IBC Sprinkler Height

[FPE22]

Hello,

I know this is an NFPA forum, but maybe some of you have the expertise in IBC as well.

IBC 2015 mentions in Section 404.3 that sprinklers are not required where the ceiling of atrium is above 55 ft height. In the "IBC Code and Commentary" they explain that sprinkler systems are no longer effective at 55 ft and that installing them provides little benefits.

Does anyone know what they’re basing this explanation on? Is there any paper/criteria that allow us to know whether sprinklers are effective or not if they’re on a certain height? If performance based design is the answer, what criteria should be considered in making our study?

Thanks for your help.

 

[cdafd]

Cannot answer your question, but has been in IBC since the 2003 edition

 

[stookeyfpe]

The assumption is based on IBC Section 909.9. One wants the smallest design fire as possible so as to limit the size of the air handling equipment. Atrium designs are sensitive to the size of the fuel package and generally speaking, the design fire assumptions place limits on what the owner is allowed. Secondly, neither the engineer nor owner want to introduce a fuel load that is so great in a 60 foot tall atrium that the smoke cannot be cooled by the volume.

As to the basis of the 55 foot number, I seem to remember it was based on a literature search of European FP Engineering research, but I'm getting older so my answer is questionable.

 

[Sdpaddler50]

FM did some full scale fire burn test about 10 years ago. The sprinklers don't get the heat they need to operate at these high ceiling heights.

 

[NightME]

In tall areas, like atria, the smoke will stratify somewhere between the floor and ceiling based on smoke layer temperature and ambient temperature. Since the smoke will stratify we don't have smoke detectors at the ceiling, we generally look for beam detection at some calculated height.

This same concept applies for the heat movement towards the ceiling. As the heat rises it will cool, the amount it cools is based on the fire heat release rate, fire area, and ambient temperature. With tall spaces this cooling effect becomes more significant and generally results in sprinklers not activating...it's hard to hold 165F at the sprinkler location for sufficient time to operate because of this cooling effect. I've discussed with AHJs the omission of ceiling sprinklers in these situations and the addition of added detection or notification, it's usually met with positive results.

As mentioned previously, FM has performed testing and agree that sprinklers aren't nearly as effective in opening at these heights. You can also consult NFPA 92 for some discussion on heat layers and calculation methods.