Calculate In-Racks Without Changing Overhead?

5/3/2023

I have an existing warehouse that has a overhead pipe scheduled system from the early 80's. It is all threaded schedule 40 pipe. The system schedules from 8" at the riser to 2" at the last piece off main.

I ran a calculation and this existing system and it equates to Ordinary Hazard Group 2 at 0.20 gpm / 1,500 sqft.

The owner has installed (4) racks sections (per plan), each one separated by 12-ft. All located in one portion of the warehouse.

The fire marshal requested that they submit for a permit to confirm that the existing sprinkler system is adequate. The storage is 25-ft. (5-ft above the top of the 20-ft rack.) The ceiling is 35-ft.

The commodity is Encapsulated Group A, nonexpanded plastics on wood pallets, on open shelves with a 6" flue.

Plan view of storage configuration

Does NFPA 13, 2019 edition, section 25.8, option 1, 2 or 3 allow me to install sprinklers only in these racks, as a stand alone design, without making modification to the overhead sprinkler system?

This may eliminate the need for the owner to upgrade the existing overhead system and install a fire pump.

Thanks in advance.

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4 Comments

Josh

5/3/2023 08:08:40 am

I'm not sure what's up with this. 25.8.1.1 says it doesn't have to be hydraulically balanced with the ceiling. That would be my persuasion campaign topic with AHJ.

james evans

5/3/2023 11:59:49 am

This question has nothing to do with balancing the in racks with the system above. the question is this: can the above system be left at an ordinary group 2 occupancy even with in-racks and 25 feet of storage.

Group A plastics is a high risk storage arrangement and even with in-racks requires more than .20 over 1500. You would need to reference the code in CMDA sprinklers to get the area and density required for this storage arrangement.

Pete H

5/3/2023 02:24:23 pm

I'd say no.

You got over 20' of storage of group A plastics that you're protecting as OH2.

25.8.1.1. starts out saying where the commodities are protected in accordance with the guidelines of the section. And even then all 25.8.1.1 allows you is to not be required to be hydraulically balanced with the ceiling level sprinkler system. Yes, you could run a calculation on the in-rack only heads and have something that might be sufficient to that section, heck you could even take a chance that an AHJ will see your section notes and only wish to look at the in-rack calcs and system without expecting or requiring you to prove the existing system.... but that doesn't change that your ceiling system is not sufficient for your hazard.

(All opinion, take with a grain of salt).

Franck

5/3/2023 05:01:16 pm

Please note that 25.8.1.10 indicates that the ceiling sprinkler density shall be designed based on the highest commodity hazard not protected by the in-rack sprinkler system.

There is no storage configuration with rack or on pile that can be protected on a design for 1500 sq ft only. Minimum area of application for storage is 2000 sq ft.
This means that it is not certain that the remaining of your building is adequately protected either.

This chapter 25.8.1 was proposed to provide localized protection for higher hazard commodities, such as some racks with class IV commodity inside a storage area designed to protect goods classified as class II commodity.

For your information, FM Global made tests to evaluate the effect of mixing commodities in rack storage. Storage of 4 tiers with only one tier of group A plastic and 3 tiers of class II.
Tests were performed with plastic commodities stored at the bottom, at the top tier, or homogeneously mixed in the rack. For all tests, the results demonstrated that the protection needed to be designed for a plastic commodity.

So be careful if you want to apply this configuartion with plastic commodities, as already outlined by others above.
You will have to carefully install the horizontal (and potentially vertical) barriers. Otherwise it won't be effecient. Only option 1 is achievable in your case, as option 2 and 3 are using ESFR as in-racks (very high flow demand) .
In reality, it works, for a limited area, because it is like providing an intermediate protection that will prevent the fire to spread higher than 2 tiers and be controlled by the in-racks - the ceiling density is there only to protect the remaining areas).
It would be like having a protection for the storage below the first row of in-rack, then an independent protection for the storage between the first row and second row of in-racks, and then the ceiling protection for the top tier. This is why you don't need to balance the system.

Calculate In-Racks Without Changing Overhead?

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