# 2000cfm and 15000cfm and duct smoke detectors



## mshields

Where would I find the rules pertaining to duct smoke detectors and when they are required.

And is it true that the IBC is in conflict with another code on this subject.  I'm told that the the IBC does not ever require supply side duct smokes.  It only requires Return side duct smokes when you have 2000cfm.

True?

Thanks,


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## Coug Dad

IBC / IMC is in conflict with NFPA 90 A regarding where the detectors are installed and if a smoke damper is required within the air handling unit.


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## Gregg Harris

mshields said:
			
		

> where would i find the rules pertaining to duct smoke detectors and when they are required.And is it true that the ibc is in conflict with another code on this subject.  I'm told that the the ibc does not ever require supply side duct smokes.  It only requires return side duct smokes when you have 2000cfm.
> 
> True?
> 
> Thanks,


imc 606.2.1


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## mtlogcabin

Coug Dad said:
			
		

> IBC / IMC is in conflict with NFPA 90 A regarding where the detectors are installed and if a smoke damper is required within the air handling unit.


 102.4 Referenced codes and standards.

The codes and standards referenced in this code shall be considered part of the requirements of this code to the prescribed extent of each such reference. Where differences occur between provisions of this code and referenced codes and standards, the provisions of this code shall apply.

NFPA 90 A is not a referenced standard within the I-Code family and therefore does not conflict with the code.


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## cda

this is from the 2003 edition of imc, but you can with a little work look at the current edtions via this link;;;

http://publicecodes.citation.com/

sorry for the broken english, but that is how it copies::

SECTION 606

SMOKE DE TEC TION SYS TEMS CON TROL

606.1 Con trols re quired. Air dis tribution sys tems shall be

equipped with smoke de tectors listed and la beled for in stallation

in air dis tribution sys tems, as re quired by this sec tion.

606.2 Where re quired. Smoke de tec tors shall be in stalled

where in dicated in Sec tions 606.2.1 through 606.2.3.

Exception: Smoke de tectors shall not be re quired where air

distribution sys tems are in ca pa ble of spread ing smoke beyond

the en clos ing walls, floors and ceil ings of the room or

space in which the smoke is gen erated.

606.2.1 Re turn air sys tems. Smoke de tectors shall be in -

stalled in re turn air sys tems with a de sign ca pacity greater

than 2,000 cfm (0.9 m3/s), in the re turn air duct or ple num

upstream of any fil ters, ex haust air con nec tions, out door air

connections, or de con tam i na tion equip ment and ap pli ances.

Exception: Smoke de tectors are not re quired in the re turn

air sys tem where all por tions of the build ing served by the

air dis tribution sys tem are pro tected by area smoke de tectors

con nected to a fire alarm sys tem in ac cordance with the

International Fire Code. The area smoke de tection sys tem

shall com ply with Sec tion 606.4.

606.2.2 Com mon sup ply and re turn air sys tems. Where

mul ti ple air-handling sys tems share com mon sup ply or return air ducts or ple nums with a com bined de sign ca pac ity

greater than 2,000 cfm (0.9 m3/s), the re turn air sys tem shall

be pro vided with smoke de tectors in ac cor dance with Sec -

tion 606.2.1.

Ex cep tion: In dividual smoke de tectors shall not be required

for each fan-powered ter mi nal unit, pro vided that

such units do not have an in dividual de sign ca pac ity

greater than 2,000 cfm (0.9 m3/s) and will be shut down by

activation of one of the fol lowing:

1. Smoke de tectors re quired by Sec tions 606.2.1 and

606.2.3.

2. An ap proved area smoke de tector sys tem lo cated in the

re turn air ple num serv ing such units.

3. An area smoke de tec tor sys tem as pre scribed in the exception

to Sec tion 606.2.1.

In all cases, the smoke de tec tors shall com ply with Sec -

tions 606.4 and 606.4.1.

