Foam/Water Deluge System with Less Than K5.6?

3/23/2020

I have an existing foam/water deluge system covering vessels and sprinklers providing area coverage for pool fires. The sprinklers are smaller than K-5.6. The owner wants us to match the existing sprinklers.

In your opinion, is this acceptable?

For reference, NFPA 13 (2013) Section 8.3.4:
8.3.4 Sprinklers with K-Factors Less than K-5.6 (80).
8.3.4.1 Sprinklers shall have a minimum nominal K-factor of 5.6 (80) unless otherwise permitted by 8.3.4...
8.3.4.2 For light hazard occupancies not requiring as much water as is discharged by a sprinkler with a nominal K-factor of K-5.6 (80) operating at 7 psi (0.5 bar), sprinklers having a smaller orifice shall be permitted, subject to the following restrictions:
(1) The system shall be hydraulically calculated.
(2) Sprinklers with nominal K-factors of less than K-5.6 (80) shall be installed only in wet pipe sprinkler systems or in
accordance with the limitations of 8.3.4.3 or 8.3.4.4.
(3) A listed strainer shall be provided on the supply side of sprinklers with nominal K-factors of less than K-2.8 (40).
8.3.4.3 Sprinklers with nominal K-factors of less than K-5.6 (80) shall be permitted to be installed in conformance with 11.3.2 for protection against exposure fires.
8.3.4.4 Sprinklers with nominal K-factors of K-4.2 (57) shall be permitted to be installed on dry pipe and preaction systems protecting light hazard occupancies where piping is corrosion resistant or internally galvanized.

NFPA 15 (2017) Section 7.3.3. Flammable and Combustible Liquid Pool Fires
Water spray systems designed to control pool fires resulting from a flammable or combustible liquid spill fire shall be designed to apply a net rate of not less than 0.30 gpm/sqft of protected area.

I think my new design will require nozzles spaced at 100 square feet if the k-factor needs to be smaller than k-5.6 under NFPA 13.

Also, do you know of any non-aspirating nozzles that are listed for foam?

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4 Comments

RyanO link

3/23/2020 10:31:24 am

What are you adding protection to, specifically (area deluge w/ SSU, spray protection using directional nozzles, etc)?

Dan Wilder

3/23/2020 10:48:03 am

You need to confirm that the sprinkler is listed with the existing foam. If it is, then matching existing for change out should not be an issue.

If you are adding to the system I would think your foam supply may take a hit and you would need to adjust accordingly.

Ryan Hinson

3/23/2020 11:21:38 am

What were the applicable standards used for the initial design? NFPA 11 governs foam systems and NFPA 16 governs foam-water spray systems. NFPA 16 requires adherence to NFPA 15 unless otherwise specified. NFPA 16 does not require strainers in upstream FW piping. NFPA 15 (2017) does...under certain conditions:
- if the free-passage through the discharge is less than 3/8" per Section 6.4.6.1
- where the water is likely to contain obstructive material per Section 6.4.6.1
- intrinsic strainers at the nozzles are required if the free-passage is less than 3/16" per Section 6.4.6.3 (it must be noted that many petrochemical entities outright do not allow these types of nozzles since they are prone to plugging)
- Where strainers are required above, they must be able to remove solids of sufficient size to plug nozzles(normally, 1/8" is sufficient but must be verified where small K-factor nozzles are being used)

Is there already a strainer in the upstream piping? Does replacement of existing components with like K-factor nozzles require the addition of a strainer that was not there before?

Keep in mind that the hydraulics of a foam-water deluge system must be balanced to between 100% and a maximum 120% variation from specified discharge rate of the nozzle in accordance with NFPA 16 (2019) Section 7.10.1.1.1.

A standard sprinkler is an example of a non-aspirating nozzle per NFPA 16 Section 6.2.2. NFPA 11 (2016) Section 3.3.3.3 defines a non-air-aspirating discharge device as a device designed to provide a specific water discharge pattern...like a sprinkler. These are explicitly allowed to be used with foam deluge systems and are actually REQUIRED on wet-, dry pipe-, and preaction systems per NFPA 16 Section 6.2.3.

While the manufacturers I have discussed listings with have indicated that foam use in their nozzles does not affect the individual UL/FM listing/approval of the sprinkler, individual listings are not enough and the foam has very specific listing requirements and limitations regarding the 'listed system' per NFPA 16 Section 6.2.1 which includes discharge devices and proportioning equipment. This may include specific application densities dependent upon the specific hazard. I have found that many foam manufacturers also manufacture sprinklers/nozzles and may only list their foam with their nozzles. Consultation with both the foam- and discharge device manufacturers is highly recommended. Per one of the manufacturer's Listing and Approvals data sheet, refer to the UL listing guide or FM approval guide for the most current listing information as well as historic product listings.

Good luck.

Mike

3/23/2020 12:44:22 pm

NFPA® 16

Standard for
the Installation of
Foam-Water Sprinkler and
Foam-Water Spray Systems

Foam/Water Deluge System with Less Than K5.6?

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