaderboard just for entering, with top-voted designs highlighted on our site. Be sure to submit your concept by the end of this Friday. Voting Next Week We'll take top designs and post them next week for discussion and voting. These challenges could be a great way to think creatively and learn more about the design and review process. Future Challenges Have a scenario you'd like to propose for a future challenge? Send it to us at [email protected]. Want More Like This? If you haven't already, you can subscribe to these posts here, or forward to a friend who might be interested. |
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+ Unsubscribe anytime AUTHORJoe Meyer, PE, is a Fire Protection Engineer out of St. Louis, Missouri who writes & develops resources for Fire Protection Professionals. See bio here: About FILTERS
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