606.2.3 Re turn air ris ers. Where re turn air ris ers serve two or

more sto ries and serve any por tion of a re turn air sys tem hav ing

a de sign ca pacity greater than 15,000 cfm (7.1 m3/s), smoke

detectors shall be in stalled at each story. Such smoke de tectors

shall be lo cated up stream of the con nection be tween the re turn

air riser and any air ducts or ple nums.

606.3 In stal la tion. Smoke de tectors re quired by this sec tion

shall be in stalled in ac cordance with NFPA 72. The re quired

smoke de tec tors shall be in stalled to mon i tor the en tire air flow

conveyed by the sys tem in clud ing re turn air and ex haust or re -

lief air. Ac cess shall be pro vided to smoke de tectors for in spection

and main te nance.

606.4 Con trols op er a tion. Upon ac tivation, the smoke de tectors

shall shut down the air dis tribution sys tem. Air dis tribution

sys tems that are part of a smoke con trol sys tem shall switch to

the smoke con trol mode upon ac tivation of a de tec tor.

606.4.1 Su pervision. The duct smoke de tectors shall be con -

nected to a fire alarm sys tem. The ac tuation of a duct smoke

detector shall ac tivate a vis ible and au dible su pervisory sig nal

at a con stantly at tended lo cation.

Exceptions:

1. The su pervisory sig nal at a con stantly at tended lo cation

is not re quired where the duct smoke de tec tor ac tivates

the build ing’s alarm-indicating ap pli ances.

2. In oc cu pan cies not re quired to be equipped with a fire

alarm sys tem, ac tu a tion of a smoke de tec tor shall ac tivate

a vis i ble and an au di ble sig nal in an ap proved lo -

ca tion. Duct smoke de tec tor trou ble con di tions shall

activate a vis ible or au di ble sig nal in an ap proved lo cation

and shall be iden tified as air duct de tec tor trou ble.


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## mshields

Thank you all!


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## Coug Dad

mtlogcabin said:
			
		

> 102.4 Referenced codes and standards.The codes and standards referenced in this code shall be considered part of the requirements of this code to the prescribed extent of each such reference. Where differences occur between provisions of this code and referenced codes and standards, the provisions of this code shall apply.
> 
> NFPA 90 A is not a referenced standard within the I-Code family and therefore does not conflict with the code.


I agree that NFPA 90A is not reference adopted by the IBC.  However, many jurisdictions blindly adopt "NFPA" and that can create the conflict on a local level.  Also, healthcare subject to CMS or Joint Commission have to follow NFPA 101 which does reference NFPA 90A creating a conflict.  I also agree that the most restrictive would generally apply.  However if one code's theory is to put detectors in the supply and the other code wants to put them in the return, which is more restrictive?  Doing both is a waste of money.


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## steveray

Good point CD...and good discussion......



			
				Coug Dad said:
			
		

> I agree that NFPA 90A is not reference adopted by the IBC.  However, many jurisdictions blindly adopt "NFPA" and that can create the conflict on a local level.  Also, healthcare subject to CMS or Joint Commission have to follow NFPA 101 which does reference NFPA 90A creating a conflict.  I also agree that the most restrictive would generally apply.  However if one code's theory is to put detectors in the supply and the other code wants to put them in the return, which is more restrictive?  Doing both is a waste of money.


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## Builder Bob

mshields -

The thought process for the IMC is to sample undiluted air that is pulled into the unit(return) - NFPA often requires the duct detector to be placed in the supply.

I am not sure why IMC and NFPA would be in direct contrast with each other...... However, in IMC land, be sure the duct detector is placed in the return prior to any outside make up air (fresh air).


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## cda

Not a deep thinker on Mionday's, but what is the reason for the duct detector???  shut down the unit, and not fire somewhere else in the duct work or rooms served ??? and why would you want to shut down the unit?? fire in the unit itself??

so if the idea is that you want to shut down the  unit itself,,,, where is the best location for the duct detector before????? or after the unit???  seems like on the side blowing air out of the unit would be the best placement?????????????


