Required Duration for Secondary Water Supply?

7/6/2023

We have a project where window sprinklers are being used as part of a 2-hour Fire Barrier.

The engineer wants the second water source to be enough to run for two hours (that would mean we'd need about 40,000 gallon tanks) in an already-designed building.

Others are arguing that the primary water source needs to meet the listing but the secondary water source can be 30-minutes as that's when the fire department would hook up and operate.

What is the required duration for the secondary water supply?

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6 Comments

Dan Wilder

7/6/2023 08:15:23 am

IBC 2018 - Section 403.3.3 Secondary Water Supply
Only requires the calculated sprinkler demand, including hose stream, for "not less than30 minutes". If your AHJ or an insurance requirement has been modified to require more, then that would supersede....

Ray Hardy link

7/6/2023 08:26:11 am

Are you in a seismic zone greater than category B?

Todd E Wyatt

7/6/2023 08:33:06 am

SUMMARY
The recommended duration for the water supply for the automatic sprinkler system (ASPS) should match the 2-Hour fire-resistance rating (FRR) of the 2-Hour Fire Barrier (2FB) that it is "replacing."

EXPLANATION
The use of an ASPS (active fire suppression system) to "replace" the requirements of a 2FB (passive FRR assembly) is permitted as an "Approved Alternate Method" per the scoping Code (e.g. 2021 IBC) in accordance with Section 104.11. The AHJ (building official) shall approve this "Approved Alternate Method" by reviewing research reports (104.11.1) and possibly tests (104.11.2).

The only prescribed substitution for a Fire Barrier (FB) with an ASPS is for the "Enclosure of Atriums" (404.6) which permits the 1FB to be replaced with a 0-Hour Smoke Partition (0SP) protected by an ASPS on both sides.

REFERENCES
2021 IBC
Chapter 7 Fire and Smoke Protection Features
Section 701 General
701.1 Scope
The provisions of this chapter shall govern the materials, systems and assemblies used for structural fire resistance and fire-resistance-rated construction separation of adjacent spaces to safeguard against the spread of fire and smoke within a building and the spread of fire to or from buildings.

Section 703 Fire-Resistance Ratings and Fire Tests
703.2 Fire Resistance
The fire-resistance rating of building elements, components or assemblies shall be determined in accordance with Section 703.2.1 or 703.2.2 without the use of automatic sprinklers or any other fire suppression system being incorporated, or in accordance with Section 703.2.3.
703.2.2 Analytical Methods
703.2.3 Approved Alternate Method
The fire resistance of building elements, components or assemblies not complying with Section 703.2.1 or 703.2.2 shall be permitted to be established by an alternative protection method in accordance with Section 104.11.

Chapter 1 Scope and Administration
Section 104 Duties and Powers of Building Official
104.11 Alternative Materials, Design and Methods of Construction and Equipment
The provisions of this code are not intended to prevent the installation of any material or to prohibit any design or method of construction not specifically prescribed by this code, provided that any such alternative has been approved. An alternative material, design or method of construction shall be approved where the building official finds that the proposed alternative meets all of the following:
The alternative material, design or method of construction is satisfactory and complies with the intent of the provisions of this code,
The material, method or work offered is, for the purpose intended, not less than the equivalent of that prescribed in this code as it pertains to the following:
Quality.
Strength.
Effectiveness.
Fire resistance.
Durability.
Safety.
Where the alternative material, design or method of construction is not approved, the building official shall respond in writing, stating the reasons why the alternative was not approved.

104.11.1 Research Reports
Supporting data, where necessary to assist in the approval of materials or assemblies not specifically provided for in this code, shall consist of valid research reports from approved sources.
104.11.2 Tests
Whenever there is insufficient evidence of compliance with the provisions of this code, or evidence that a material or method does not conform to the requirements of this code, or in order to substantiate claims for alternative materials or methods, the building official shall have the authority to require tests as evidence of compliance to be made without expense to the jurisdiction. Test methods shall be as specified in this code or by other recognized test standards. In the absence of recognized and accepted test methods, the building official shall approve the testing procedures. Tests shall be performed by an approved agency. Reports of such tests shall be retained by the building official for the period required for retention of public records.

404.6 Enclosure of Atriums
Atrium spaces shall be separated from adjacent spaces by a 1-hour fire barrier constructed in accordance with Section 707 or a horizontal assembly constructed in accordance with Section 711, or both.
Exceptions:
A fire barrier is not required where a glass wall forming a smoke partition is provided. The glass wall shall comply with all of the following:
Automatic sprinklers are provided along both sides of the separation wall and doors, or on the room side only if there is not a walkway on the atrium side. The sprinklers shall be located between 4 inches and 12 inches (102 mm and 305 mm) away from the glass and at intervals along the glass not greater than 6 feet (1829 mm). The sprinkler system shall be designed so that the entire surface of the glass is wet upon activation of the sprinkler system without obstruction;
The glass wall shall be installed in a gasketed frame in a manner that the framing system deflects without breaking (loading) the glass before the sprinkler system oper

7/6/2023 08:36:03 am

If the window sprinklers are being used to create a 2 hour fire rating, than it may be considered a fire separation by the building code you are using so a 2 hour water supply for that area would be required. It may also depend on the window sprinkler you are using. On the Tyco WS cut sheet it states the following:

"Duration of Water Supply
Duration of water supply must comply with requirements of NFPA. If window sprinklers are used to provide the equivalency of a fire rating, the water supply must be capable of supplying water for the required rating period."

I would ask the manufacturer if the water supply has to include the window sprinklers for 2 hours and overhead sprinkler area for 2 hours as well, or does the overhead sprinkler area just need to be as per NFPA, and the windows for 2 hours. I am not sure how the test was performed for the listing, and the overhead sprinklers may be required for the entire 2 hour duration.

Pete H

7/6/2023 08:44:17 am

If it's a high rise of specific seismic categories: It's required, and not less than 30 minutes as per IBC 403.3.3 (2015 Edition).

If it is anything else: There is no secondary water supply guidance, it is to work the same as the capacity and duration requirements for any water supply as per NFPA 13 (2016 edition) 24.1.2 and NFPA 13 (2016 edition) Table 11.2.3.1.2.

Please be advised for extra hazard that does not have waterflow alarm devices and supervisory devices that are electrically supervised and such supervision is monitored at an approved constantly monitored location that the duration as per the table is 120 minutes or two hours. Your AHJ could view the window sprinklers creating a 2 hour fire barrier as extra hazard perhaps? But your best argument (imo, I could be entirely wrong about this, it has happened before) would be trying to argue your hazard and duration for water supply requirements as per that table.

Jesse

7/6/2023 08:56:32 am

Typically, in the LH occupancy water supply duration is indeed calc'd at 30 miin. But I think the 2 hour duration here is being derived as the sprinklers are used in place of the 2 hour fire barrier.

Required Duration for Secondary Water Supply?

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