Lower ESFR Sprinklers Below New Obstructions?

12/1/2023

We're working on a building that is an old 2-story storage steel building that was fitted with an ill-installed K14 ESFR system. It neglected roof construction, obstructions, and distance from the roof some 20-years ago.

A new owner has removed floor separations, understands that the sprinkler installation must be renewed, but has based the renewal on the possibility of continuing the use of ESFR here.

Due to the roof construction in two large (open but not connected) building sections with about 500 sprinklers each, there are some problems for 5-10% of the sprinklers in these areas. Half of them will have problems with obstructions or distance from the roof and will be "doubled-up" less than 2-ft from a dividing baffle.

For the other half there may be a solution based on lowering these (shown below); light gray are trusses with a slight riser at the upper belt. Green is a part of the horizontal wind bracing crossing H-beams. Red are sprinkler pipes.

The lowered ESFR K25 will have the mid-point of the glass bulb within the maximum allowed distance from the roof (that have a maximum height of 34-ft from the floor).

Is this an acceptable solution for a small number of sprinklers (one here, one there) in a larger section?

Is there an issue with some of the sprinklers being at the lower limit, while others are higher in elevation?

We can't get rid of the wind bracing, so will the water demand still be based on 12 activated sprinklers even if they're closer together?

Thanks in advance.

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6 Comments

Glenn Berger

12/1/2023 08:14:36 am

The statement "one here, one there" is a red-flag for me. I would be okay with deflectors at differing elevations as long as they are still in compliance with positioning in accordance with NFPA 13.

Jesse

12/1/2023 08:44:56 am

Agree with Glenn on the concerns regarding "one here, one there".

The differing heights are ok as long as the deflector is the maximum distance from the deck, not the bulb.

Dan Wilder

12/1/2023 08:47:42 am

A lot to digest...

Existing 2 story building with the 2nd floor being demo'd creating a 1 story with taller storage capacity & clear height for storage system with existing k14 ESFR
-System being converted to use K25's
--Assumption being the K25's are allowed for the storage method criteria below

Locations of existing sprinklers are obstructed.
-Using a mech tee/drop is being proposed to avoid the roof deck level obstructions
--Compliance with 13-19 14.2.10.1.3 using 6"-18" deflector distance...the statement of the glass bulb centerline is of no use in this scenario, it must be from the deflector and no, there is no issue with one deflector being at the minimum and another at the maximum, they both comply.

Sprinklers are closer than 8'
-Using baffles as needed
--There have been several NFSA EOD's that have confirmed that ESFR spacing cannot be less than 8' regardless of baffles/structural obstructions or even walls (2' or greater) and that staggering the sprinklers in adjacent bays was the only acceptable solution

Month-Year / Tech Notes Question # & applicable NFPA 13 year
12-08 #5 13-2007
1-15 #2 13-2013
2-16 #7 13-2013
7-17 #7 13-2016
3-18 #11 13-2016

Now in 13-2022 Sections 14.2.4.3 for obstructed construction (not applicable in this case of open web trusses) & 14.2.9.4.1 for buildings with unobstructed construction & 14.2.9.4.2 when baffles are utilized has 5 criteria that now allows spacing closer than 8' based on FM reporting for K25's that showed it was acceptable.

1-Baffles complying with 14.2.11.1.1
2-Baffles shall be solid and rigid material
3-not less than 8" long & 6" high
4-Top of baffle shall extend 2"-3" above the deflectors of uprights (not your case but for clarity)
5-Bottom of baffle shall extend downward to at least level with the deflectors of pendent sprinklers

The design area of 12 sprinklers per 23.2.2 is still correct however, the minimum remote area size of 768 FT² may still be requested/required per 24.1.8.2.

Franck

12/1/2023 03:42:17 pm

From a practical point of view, I would suggest to make the analysis on the final configuration.

It is not the same if the roof is at 20 ft or 35 ft.
It is not the same if you have a 20 ft high storage or a 30 ft high storage.
It is not the same if this is drr with at least 8 ft aisles or mrr.
And it is not the same if it is a class III commodity or an exposed Gr A plastic.

If you have class III with drr up to 20 ft, I won’t be too afraid. If you have 30 ft high mrr with group A plastic, any small “deviation” from the standard becomes a huge issue.
K14 that were allowed in some previous configurations are not anymore permitted with the latest nfpa 13 editions.

Maybe it could be good to make an hydraulic calculation with 14 ESFR (12 + 2 as for obstructed constructions and sprinklers underneath).

This being said, I am normally quite confident with ESFR protection (if no slope, no under-estimated obstruction, and no fan with high velocity at ceiling level) as experience shows that (almost all) fires are generally extinguished with less than 4 sprinklers.
The 12 sprinklers design is a margin taken when you involve the second rows of sprinklers (if fire spread in all directions the same way, first row is 4 sprinklers, and second row is 8 additional sprinklers)
Easier to understand with a drawing

——————X———-X——————--

-——X———X———-X———X——--
Fire start.
——-X———X——-—X———X——--

——————X——-—X——————--

But this is not based on standards, just on some common sense and sense of judgement that is always necessary to analyse an existing situation to determine if this is acceptable (when it can’t be satisfactory)

12/1/2023 03:46:04 pm

On the above “drawing”, the fire starts in the center of the 4 sprinklers (most adverse location) and then spreads in all directions to open the 8 sprinklers on the second rows (2 on top, 2 at left side, 2 at bottom and 2 at right side)

sean

12/31/2023 05:56:27 pm

any sprinkler within the range is acceptable.
note that typically it is measured from the defector not from the center point.

Lower ESFR Sprinklers Below New Obstructions?

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