Duct Smoke Detector Requirements

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charlie b

charlie b

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I have been asked (it?s a continuing education thing that my company is encouraging us to pursue) to learn more about fire detection and alarm systems, and to pass on what I learn to the rest of the group. Not an evil pursuit, I suppose, since fire alarm stuff is not a strong suit of mine, and I could stand some ?learnin? on this subject. The specific question I am pursuing at the moment is, ?When is fire detection (i.e., duct smoke detectors) required for mechanical equipment.?

Can anyone offer suggestions on information sources?
 
I know they are required, we have them all over campus and they integrated with the fan motors, fire alarm, and gas valves. I am thinking NFPA 90. I will check with the controls guy and fire alarm guy after lunch.

I type too slow, Ron already replied with NFPA 90.
 
I could not find any reference in NFPA 72 2007 edition for requierments, only installation details of how they are installed. Could be a State Building Code that has the info when they are needed in HVAC systems. I think any air handler unit, HVAC systems with 15,000 cfm or larger will require a duct smoke detector. That's how I have been designing. Ask your Mechanical dept Chief for the requierment, he should have info on BOCA, IBC, etc.

- JWC
 
JWCELECTRIC said:
I could not find any reference in NFPA 72 2007 edition for requierments, only installation details of how they are installed. Could be a State Building Code that has the info when they are needed in HVAC systems. I think any air handler unit, HVAC systems with 15,000 cfm or larger will require a duct smoke detector. That's how I have been designing. Ask your Mechanical dept Chief for the requierment, he should have info on BOCA, IBC, etc.

- JWC
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Well which codes are in effect in your jurisdiction? If it's the IMC, see section 606; anything over 2,000CFM the detector is on the return side. If you have NFPA 90 anything over 2,000 CFM the detector is on the supply side. You got both? Congratulation! Two detectors!
 
Well the guys at work were no help. They only know its somewhere in NFPA 90. They said I should ask the engineer. LOL. Did I ever mention a lot of the guys I work with are bloody drones.

Anyways, I did find 6.4.2.1 in NFPA 90 2009 as a place to start. It shows the 15,000 cfm and 2000 cfm rules stated above.

Sorry I could not come up with anything useful.
 
BTW, I used the exception to 606.2 a lot.


606.2 Where required. Smoke detectors shall be installed where indicated in Sections 606.2.1 through 606.2.3.
Exception: Smoke detectors shall not be required where air distribution systems are incapable of spreading smoke beyond the enclosing walls, floors and ceilings of the room or space in which the smoke is generated.
 
ron said:
BTW, I used the exception to 606.2 a lot.


606.2 Where required. Smoke detectors shall be installed where indicated in Sections 606.2.1 through 606.2.3.

Exception: Smoke detectors shall not be required where air distribution systems are incapable of spreading smoke beyond the enclosing walls, floors and ceilings of the room or space in which the smoke is generated.
Click to expand...

Shoot, that would pretty much eliminate the need for duct smokes in large retail. A typical Lowe's will have 20 - 25 RTUs with duct smokes.:cool:
 
Code minimums aside, duct smokes keep you from pushing smoke around. They are a good idea for local shut down, generating a supervisory alarm. Smoke kills more and faster than the fire itself. A single duct smoke generating an alarm is a huge false alarm problem. Some FD's like to increase their call volume by requiring more devices that generate alarm, proper engineering and common sense aside.

Having said that, they are a pain and I hate them. Its a bit counter intuitive, but I would rather have the HVAC techs dealing with them over me crawling around in RTU's in two feet of snow or 110 F weather on a roof with one point of access 300' away, down a 30' ladder. (add emphasis for me whining here)

Charlie, one design consideration is placing the duct smokes below the roof line, not in the RTU itself. Now, this cannot be accomplished everywhere and it does make getting into the ceiling, or the need for a lift to access it an issue. Certain installs would necessitate it. I feel, from a MRO standpoint, outside the unit is better, even if a bit more challenging to access. If its dark, snowing, or raining, I am not working on them outside. If they are inside, I have nothing to complain about (I do, but I wont)
 
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