Fire Smoke Damper for Shaft Enclosure

[crivera8]

Hello All,

We have an outside air duct that penetrates a rated shaft enclosure (shaft connects 4 floors) and the OA duct goes straight up to the roof and discharges to the outside. The OA duct does not connect into any other floor on the way up to the roof. My question is if a fire smoke damper is required at the shaft enclosure penetration or is there an exception since it goes straight to the roof without communicating with other floors?

This project is located in California in case that matters.

thank you for your responses.

Carlo

 

[Emrelug84]

Hello,

In your fire scenario, you may need to prevent outdoor air coming to the floor when fire occurs. In that case, you will need damper at the fresh air duct. Moreover, shaft connects to four floors and if you don't have smoke dampers at the duct connecting to the floor, smoke may have passed to the other floors some time later and it spreads. In this case, you have to put dampers.

You can avoid the fire/smoke damper at the shaft penetration if all of the following are true:
• You have a vertical shaft with exhaust ducts entering the shaft on every floor (such as in a high-rise hotel or dormitory),
• You build steel sub-ducts that extend vertically upward into the vertical riser by at least 22 inches,
• And if there is a continuous flow of air upward to the outdoors (e.g., the exhaust fan is on the roof and is always on).
• In some jurisdictions, the fan must be on emergency power for this exception to qualify.

 

[crivera8]

Thank you Emrelug84 for your response.

I wanted to clarify more of how this shaft enclosure is being used. The shaft enclosure contains a variety of ducts for exhaust, relief, and outside air. The shaft does not have moving air, only the ducts inside the shaft do. The existing ducts in the shaft that connect into each floor have a fire smoke damper at the branch going into each floor to keep smoke/fire from communicating between floors.

I had heard of the exception you mention and have used it in dorm room buildings, although for this situations we don't have a fan at the roof that exhausts the air in the shaft, we only have individual duct systems in the shaft.

So I have a follow up question to one of your comments:

"Moreover, shaft connects to four floors and if you don't have smoke dampers at the duct connecting to the floor, smoke may have passed to the other floors some time later and it spreads. In this case, you have to put dampers."

All other duct branches on the other air systems in the shaft enclosure have fire smoke dampers at their shaft penetrations to the floor, and the this new fresh air duct does not communicate with other floors. The fire scenario I understand is if there is a fire on the floor the new OA duct is penetrating, the smoke/fire would only have a path up to the roof/outside. If there is a fire on another floor the smoke/fire cannot communicate to other floors as the duct systems communicating those floors have fire smoke dampers at the branch on each floor. Are you saying that the smoke will be able to exit a duct and go into the empty shaft space and therefore other spaces/floors?

I really appreciate the help. These fire/smoke damper scenarios are tricky.

Thank you,

Carlo

 

[Emrelug84]

Hello Carlo,

Smoke can exit the duct and fill the shaft with smoke if you do not have damper. Moreover, the outside air duct is not smoke exhaust duct. Therefore, it is not allowed to use this duct as smoke exhaust system duct in fire condition. In fire scenario, outside fresh air may be prevented to go into the room, that is why damper is necessary to block the outside air penetration.
If the duct you mentioned was exhaust duct, standarts can be read again and find appropriate solution but it is fresh air duct and there is no exception for that in IBC (International Building Code).

Best Regards,

Emre

 

[crivera8]

Thank you very much Emre. This cleared up my confusion.

Appreciate you taking the time.

Best,

Carlo

 

[DrRTU]

If the roof assembly is not rated, then you need a fire damper at the OA duct penetration at the bottom of the rated shaft. A SFD could be applied but a FD with the correct rating should meet your requirements. I have seen a roof rating issue such a parking garage in which the shafting must be protected from above or external to the building.
SP