Why FM ESFR & Shelf/Bin Box, but not NFPA 13?

2/18/2022

NFPA 13 does not allow ESFR protection for shelf or bin box storage. I can see the logic, and this has been in the code for years.

However, FM Data Sheet 8-9 does allow ESFR protection for shelf and bin box. I can protect shelving up to 15-feet with 0.85 over 2,500 sqft but I can't protect it with K25 at 70 psi.

Any insights on the logic here? Has testing been done that supports this one way or another?

Thanks in advance.

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3 Comments

Dan Wilder

2/18/2022 08:57:20 am

My opinion...there are likely some op-ed's or research papers to this issue but I'll see if those with more storage experience can populate those.

You're comparing a Control Mode density with a Early Suppression design criteria...there are two different end goals for these approaches and there is likely not enough supporting evidence to allow NFPA to let this section of the standard allow this configuration in the Suppression aspect.

FM vs NFPA are also different entities, FM typically involving several additional requirements to allow this configuration that likely go beyond just the blanket allowance for this protection scheme (spacing & obstructions, building construction/protection components, water supply & safety factors). They also can change their responsibility ($ on liability & coverages) based on compliance with all or some of their rules.

Just a couple of thoughts on this "finally" Friday! Have a good weekend all!

Jesse

2/18/2022 10:19:52 am

Happy Friday y'all.

I agree with Dan here. Seems you're comparing a Control-Mode criteria with a Suppression-Mode criteria. The pretense of these systems and design approaches are different. That 0.85 / 2,500 isn't a Suppression-Mode (ESFR) criteria but rather Control Mode.

NFPA never allows Suppression-Mode (ESFR) with any form of solid shelving. A lot of our design criteria seen in 13 is derived from test data, but not every scenario is tested. Considerable amounts of design criteria are extrapolated from other tests involving differing storage arrays and commodities, and then we use engineering judgment and modeling as a predictor. I once was under the belief that every design curve point and scenario was the result of testing but was summarily corrected of that assumption during an SFPE seminar and then NFPA committee meetings several years back.

FM is primarily for underwriting. Sometimes it can be more stringent than 13, and sometimes it just fills in gaps that are outside the scope of 13. But the way the standards are developed are very different.

And insurance loss control guys sometimes use the phrase "adequate for underwriting" which is entirely different can of worms.

Franck

2/18/2022 12:06:06 pm

In the good old time, FM Global (know at that time as Factory Mutual), was using density/area values in data sheet 8.9 (as well as other data sheet in the storage section), and had other tables for CMSA (designated at that time as Large Drop... nostalgia, nostalgia... and for ESFR.

A few years ago (2010), the Suppression Mode, Control Mode Specific Application and Control Mode Density Area sprinklers have been replaced with the term “Storage sprinkler” in the FM data sheet.
All ceiling-level sprinkler protection options are based on a single design format (i.e., number of sprinklers @ minimum operating pressure).
Reading an FM data sheet standards nowadays, for those who are used to NFPA is quite confusing.

Everything is in the same table, but it is difficult to see whether it is an ESFR design, or an "old" density/area design requirement with large orifice or extra large orifice sprinklers. You can guess that a K25 is probably an ESFR, but for some K-factors, it is difficult to say whether it is spray sprinkler, CMSA sprinkler or even ESFR.

Roughly, what they are doing for the "old" density/area design is :
- convert an area in a number of operating sprinklers (1500 sq ft is 15 sprinklers, 2500 sq ft is 25 sprinklers...), assuming that the average maximum area covered for storage aoccupancies is 100 sq ft.
- convert a density (gpm/sq ft) into a pressure demand (psi) based on the K-factor and assuming again a 100 sq ft per sprinkler.

To be honnest, I strongly suggest you to follow NFPA 13 requirements. And if you really need to follow FM requirements for storage, better ask an FM engineer to avoid any misinterpretation.

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Why FM ESFR & Shelf/Bin Box, but not NFPA 13?

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