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## klarenbeek

The reason for the duct detector to shut down the unit is so the air handling system doesn't spread smoke from one area of the building to another, since smoke actually kills more people than fire itself. My guess is that the intent of the IMC putting it in the return instead of the supply is that it does not get diluted by outside air brought in through the air handler.  If the building has a fire alarm system, the duct detector has to be connected to it.


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## cda

KLA   good points

Dilution: If outside air mixes with circulated air, it can dilute

combustion particle concentration and prevent a detector

from sensing a fire. Remember that detectors alarm only when

combustion particles constitute a specified percentage of air

being sampled. To avoid dilution, detectors should be located

before fresh air intakes and before the exhaust air output.

http://www.systemsensor.com/pdf/A05-1004.pdf

So why is there such a difference in requirements? There are two schools of thought concerning the purpose of duct detectors. There have been numerous unsuccessful proposals over the last couple of I-Code cycles to change the IMC requirements to match the NFPA 90A requirements. The primary purpose of the duct detector on the supply side is to shut down the air handler if fire is detected in the fan or filter. This would protect the equipment and keep smoke from being distributed to the air conditioned space. Some would argue that detectors on the supply side are susceptible to outside air or smoke, which could affect the operation of the supply side smoke detector. There also is the problem of false alarms due to dust accumulation on heat strips in the AHU burning off when heaters are turned on and activating the smoke detector. For this reason, both the IMC and NFPA 72 allow duct smoke detectors to initiate a supervisory signal rather than an alarm signal.

http://www.ecmag.com/?articleID=12361&fa=article


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## klarenbeek

That would make too much sense to have both standards have the same requirement! When I was an HVAC installer in the 90's we were under the UMC, and at that time we had to install them in the supply. I still occasionally get calls from electricians asking where the duct detector needs to go, even 10 years after we switched to the I-codes.  I see some large jobs where the engineer calls for detectors in both the supply and return.

One question I would raise is that if one of the reasons for installing detectors in the supply side is to detect smoke from a fire in the unit itself, why does NFPA 90 still have the exception not requiring detectors if the air handler only serves one room? The smoke inside the unit would still get blown into the occupied space, say, a church full of people.  I know my church would meet this exception, I did the HVAC inspections on it when it was built. (The DP called for them, so they were installed even though not required by code)


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## cda

klarenbeek said:
			
		

> That would make too much sense to have both standards have the same requirement! When I was an HVAC installer in the 90's we were under the UMC, and at that time we had to install them in the supply. I still occasionally get calls from electricians asking where the duct detector needs to go, even 10 years after we switched to the I-codes.  I see some large jobs where the engineer calls for detectors in both the supply and return.One question I would raise is that if one of the reasons for installing detectors in the supply side is to detect smoke from a fire in the unit itself, why does NFPA 90 still have the exception not requiring detectors if the air handler only serves one room? The smoke inside the unit would still get blown into the occupied space, say, a church full of people.  I know my church would meet this exception, I did the HVAC inspections on it when it was built. (The DP called for them, so they were installed even though not required by code)


the idea is if it is one big open room, people would see the smoke and hopefully leave!!!!!!!!!!!!!


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## mtlogcabin

klarenbeek said:
			
		

> The reason for the duct detector to shut down the unit is so the air handling system doesn't spread smoke from one area of the building to another, since smoke actually kills more people than fire itself. My guess is that the intent of the IMC putting it in the return instead of the supply is that it does not get diluted by outside air brought in through the air handler. If the building has a fire alarm system, the duct detector has to be connected to it.


Agree and in some scenarios you could be bringing in 100% fresh air and the location of a duct detector would be mute. However the majority of the time the return prior to the introduction of fresh air would be the best location for a duct smoke detector to determine if there is smoke in the building.


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