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 firstname.lastname@example.org.
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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 18.104.22.168.1, 2007-2016 22.214.171.124).
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 126.96.36.199.2.3, 2007-2016 188.8.131.52.2.3.):
Trapped Sections between 5 and 50 gallons (20 - 200 L):
Trapped Sections 50 gallons (200 L) or more:
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“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: 184.108.40.206 and 220.127.116.11). 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 18.104.22.168 (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.22.214.171.124 and A.126.96.36.199, 2019 A.188.8.131.52).
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.184.108.40.206, 2007-2016 Annex A.220.127.116.11, 2019 A.18.104.22.168).
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.
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.22.214.171.124, 2019 A.126.96.36.199). 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:
Design Challenge #1 Winner
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
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Vote Now: Design Challenge #1
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
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.
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Joe Meyer, PE, is a Fire Protection Engineer out of St. Louis, Missouri who writes & develops resources for Fire Protection Professionals. See bio here: About