Store Exposed Group A in Lowest Rack Only?

4/29/2024

Consider a high-piled rack storage area with 30 ft roof height and the following arrangements:

(A) Class I through IV and cartoned nonexpanded Group A plastic up to full rack height
(B) Exposed nonexpanded Group A plastics, only up to five feet

NFPA 13 Table 23.3.1 prescribes protection criteria for (A) as pendent K25.2 at 15 psi starting pressure; however, it does not provide protection criteria for exposed nonexpanded Group A plastics using K25.2 sprinklers where ceiling height is ≤ 30 ft. NFPA 13 Table 4.3.1.7.1.1 prescribes protection criteria for (B) as Ordinary Hazard Group 2.

The owner will have exposed nonexpanded Group A plastics. They have agreed in writing to maintain exposed nonexpanded Group A plastic to the bottom five feet of the racks.

Would storing exposed nonexpanded Group A plastics only in the lowest five feet of the rack, with Class I-IV above to the full rack height, be permissible?

If so, the overhead sprinkler design under NFPA 13-2022 § 20.4.13.2 would only require the more-demanding of the two criteria (which is A), correct?

Some have suggested that the presence of the exposed nonexpanded Group A plastic within the (A) criteria mixes with the (B) criteria to form a more hazardous condition than posed by either individual commodity / arrangement. However, NFPA 13 § 20.4.13.1 and 20.4.13.2 seem to require each commodity / arrangement to be considered independently and not to hypothesize protection requirements based on commodity / arrangement mixes.

Long one, but thanks in advance.

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10 Comments

Pete H

4/29/2024 07:03:25 am

Check out NFPA 13 (2022 edition) Table 4.3.1.7.1.1

Specifically check out Exposed Unexpanded plastics in rack protection on that chart.

If the top of the group a nonexpanded exposed storage is less than or equal to 5'-0" in elevation, that is equivalent to an OH2 design curve on Figure 19.2.3.1.1 (1500 square feet at 0.2 density).

Which is not going to be your final demand, as your esfr calculation is significantly more demanding and would prove out this requirement and your OH2 area is covered as per your 23.3.1 design as per 23.1.1(3).

CONCERNS: If you have solid shelf racks and this exceeds the requirements of "Miscellaneous Storage" and is in "Low-Piled Storage", in rack sprinkler protection is still required (4.3.1.7.2.6)

Glenn Berger

4/29/2024 08:08:43 am

Administrative control of storage arrangement / commodity is commonplace. Failure to comply with this approved administrative control is also commonplace.

4/29/2024 08:18:00 am

You cannot store a higher commodity below a lower commodity in racks without solid horizontal barriers. NFPA 13, 2016 §5.6.1.2 "Mixed Commodities" and §5.6.1.2.4 "Mixed Commodity Segregation" provide guidance on when you can and cannot mix commodities. Generally speaking, you can't mix commodities without using solid barriers and in-rack sprinklers. The handbook right below 5.6.1.2.4 specifically states that FM Global testing found that placing Group A plastics below class III commodities resulted in the need for Group A plastic protection.

There are alternate in-rack design schemes in NFPA 13, 2016 + 2019 + 2022 for segregating high hazard storage in specific areas of racks, otherwise the roof needs to be designed to protect the highest level of commodity being stored.

Franck

4/29/2024 09:17:24 am

As indicated by Glenn, it is nice to have rules, but most of the time, rules are not considered on the long term.

In addition to that, NK is right.

It is not fine to have group A plastic at the bottom and another commodity above and considering that the protection is fine at the ceiling because it is fine for both taken individually.
Because they are not stored individually.

The plastic commodity needs to be considered as a plastic commodity for the entire rack and the best you can do is to provide in-racks above this storage as indicated by NK.
Then you have 2 solutions:
1- to provide solid barriers above and you only need one level of in-racks.
2. Not to provide solid barriers and consider the entire rack as plastic (with the necessary requirements in term of in-racks and density at ceiling).

David Kalinec link

4/29/2024 09:18:56 am

Unfortunately, the proposed scenario is not compliant without horizontal barriers, in-rack sprinklers as mentioned in other replies, or some other engineered solution. Assuming this is under the 2021 International Fire Code, §3204 and §3206.3 prevent this arrangement. The way I explain it to my clients is to consider the plastics on bottom as the burner underneath their stovetop grate. The plastics turn the dial to high-heat instead of medium heat. It is added fuel that otherwise would not be there.

