Limited combustible material above suspended ceiling.

[SprinklerDesigner2]

We have an older strip mall project constructed mostly of concrete block, bar joists and metal roof deck.

Upon removal of existing ceiling tiles we found what I would call a small bit of combustible material above the ceiling as shown in this photo.

http://img525.imageshack.us/img525/6510/woodsb9.jpg

The local fire official thinks sprinklers might be required and while I agree it got me to wondering what exactly is the definition of "limited"?

Question to the experts: In your opinion would the amount of cumbustible material you see contribute to a fire threat?

Thanks

 

[cdafd]

that seems to be pushing it a little.

is the wood doing any good up there, or can a saws all take care of the problem???

 

[SprinklerDesigner2]

cdafd,

I agree seems to be pushing it a bit. I don't see where the diagonal members are doing anything so a saws all would take care of the problem.

I would have to think the vertical members, mostly behind drywall but some exposed, would easily fit the criteria for "limited".

 

[FFP1]

I am a registered FPE and I worked for FM Global for ~15 years.......the small wood frame structure in the center of the picture (45 degree angle) is the definition of limited combustible construction. The wood frame structure in this picture with the above described building construction does not warrant sprinkler protection. The anticipated fire would be a relatively slow burning incident due to the open array and fire fighters would easily extinguish the fire with hose streams. A fire involving this small wood frame structure would not result in an uncontrolled fire incident as long as the small wood frame structure shown in the picture is the only continuous combustible construction which could be involved on a fire.

HOWEVER......the wood frame concealed space (which is difficult to see behind the gypsum) looks like it might warrant sprinkler protection if the space is continous and has as much wood frame construction as the picture suggests. This area appears to be deeper than a standard wood frame wall. This area would trap heat, allow quick fire propagation and would also be very difficult for fire fighters to extinguish IF the continuous area is significant in size.

I hope this helps.

 

[rwatters]

Hope you don't mind the piggyback, but I have another drop-ceiling question...

The building is fully sprinklered and the space is currently empty and without a drop ceiling. A FLOATING ceiling is being added, meaning it is a drop ceiling where the edges of the drop ceiling don't meet the walls. Does it require sprinklers above and below or can the existing heads just be dropped through the new drop ceiling?

I've attached an interior elevation showing the ceiling arrangement. Note, the two interior offices you are looking at do not have their own ceiling.

FYI, I'm a mechanical design engineer. We have a sprinkler engineer that we've started outsourcing to, but we've had problems with his interpertation of the code.

Thanks.

 

[rwatters]

Here's a picture of the space. The elevation in the previous pic is looking toward the wall to the right. Btw, the space is being converted to one large open office (with the exception of the two little offices shown).

 

[cdafd]

rwatters

cannot tell what the existing ceiling is made out of, but looks non com.

you do not specify waht the gap will be????

I have required sprinklers above and below, when you have a "cloud effect", also saw one install where there was about 2-3 foot gaps and the solution was a sprinkler head in the gap with a shield, did not agree with the shield option.

 

[rwatters]

Sorry, yes, the existing ceiling (just the deck of the next floor) is concrete/steel.

There are two "cloud" heights: 11' and 12'6" and the deck above is 14', so the gaps are about 3' and 18".

 

[TravisMack]

I hate when architects do this, but it seems to be in fashion now. I have seen this handled multiple ways:

1 - Sprinklers at the roof deck above and in the cloud ceilings. A fair amount of work, but seems to be the most conservative and acceptable. Afterall, you can only eliminate sprinklers in 'concealed' non combustible spaces. When you have the perimeter open, the space is no longer concealed. NFPA states that openings such as return air grills do not create a non concealed space. But, the typical RAG is 2'x2' or 4 sq ft. The most I have seen is 2 RAGs together, for a total of 8 sq ft. I figure that if the opening is more than 8 sq ft, then you do not have a concealed space.

2 - Sprinklers in the ceiling and then extending for a length of 15' beyond the open gap. Depending on the size of the room, it may mean fully sprinklered at the deck, or just in a certain area. One job that sticks out where this was done was an office building where there was no ceiling in the halls, but drop ceilings in all of the offices. None of the walls went to the deck. So, sprinklers were placed to protect 15' on both sides of the corridor at the roof deck and in the ceilings at the offices.

3 - Sprinklers placed at the gap at the level of the cloud. Sometimes a pie plate (aka heat collector - but doesn't work) used on the sprinklers at the gap. Based on conversations with FM guys, this is completely useless and a waste of money.

I always recommend #1, but could see the rationale for option 2. Option 3 is a joke IMO. What is your sprinkler guys interpretation?

Travis Mack
MFP Design, LLC

 

[rwatters]

His interpretation is #1. In my ignorance of FP, I'm trying to apply logic to the situation and I was thinking that since the lower sprinklers will cover the entire floorspace and the area above the ceiling is noncombustable that there wouldn't be a good reason to have sprinklers above. And since we have had some issues with this consultant and the code is sufficiently vague, I wanted a second opinion. I appreciate it, guys.

 

[cdafd]

" - Sprinklers placed at the gap at the level of the cloud. Sometimes a pie plate (aka heat collector - but doesn't work) used on the sprinklers at the gap. Based on conversations with FM guys, this is completely useless and a waste of money."

thank you not an FPE but have never seen where this owuld work, and have been told the sheild can create turbulance and go by the head.

same idea with the gap it can go pass the gap and miss the head, no idea at what width that that could happen, but with a three foot opening kind of big.

 

[TravisMack]

No problem. It is often good to have a sounding board to bounce questions to.

Good luck!

Travis Mack
MFP Design, LLC