when can a ceiling be considered "open-grid" 1

[acb324]

I was unable to find an NFPA definition of open-grid ceiling, do any of you know if this exists? To me a grid implies lines running in both directions. Typically an open-grid ceiling looks something akin to a 2'x2' acoustical tile ceiling before the tile gets put in.

I am the engineer designing the sprinkler system for a building which has what were originally described to me as "louvered" ceilings. Basically there are 2" wide baffles that run only in one direction. There is 10" of space between (so the 2" pieces are installed 12" on center). These baffles are 8" deep vertically. As I see it I have a ton of continuous obstructions running throughout the entire level. The above ceiling volume is huge and not concealed, so I called for sprinklers both above and below the ceiling. I am being challenged that because the open area is greater than 70% and the 8" depth doesn't exceed the 10" spaces, they can consider this an open-grid ceiling. I don't think this should be the only consideration, and I still contend that a grid should mean, well... a grid!

The annex material of A.8.15.14 even states: The installation of open-grid egg crate, louver, or honeycomb ceilings beneath sprinklers restricts the sideways travel of the sprinkler discharge and can change the character of discharge.

Thoughts?

 

[cdafd]

There is a definition will have to find it for you

 

[cdafd]

From 06 will have to check to see if it is current

First page right side

http://www.tyco-fire.com/TFP_common/Stationhouse_111506.pdf

Would rather see a plan but does not sound like you have an open grid

 

[acb324]

Thanks cdafd! tell me - what makes you say it doesn't sound like an open grid?

The argument goes like this: NFPA 13 contains specific geometric criteria by which open grids can be placed below sprinklers.
[ul][li]Openings must be at least 1/4" wide in the least dimension - openings are ~10"[/li]
[li]and at least 70 percent open - 2" slats and 10" openings means approx. 83% open[/li]
[li]The depth of the ceiling panels is not permitted to exceed the least dimension of the grid openings - depth is 6-8" (I have heard both from architect) and it is less than the 10" openings[/li]
[/ul]

Technically I suppose it meets all the dimensions dictated in the document you provided (which is same as open-grid section of NFPA 13). I guess I was hoping for something that excludes louver type ceilings from the open-grid section, like a definition of open-grid. I mean from what I wrote above it might seem like I just made the case that it is an open-grid ceiling but I think that it is misleading. If there were a section on sprinklering grass - and the requirements for the grass listed in that section are that its green and leafy... that doesn't mean that lettuce is grass and covered by that standard, even though it is also green and leafy.

I also keep reverting back to A.8.15.14 which states: The installation of open-grid egg crate, louver, or honeycomb ceilings beneath sprinklers restricts the sideways travel of the sprinkler discharge and can change the character of discharge.

 

[cdafd]

ok now I see the picture, I think you do have so called open grid

I was thinking it would look different. What I have seen in the past that I considered open grid, is the egg crate looking tile

http://www.ceilingtiles.ie/ceiling-...cessories/eggcrate_thumb_11280320-500x500.gif

Your other problem if you do require heads below the ceiling, is will they even activate?? will they collect enough heat to fuse??? more then likely NOT.

Thanks for being pro fire protection





8.15.14* Open-Grid Ceilings. Open-grid ceilings shall only be installed beneath sprinklers where one of the following is met:


(1)
Open-grid ceilings in which the openings are ¼ in. (6.4 mm) or larger in the least dimension, where the thickness or depth of the material does not exceed the least dimension of the opening, and where such openings constitute 70 percent of the area of the ceiling material. The spacing of the sprinklers over the open-grid ceiling shall then comply with the following:


(a)
In light hazard occupancies where sprinkler spacing (either spray or old-style sprinklers) is less than 10 ft × 10 ft (3 m × 3 m), a minimum clearance of at least 18 in. (457 mm) shall be provided between the sprinkler deflectors and the upper surface of the open-grid ceiling. Where spacing is greater than 10 ft × 10 ft (3 m × 3 m) but less than 10 ft × 12 ft (3 m × 3.7 m), a clearance of at least 24 in. (610 mm) shall be provided from spray sprinklers and at least 36 in. (914 mm) from old-style sprinklers. Where spacing is greater than 10 ft × 12 ft (3 m × 3.7 m), a clearance of at least 48 in. (1219 mm) shall be provided.


(b)
In ordinary hazard occupancies, open-grid ceilings shall be permitted to be installed beneath spray sprinklers only. Where sprinkler spacing is less than 10 ft × 10 ft (3 m × 3 m), a minimum clearance of at least 24 in. (610 mm) shall be provided between the sprinkler deflectors and the upper surface of the open-grid ceiling. Where spacing is greater than 10 ft × 10 ft (3 m × 3 m), a clearance of at least 36 in. (914 mm) shall be provided.




(2)
Other types of open-grid ceilings shall be permitted to be installed beneath sprinklers where they are listed for such service and are installed in accordance with instructions contained in each package of ceiling material.



The requirements in 8.15.14 for clearance between the sprinkler deflectors and the top of the grid ceiling ensure that sprinkler discharge is not too severely impaired. The grid ceiling can obstruct the discharge pattern to some degree. In addition to the height above the grid ceiling, other obstructions, such as pipes or ducts, must also be considered.




A.8.15.14 The installation of open-grid egg crate, louver, or honeycomb ceilings beneath sprinklers restricts the sideways travel of the sprinkler discharge and can change the character of discharge.

 

[acb324]

Yeah, I thought about that and was calling for heat collectors on the lower layer of sprinklers. Thank you for you input!

 

[cdafd]

heat collectors would not fly in my ahj

they do not work for future reference



In the 2010 edition of NFPA 13, the technical committees that develop the design and installation standard have
included very clear language: “Heat collectors shall not be used as a means to assist the activation of a sprinkler.”

http://www.usfa.fema.gov/downloads/pdf/coffee-break/cb_fp_2009_43.pdf