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Duct Smoke Detectors
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Re: Duct Smoke Detectors By  dfrcinspector

Posts: 0

7/1/2002 4:33:00 PM

Section608.
"Automatic shutoff shall be accomplished by interrupting the power source of the air-moving equipment upon detection of smoke in the "MAIN SUPPLY-AIR DUCT"
served by such equipment."
The main suppy-air duct is the duct which is connected to the main air-moving equipment.
I dont know your situation, but I would assume that the VAV is probably connected to a lateral duct suppling air to a space.
Or if the VAV is tapped off of the main duct it would be a lateral supply.
No smoke detector required.


   

Re: Duct Smoke Detectors By  Sam Suh

Posts: 0

7/2/2002 4:36:00 PM

I have a different view. Fan powered VAV is an air-moving system per UMC 203 definitions-air-handling unit/air-moving system.
Section 608 -the automatic shutoff shall be accomplished by interrupting the power source
of THE(fan powered VAV) air-moving equipment upon detection of smoke in the main supply-air duct served by SUCH(the fan powered VAV) equipment. But in this case it should not require automatic shutoff because the fan powered VAV is less than 2000 cfm.


   

Re: Duct Smoke Detectors By  maniac

Posts: 0

12/8/2003 11:59:00 AM

? The International Mechanical Code (2000) and the NFPA 90A (1999) differ primarily in the requirement that when an HVAC unit has a capacity of greater than 2000 cfm:
? The IMC requires that the duct smoke-detector be placed on the return side of the unit.
? NFPA 90A requires that the duct smoke-detector be placed on the supply side of the unit.
? Additionally, the IMC addresses the issue of VAV zone units and/or VAV-type fan powered terminal units.

? It will be up to jurisdictions on a state or local level to adopt either the ICC or NFPA codes which best fits their requirements. With specific concern to the use of duct smoke detectors, the following points apply to both the IMC and NFPA 90A.
Both codes allow the use of area smoke detectors to meet the requirements of shutdown interface for applicable HVAC units. In fact, NFPA 72 (1999(the ?Standard? cited by both codes), A-2-10.1 states that areas detectors should be used in lieu of duct-type smoke detectors due to the effects of dilution in the ductwork.

? Contact you BO.


[This message has been edited by maniac (edited 12-08-2003).]


   

Re: Duct Smoke Detectors By  maniac

Posts: 0

12/8/2003 11:59:00 AM

? The International Mechanical Code (2000) and the NFPA 90A (1999) differ primarily in the requirement that when an HVAC unit has a capacity of greater than 2000 cfm:
? The IMC requires that the duct smoke-detector be placed on the return side of the unit.
? NFPA 90A requires that the duct smoke-detector be placed on the supply side of the unit.
? Additionally, the IMC addresses the issue of VAV zone units and/or VAV-type fan powered terminal units.

? It will be up to jurisdictions on a state or local level to adopt either the ICC or NFPA codes which best fits their requirements. With specific concern to the use of duct smoke detectors, the following points apply to both the IMC and NFPA 90A.
Both codes allow the use of area smoke detectors to meet the requirements of shutdown interface for applicable HVAC units. In fact, NFPA 72 (1999(the ?Standard? cited by both codes), A-2-10.1 states that areas detectors should be used in lieu of duct-type smoke detectors due to the effects of dilution in the ductwork.

? Contact you BO.


[This message has been edited by maniac (edited 12-08-2003).]


   

Re: Duct Smoke Detectors By  cda

Posts: 0

3/3/2008 6:58:00 AM

IMC, edtion ahj is under

have inspector site section and than review said section to see if it valid or not


   

Re: Duct Smoke Detectors By  doughill3

Posts: 0

3/3/2008 7:12:00 AM

The following citation was transmitted:
909.19.2 Duct Smoke Detectors.
Where multiple air-handling systems share common supply or return air ducts or plenums with a combined design capacity greater then 2000 cfm, the return air system sha11 be provided with smoke detectors. (No title to code reference given.)
I believe the AHJ is defining each "fire area" as a supply/return "plenum". Hence the requirement that all my HVAC must have duct detection.


   

Re: Duct Smoke Detectors By  Paul Sweet

Posts: 0

3/3/2008 8:13:00 AM

Sounds like he''s trying to stretch the code way beyond its intent. I think this section was intended to apply to a store or large meeting room served by mulitple units, or to buildings where walls stop at the ceiling, and the ceiling return plenum serves more than one unit.

Chapter 2 of the 2003 IMC defines Plenum: "An enclosed portion of the building structure, other than an occupiable space being conditioned, that is designed to allow air movement, and thereby serve as part of an air distribution system."


   

Re: Duct Smoke Detectors By  lockek

Posts: 0

3/3/2008 8:17:00 AM

The following is a copy of the text I recieved from an NFPA staff member regarding this subject:

You state that you''ve got two or more HVAC systems (less than 2,000 cfm each) are serving a common open air room. Your first question is; "Would this section of the current NFPA 90A require that we treat all of the units serving this common open air area as one system and calculate the sum total of all units in this area to obtain the system cfm?" And your second question is; "If so, would the duct smoke detectors require to be interlocked so that when one detector went into alarm all of the common area units shutdown as well?"



