# subducts



## peach (Oct 29, 2009)

The IMC allows the use of subducts to eliminate dampers.. how do you feel if the shaft *also* is the protection for structural steel?

thanks in advance


----------



## MechinspMi (Oct 30, 2009)

Re: subducts

Fire dampers only are excepted when sub duct method is used per 607.5.5 X1.1, doesn't say anything about anything else in the shaft.  Smoke dampers excepted only if B or R occupancy with fully protected by sprinkler system, also no mention of other items in shaft.  Guess it doesn't matter what we think about it, the Code is all we enforce, this case is Black & White and can't see any Grey lol

vern


----------



## Gene Boecker (Oct 30, 2009)

Re: subducts

peach, that must be a small building.

IBC Section 714.2.1 requires individual protection for columns if they support more than two floor or a floor and a roof.  If its three stories in height, individual protection is required and the shaft can't act as the protection.

So, to your question, assuming that its a small building, why not?

If the subducts are being used, its probably a residential building which is required to be sprinklered throughout.  It's also required to have a fire alarm.  Even if the sprinklers fail to control the fire, by the time the fire would get into the shaft and affect the column, people should be out of the building (and there are a whole lot of other problems since the sprinklers failed).


----------



## Dr. J (Oct 30, 2009)

Re: subducts

I may not be understanding the arrangement here, but does this comply with IBC 706.5 which requires "_The supporting construction for fire barrier walls shall be protected to afford the required fire-resistance rating of the fire barrier supported..._"?


----------



## AegisFPE (Oct 30, 2009)

Re: subducts

Another reference 714.2.1 would lead to is 714.3, as the duct sharing the shaft could probably be interpreted as an embedment or enclosure.


----------



## peach (Oct 30, 2009)

Re: subducts

well, as it turns out.. subducts wont work anyway.. the airflow is DOWN.  (It's a LEED thing).. the subducts were proposed as a relief for the amount of outside air..

Well the mechanical contractor isn't happy (the fire alarm guy is.. $$$)... it's going to be fire/smoke dampers at 150 locations.. the initiation location is still a question.. they are suggesting smoke detectors in the bottom of the shaft .. which makes sense.

This is a big darn school... renovation project.  The Make up air units are 23,000 cfm units.. and all equipment is located in a tunnel under the buildings (which is why sub ducts are out).

I'm not worried so much about the protection of the columns, since the shafts are built around them... and they've been there for 70 years


----------



## MechinspMi (Oct 31, 2009)

Re: subducts

Peach,

If you look at the requirements for detector location, don't have my books at home, I believe it states that the detector Must be within 5' of the smoke damper unless full area coverage is used as alternate method.  SOOOOOOOOOOOOOOOOo, Fire alarm guy will really be thrilled.

Had one of these in a high rise that when we were testing the 6th floor detectors with canned smoke, the detectors in the floor above and below activated prior to the 6th floor registering a signal and that is with the exhaust running.  Conclusion was that the smoke is denser and moves in all directions even with upward movement of the exhaust.  One reason I really don't like the sub duct method to start with.


----------



## peach (Oct 31, 2009)

Re: subducts

if the detector is within 5' of the lowest damper, and that detector activates all smoke dampers in that shaft, I still believe it's within the intent of the code.

We've tested hundreds of smoke detectors with canned smoke.. it doesn't take much to activate them.


----------

