I just wanted to take a quick moment and thank you for the great response to this three day launch of the Sprinkler Database.
If you haven't checked it out already - the deal for the Sprinkler Database is here.
I look forward to continuing to create helpful tools to help you do exceptional work, and the launch of the database is one way that helps me keep those efforts going.
Have a great weekend and a Happy Easter, thank you!
If you coordinate upfront bid documents and are planning to have a dry sprinkler system on your project, you probably get the same question from electrical engineers as I do - how large will your compressor be?
It can be a difficult question to answer, considering there's multiple manufacturers and a handful of different options in choosing the right compressor for your project.
NFPA 13 requires that a dry system have an air supply capable of restoring normal air pressure for the system within 30 minutes (NFPA 13 2002-2010 Section 220.127.116.11.2, 2013-2016 18.104.22.168.2).
Fortunately, I've made a small update to the Sprinkler System Volume Calculator that indicates compressor sizes associated with your system volume. See the full tool here.
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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.
NFPA 13 stipulates the Hazen-WIlliams formula be used for pipe friction loss calculations for systems other than antifreeze (NFPA 13 2002 Section 22.214.171.124, 2007-2010 126.96.36.199, 2013-2016 188.8.131.52).
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.
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.
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 184.108.40.206, 2007-2010 Table 220.127.116.11, 2013 Table 18.104.22.168.1, 2016 Table 22.214.171.124.1.
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.
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.
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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.126.96.36.199 & A.188.8.131.52).
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.184.108.40.206 or NFPA 101-2018 A.220.127.116.11, 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.18.104.22.168.1).
The Quick-Guide to Determine Permitted Bathroom Sprinkler Omissions:
Have trouble viewing? See the flow chart here.
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Joseph Meyer, PE, is a Fire Protection Engineer in St. Louis, Missouri. See bio on About page.