Why Multiple Storage/Roof Options Listed in 13?

10/21/2022

In the 2016 edition of the NFPA 13, Table 13.2.1 in the part of "Group A Plastic Storage", in the paragraph of "Exposed", there is an option of "Expanded" and an option of "Unexpanded and Expanded".

Link: https://link.nfpa.org/free-access/publications/13/2016

There are two storage arrangements that end up with OH2 with +1 Level of In-Rack (all other criteria are the same):

Expanded, 5-10 feet of storage, up to 20-ft ceiling/roof height
Unexpanded and Expanded, 10-12 feet of storage, up to 32-ft ceiling/roof height

It seems that the second option will always be better than the first option in reference to the permitted storage height.

Why have the maximum 10 feet storage option if you can always go for the maximum 12 feet storage option?

(Even for a building that is lower than 20 feet, you can go according to the option of storage of 12 feet in a building that is up to 32 feet)

Thanks in advance.

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13 Comments

Dan Wilder

10/21/2022 08:25:38 am

Looking into the handbook commentary, the only conclusion I can come up with is the ability to use QR reduction but in using that smaller HMRA, the storage height is limited to 10' (in a 20' building) vs the ability to utilize the full 12' for Misc Storage (for buildings up to 32'). It also plays into the use of HMRA increases for sloped ceilings.

Both the increase and decrease allowance/requirements are specific to Chapter 13 only for misc. storage.

Jesse

10/21/2022 08:42:22 am

In the EXPANDED row, all commodity in that storage array is expanded Group A.

In UNEXPANDED and EXPANDED, there is a mix of expanded and unexpanded Group A plastic commodities.

10/21/2022 08:53:22 am

Since I don't get into this near as much as I would like to..

Are you using the classifications defined in 5.6.4.1 (and the subsequent charts 5.6.3.3.3(a) & 5.6.3.3.3(b) for that determination?

10/21/2022 08:43:56 am

So if your storage array ONLY includes expanded Group A plastic products, you have to use the >5 to <10 design criteria.

If you have a mix of expanded and unexpanded, you can go 10-12 ft.

Franck

10/21/2022 12:16:14 pm

Jesse, that's not correct.
Expanded and unexpanded means that this applies both to expanded and unexpanded. Not a mix of, but could be 100% expanded or 100% unexpanded.
Normally expanded is by far the most demanding.
But remeber that section 13 only apply to miscelaneous storage. To be handled very carefully with plastic storage.

Eric R

10/21/2022 10:10:58 am

Jesse, I don't believe you are correct. This chart doesn't make any determinations on mixing of commodities.

The chart layout is based first on whether the commodity is cartoned or exposed. The second organizational factor is actually storage height even though this isn't displayed until the 4th column.

How it works is that for under 5' height you can store both expanded and non expanded plastics in any storage arrangement using OH2.

Then, going above 5' of storage up to 10' of storage the chart starts to list separate design requirements based on being expanded or unexpanded, and then on what storage arrangement is being used.

So for 5' to 8' you can do palletized/shelf/solid/etc and have a roof height up to 28' and be ok with EH2. BUT if that storage is on racks then to keep it in EH2 you need to keep storage to 10' max and only get a ceiling height max of 15'. This again is for both kinds of commodity.

Then the next two chart lines take that same 10' max storage height and delineate between expanded from non-expanded. So for this section you can bump your ceiling height up from 15' to 20' but only for non-expanded commodities and still be at EH2, BUT to get your ceiling height up to 20' for expanded commodities you're going to have to use in-rack sprinklers!

Finally getting to the original question. The final three lines of the chart pretty much start the whole process over again for storage heights above 10' and up to 12'. So the questioner is correct that for expanded rack storage there is no difference between 5'-10' and 10'-12'.

