Why Did FM Data Sheet 8-1, Table 1 Change?

8/3/2026

Does anyone know any background on the changes to Factory Mutual Data Sheet 8-9, Table 1?

The table used to use a set of formulas for all designs, which would apply a shape factor of 1.2 or 1.4 depending on ceiling construction/slope. It appears to have been updated in July of 2025, with changes being brought in that would allow 12 sprinkler designs to be calculated on the basis of 3 heads on 4 branch lines rather than using the old formulas, which, based on minimum spacing, was not possible for this to occur.

There are no comments in the back or anything on FM’s website linked to testing that supports that change; any help would be appreciated.

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4 Comments

anthony

8/3/2026 07:47:20 am

FM has more designs than 12 sprinkler ESFR 3x4 arrangements so this allows for more specificity for those design criteria.

Table 2 alone shown dry systems operating 25 sprinkler for dry systems.

My guess is a few folks got creative and found ways of interpreting the directions incorrectly to make the install easier.

Anon

8/6/2026 06:26:28 am

Thanks for the comment Anthony.

I was more talking about the specifics of shape factors for hydraulic calculations referenced in table 1, not if there are different design for given commodity or ceiling height.

Prior to 2025 a 12 sprinkler design was calculated as 3 ranges each with 4 heads in operation based on the use of Equation 1, as per the below.

(1.2/SAVG)x([NumberofSprinklersinCeilingDesignxSAVG xLAVG ])0.5

The above formula could mathematically not produce a design of less than 4 heads per range.

(Table 1) now just says if ceiling slope is less than 5 degrees, and sprinklers are spaced further than 2.7m apart, you don’t need to use the formula, you just calculate 3 per branch line.

This has a significant impact on loses in branch lines, as the velocity is massively reduced, for example, k25 @ 4.1 Bar, would mean rough figures, your getting 2200 L/min down each branch, rather than 2940 L/min.

I’m just curious, as to how this has been updated as a minor change, when it appear pretty significant in terms of design impact.

Jose Figueroa

8/3/2026 10:27:24 pm

We recommend subscribing to the FM Data Sheets, which are available at no cost unlike some other standards. They often send helpful updates via email about the Data Sheets, and you can easily reach out to them with any questions or more. It's a great way to stay informed and connected.

Anon

8/6/2026 06:28:29 am

Thanks Jose,

I’m and member, but wasn’t aware there was An avenue to reach out and speak direct to them, thanks for the help.

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Why Did FM Data Sheet 8-1, Table 1 Change?

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