When are fire sprinkler volumes important?

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):

• Not required to meet any water delivery time to inspector's test connection (NFPA 13 2002 A.7.2.3.1, 2007-2016 7.2.3.3).

Systems between 500 and 750 gallons (1900 - 2850 L):

• Not required to meet any water delivery time when a quick-opening device is provided (NFPA 13 2002 A.7.2.3.1, 2007-2016 Section 7.2.3.4).

Systems over 750 gallons (2850 L):

• Subject to water delivery times (NFPA 13 2002 11.2.3.9, 2007-2016 Table 7.2.3.6.1, below):

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:

• Must serve no more than 1,000 sprinklers (NFPA 13 2002 7.3.2.2.1, 2007-2016 7.3.2.2)

Double-Interlock Systems of 500 gallons or less (1900 L):

• Not required to meet any water delivery time to inspector's test connection (NFPA 13 2016 7.3.2.3.1.1).

Double-Interlock Systems over 500 gallons (1900 L):

• Subject to water delivery times (NFPA 13 2002 7.3.2.2.3, 2007-2016 7.3.2.3.1 and Table 7.2.3.6.1, above)
• System size based on calculating water delivery (NFPA 13 2007-2016 7.3.2.3.1.4)
• listed quick-opening devices are permitted to help meet trip-time requirements (NFPA 13 2007-2016 7.3.2.3.2)
• Note: NFPA 13-2002 Edition only requires water delivery times for systems 750 gallons or greater (NFPA 13 2002 7.3.2.2.2 and 7.3.2.2.3) 

Dry and Pre-Action System Drainage

Auxiliary Drain Location:

• must be accessible where located in areas subject to freezing (NFPA 13 2007-2016 8.16.2.5.3.1)
• where maintained at freezing temperatures, must be minimum 1-inch and accessible with plug or nipple and cap (NFPA 13 2010-2016 8.16.2.5.3.2)
• locations and number of drains must be identified at the dry pipe or preaction valve (NFPA 13 2007 8.166.2.5.3.6, 2010-2016 8.16.2.5.3.7)

Trapped Sections less than 5 gallons (20 L):

• minimum 1/2-inch valve with a plug or a nipple and cap (NFPA 13 2002 8.15.2.5.3.1, 2007-2016 8.16.2.5.3.2)

Trapped Sections more than 5 gallons (20 L):

• provide auxiliary drain with drum drip leg in accessible location, see figure above (NFPA 13 2002 8.15.2.5.3.3, 2007-2016 8.16.2.5.3.5)
• where multiple trapped branch pipe occurs, minimum 1-inch tie-in drains shall be provided and sloped at 1/2-inch per 10-feet (NFPA 13 2002 8.15.2.5.3.4, 2007 8.16.2.5.3.5, 2010-2016 8.16.2.5.3.6)

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.):

• auxiliary drain with nipple and cap or plug not less than 1/2 inch in size
• removal of a single pendent sprinkler allows for drainage of the trapped section of pipe
• an auxiliary drain with flexible coupling or other easily separated connection

Trapped Sections between 5 and 50 gallons (20 - 200 L):

• Minimum 3/4-inch auxiliary drain with valve and plug or nipple and cap (NFPA 13 2002 8.15.2.5.2.2, 2007-2016 8.16.2.5.2.2). 

Trapped Sections 50 gallons (200 L) or more:

• Minimum 1-inch auxiliary drain pipe to accessible location (NFPA 13 2002 8.15.2.5.2.1, 2007-2016 8.16.2.5.2.1).
• Annex material notes that a typical accessible location would be a valve located 7 feet above floor level to which a hose could be connected to discharge water (NFPA 13 2002 A.8.15.2.5.2.1, 2007-2016 A.8.16.2.5.2.1).

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