However, the reason this last section of the chart exists is for UNEXPANDED plastics. If you want rack storage for EUP and are 10' or less in height you can protect it with ceiling only sprinklers at EH2, BUT if you jump up to 10'-12' then you are REQUIRED to use in-racks sprinklers, but conversely the ceiling drops down to OH2. So this could be a very big cost change for that extra 2' of rack storage of unexpanded plastics.

Final Note:
Don't forget that all of these storage arrangements regarding plastics are for Miscellaneous storage ONLY. If the storage area doesn't meet the area and stack size limitations for that designation, and is a plastic commodity over 5' height you can't use chapter 13 at all!

Hope this helps!

10/21/2022 12:12:56 pm

That's the perfect answer !
Very clear :)

Zecharya

10/22/2022 11:48:54 am

Thanks Eric for your detailed answer!

You say there is a redundancy in the table, as there is a lot in the ESFR tables. I agree.

I want to ask about the table of miscellaneous, is it also relevant for low pile storage option?

10/22/2022 12:11:52 pm

Only for Class 1-4 commodities. If the commodity is classified as a group A plastic then this table can’t be used unless the storage area is small enough to be considered miscellaneous storage.

This distinction is a bit more clear in the 2019-2021 editions of NFPA 13 but IMO could still use some more refining.

Low piled plastics storage should probably be it’s own section if for no other reason than that self storage facilities are an increasingly common and it drives me batty to see specs classifying the hazard as OH2 because the storage height is less than 10’.

10/22/2022 11:31:42 pm

Eric,
I thought the only difference in the 2016 edition between millennius and low pile is solid shelving, like it says in the Handbook.
the table is titled only for miscellaneous so how come you say commodity class 1-4 is part of the table and plastic A isn't?
Thanks

I agree that the 2019 and 2022 address the to subjects in different paragraphs, that's why I'm asking only on the 2016 edition...

10/23/2022 12:04:00 pm

13.1.1 is where this is delineated.

-This chapter shall apply to any of the following situations:
(1) Miscellaneous storage of Class I through Class IV commodities up to 12 ft (3.7 m) in height
(2) Miscellaneous storage of Group A plastics up to 12 ft (3.7 m) in height
(3) Miscellaneous storage of rubber tires up to 12 ft (3.7 m) in height
(4) Miscellaneous storage of rolled paper up to 12 ft (3.7 m) in height
(5) Storage of Class I through Class IV commodities up to 12 ft (3.7 m) in height as directed by 14.2.3.1 and 16.2.1.2.1
(6) Storage of Group A plastics up to 5 ft (1.5 m) in height as directed by 15.2.1 and 17.2.1.1

Rules 1-4 apply to 12' of storage of all the main commodity types as long as the storage area can be considered miscellaneous. Then rules 5 and 6 explain that the chart can also be used for general storage, but only if allowed by the specific sections in chapters 14, 15, 16, and 17.

Chapters 14 and 16 reference this table for storage heights up to 12' of Class I-IV commodities, but chapters 15 and 17 only reference this chart for storage heights up to 5' of Group A Plastics.

You are correct that Chapter 13 gives additional requirements for solid0shelf racks due to the lower ceiling sprinkler densities provided by the chart which may not be adequate for larger/denser storage arrangements even with the low max height.

10/23/2022 12:12:50 pm

You are absolutely correct!
I did not realize that difference in the different subsection.
Thanks!

10/23/2022 12:22:06 pm

https://www.youtube.com/watch?v=xHiAl-TnqCY

Here is a great video by FM Global that makes it very clear how dangerous plastics storage can be. This burn test is for exposed unexpanded plastics at 6' with Extra Hazard 1 protection provided.

With the table we've been discussing here, you could technically protect this commodity at 5' storage height with OH2 and not be limited by the miscellaneous storage rules. But after watching that video do you think 1' less of pallets would suddenly be controlled by 2/3rd as much discharge?

This is why as soon as you get past 5' of storage for plastics you have to stay in the main plastics storage chapters.

Why Multiple Storage/Roof Options Listed in 13?

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