Sprinkler Protection for Large Atriums

[keenfirengineer]

Hi,

I'm currently designing a dome atrium with a diameter of 100m and the height ranging from 8m up to 24m.
The highest point being at the center of the dome.
The space below is used as circulation space and pop up kiosk.

Based on British Standards, the height limitation for sprinkler provision is up to 17m.
I have referred to NFPA 13 and it does not state any limitation on the height of sprinkler installation.
Thought of using ESFR but there are height limitations prescribed in NFPA, up to 45ft.

Referred to FM 3-26 (Sprinkler for Non-Storage Occupancies) 2014 and found that FM had prescribed the requirement up to 30m that sprinklers are to be provided based K-Factor and stated minimum supply pressure.
Then found out that in FM 3-26 2019, FM had completely revised the data sheet and now sprinkler provisions up to 30m are based on design density and area of coverage. It states a design density of 0.6gpm/ft2 in an area of 1200 sqft. Never seen a requirement of 0.6gpm/ft2 and already guessing that the flow rate is going to be incredibly high.

Next, tried looking for sprinklers that have approvals with K-factors of 25.2 and noticed that all I could find are ESFR sprinklers.

So back to square one.

Any suggestion on references or sprinklers that would be able to serve such heights?
Anyone knows of any similar buildings and its provisions?

Note: Deluge systems were considered but due to the openness of the space, a double knock system would not be practical as there will be overlapping of zone activation. Plus, the tank size would be incredibly large.

 

[TravisMack]

There are K25.2 sprinklers that are NOT ESFR. Tyco EC-25 is one. Reliable makes one. I believe Viking does as well. Victaulic has the LP-46, but it is a CMSA sprinkler.

Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, a Ferguson Enterprise

http://www.mfpdesign.com

 

[UFT12]

0.6 gpm/ft2 over 1200 ft2 is not an incredibly high supply. That's 720 gpm, less than EH1 (0.3 gpm/ft2 over 2500 ft2) per NFPA 13. Your branch lines may come a bit larger than usual but nothing extraordinary really. As to why should you consider EH instead of OH (which I will assume you would expect for your building) it's because the height of the dome will allow for a larger fire evolving before the first sprinkler activates. So it make sense to expect a higher amount of water.

A K factor of 11.2 (SI 160) would give a pressure of ((0.6 x 100)/11.2)^2 = 29 psi or 2 bar. Assuming that the average sprinkler coverage may be less than 100 ft2, say 90 ft2 the pressure may be come 23 psi or 1.6 bar which again nothing too fancy. Should you go for a K factor of 14 or SI 200 you may end up with a head pressure of 15 psi or 1 bar which depending on your design, it may be even better.

 

[keenfirengineer]

TravisMack,
Thanks for your input. I have reviewed EC-25 but it is an upright type. I would require a pendent type as the sprinklers would be installed below the steel structure supporting the dome and glass.
Victaulic's LP-46 is a pendent type and might just fit the application.

UFT12,
You're spot on, I've determined the hazard classification as OH2.
Thanks for your clarification.
Meaning if I use a K Factor of 25.2 and assuming sprinkler coverage of 100sqft, it will be (0.6x100)/25.2)^2 = 5.7 psi or 0.4 bar.
The pressure is relatively low.

However, I'm facing an issue with the local fire authority in which they have asked me to refer only to NFPA as the overall building standards is to NFPA and they do not allow us to carve the dome atrium out and applying FM as the design standard.
Can't find any reference within NFPA to justify the use of sprinklers with higher K-factors for higher ceiling heights.
Still finding a clause that I could use to substantiate using a higher K-factor for higher ceiling height.

 

[cdafd]

Can't find any reference within NFPA to justify the use of sprinklers with higher K-factors for higher ceiling heights.
Still finding a clause that I could use to substantiate using a higher K-factor for higher ceiling height.


Design outside the scope of 13,,, May I use another design standard

 

[UFT12]

There isn't any reference in NFPA 13 in regards to such high ceilings for the discharge criteria or K factors. I once had the chance to meet with Mat Klaus and Bob Caputo (both members of the NFPA 13 committee) and personally asked precisely about that matter. They replied that there is nothing in the standard to mandate special measures. Simply put, apart from storage occupies, ceiling heights are still not addressed by NFPA 13.

@keenfirengineer, just do what NFPA 13 mandates per OH2 or state that in lack of info in NFPA 13, FM for the dome was used and let the authority decide. Also, a K 25 would make you increase the discharge higher than 0.6 gpm/ft2. Observe the minimum head pressure requirement in chapter 27 (7 psi/0.5 bar).