Streeter

4/29/2024 10:07:43 am

We have done some storage arrangements similar to this and have found that is this scenario, the use of ESFRs is almost always going to be a hydraulically less demanding system than an OH2 system.
Going through the tables mentioned above will give you a more direct answer but only having to calculate the 12 most demanding heads is often a lot better hydraulics wise than 1500SF of OH2.
The layout is a bit more involved due to the 8’-10’ min/max spacing requirements, and the requirements for obstructions, and the soon to be added requirements for distance of heads from ceiling to added in 2025.

Jon

4/29/2024 01:22:17 pm

Glenn's comments are spot on. As a former AHJ with 37 years of experience as a fire marshal, I have rarely seen compliance with "promises". "I promise not to let more than 49 people into my business with one exit - until I have a sale." "I promise not to store more than 12 feet high so it is not high-piled storage - until I figure out that I have a large volume of space that I could use." "I promise not to use my large assembly venue for concerts - until I find that I can make a lot of money even though I chose not to sprinkler it."

Go to almost any big-box retail store and you will see in-aisle or end-cap displays that were never contemplated in the sprinkler design. Unless there is a way to ensure compliance with the "promise", I was not interested in it. We had a facility put up chain link and chicken wire fence above the level of adequate sprinkler protection to avoid in-racks so that the forklift operators couldn't stack materials to the roof deck.

I never considered myself to be an unreasonable fire marshal and was often told that I was reasonable to deal with. Experience has shown me that Murphy's Law can happen (and often does with fire). As a fire marshal in the neighboring town used to say: "Why don't people just design in compliance with the code rather than trying to design around it?".

Brandon Wilkerson

4/29/2024 01:59:05 pm

To those stating that this is not allowed because higher hazard commodities cannot be stored within a rack without designing to the high hazard commodity, regardless of the storage arrangement:

I submit for your consideration NFPA 13 (2022) 20.4.13.2 which states "Unless the requirements of 20.4.13.3 or 20.4.13.4 are met, mixed commodity storage shall be protected by the requirements for the highest classified commodity AND storage arrangement."

Emphasis on "highest classified commodity AND storage arrangement."

In my opinion, 5 feet of exposed nonexpanded Group A plastic is a LOWER hazard commodity/arrangement than ~30 ft of cartoned nonexpanded Group A plastic. As evidence, I submit the low-piled storage criteria in § 4.3.1.7.2 which defines 5 ft of exposed nonexpanded Group A as OH2. If this is true, then the sprinkler system must only be designed to protect the higher hazard commodity/arrangement (in this case, clearly the ESFR system).

Further, NFPA 13 (2022) § 20.4.13.1 explicitly states that design must not be based on the overall commodity mix.

So, just from an NFPA 13 perspective, it seems that one must compare all of the various commodities *at their planned arrangement*, and design to the most restrictive. Struggling to find NFPA 13 rules which dictate otherwise.

Great discussion, thank you all!

4/30/2024 08:11:04 am

"highest classified commodity AND storage arrangement" refers to the most demanding commodity and the most demanding arrangement. For example, if you have class IV commodities and cartoned expanded group a plastics in a rack then you would protect the rack for the cartoned expanded group a plastics since it is more demanding. Like wise, if you have a warehouse with single-row racks and multiple-row racks you would protect the warehouse for multiple-row racks since it is more demanding.

Pete D.

4/30/2024 08:27:10 pm

This kind of goes along with what others were saying regarding mixes commodities and rack barriers. When you get into NFPA 13 sections /tables on ceiling-only protection of group A plastics in racks, it gives a 0.6 density, but it also comes with a 10 ft maximum clearance between the storage and roof. That is if youre storing 15 ft in a 30 ft building, you must protect as though you're atoeing at 20 ft. This is echoed in the General Storage requirements (used to be Ch. 12), and it's all throughout FM's design criteria, NFPA 13 tire storage, etc. I've installed a single line of in-rack sprinklers with a horizontal barrier in the past to protect class III combustible liquid IBCs in the lowest tier. Think of the horizontal barrier as a way of bringing the ceiling to the storage instead of vice versa.

Store Exposed Group A in Lowest Rack Only?

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