The answer to the first question is "no". By definition, an "Air Distribution System" is "a continuous passageway for the transmission of air that, in addition to air ducts, can include air connectors, air duct fittings, dampers, plenums, fans, and accessory air-handling equipment but that does not include conditioned spaces.(emphasis added)" It is not unusual for a large conditioned (occupied) space to have multiple air distribution systems. The key is the path the air follows once it leaves a conditioned (occupied) space until it is returned to a conditioned (occupied) space. That entire path is one air distribution system.



The exact wording in 90A that requires detectors and "shutdown" is: "Downstream of the air filters and ahead of any branch connections in air supply systems having a capacity greater than 944 L/sec (2000 ft3/min)". The words "having a capacity greater than 944 L/sec (2000 ft3/min)" modify the term "air supply systems". Any individual air distribution system that''s less than 2000 cfm, regardless of how many other air distribution systems serve the same conditioned (occupied) space, doesn''t need "isolation" smoke dampers with smoke detector initiation and unit shutdown.

I hope this clarifies the requirement for you.



Sincerely,



Allan B. Fraser, CBI, CPCA

Senior Building Code Specialist

Building Fire Protection and Life Safety



ABF/lc#5074



Important Notice: This correspondence is not a Formal Interpretation issued pursuant to NFPA Regulations. Any opinion expressed is the personal opinion of the author, and does not necessarily represent the official position of the NFPA or its Technical Committees. In addition, this correspondence is neither intended, nor should be relied upon, to provide consultation or services.


   

Re: Duct Smoke Detectors By  cda

Posts: 0

3/3/2008 10:03:00 AM

Appears the congressman from the great state of Florida is correct, ken12000

not sure where he is gettin the reference "909.19.2 Duct Smoke Detectors" maybe there is something in there that we do not know


   

Re: Duct Smoke Detectors By  Dr. J

Posts: 0

3/3/2008 10:11:00 AM

It is not clear to me from the OP if there are multiple FC units in a common plenum, or if the non-rated walls extend to the structure without any transfer between FC units.

For ammo, please confirm code and year being enforced. The 909 citation is not valid for IMC (909 is for Vented Wall Furnaces). It is also not valid for NFPA 90A (it only has 7 chapters). NFPA 90A is only valid if the AHJ has adopted it, or has adopted NFPA 101 and by extension NFPA 90A.

So, assuming this is under IMC (since the OP referenced ICC), 606.2.2 states:

"[i]606.2.2 Common supply and return air systems.
Where multiple air-handling systems share common supply or return air ducts or plenums with a combined design capacity greater than 2,000 cfm (0.9 m3/s), the return air system shall be provided with smoke detectors in accordance with Section 606.2.1.
Exception: Individual smoke detectors shall not be required for each fan-powered terminal unit, provided that such units do not have an individual design capacity greater than 2,000 cfm (0.9 m3/s) and will be shut down by activation of one of the following:
1. Smoke detectors required by Sections 606.2.1 and 606.2.3.
2. An approved area smoke detector system located in the return air plenum serving such units.
3. An area smoke detector system as prescribed in the exception to Section 606.2.1.
In all cases, the smoke detectors shall comply with Sections 606.4 and 606.4.1."[/i]

The operative words are "...common supply or return air ducts or plenums...". Use Paul''s reference to the definition of a plenum, which does not mention any ratings, just "enclosed". This means that separate systems are delineated by any enclosure, such as sheet metal ducts or non rated construction.

If the individual units are not separated/enclosed, they form a common return system and you do indeed need to deal with smoke detection and shutdown for all units. You should review the entire section 606, because there are several exceptions to needing the shutdown (if units can''t transfer smoke beyond the room of origin), and several methods to achieve the required shutdown besides a duct detector for each unit (plenum detectors, area detectors).


   

Re: Duct Smoke Detectors By  doughill3

Posts: 0

3/3/2008 10:55:00 AM

Thank you gentlemen.

The AHJ is using IMC,IBC, and IFC 2006.

I have available to me IBC & NFPA-1 2003, and an older NFPA 90A.

Chapter 9, IBC 2003 does not list duct detection as a requirement for my occupancy "E" (day care). 909 is concerned with Smoke Control Systems, which we do not have.

The FCU are all ducted supply and return. There is no common plenum or duct between any FCU. The rooms are walls to structure with either gyp to structure, or grid/tile.

There is one instance in which two separate FCU supply a common room, (both are separately ducted), and only one FCU picks up return from the common room.


   

Re: Duct Smoke Detectors By  cda

Posts: 0

3/3/2008 12:50:00 PM

if they use IMC than that is where the requirements are

they may have sited the wrong section


   

Re: Duct Smoke Detectors By  Dr. J

Posts: 0

3/3/2008 2:51:00 PM

I missed the ducted return part of your OP. My bad (could have saved a bunch of typing). Individually ducted returns = not a common return systerm = do not need DD on FC < 2000 cfm.


   

Re: Duct Smoke Detectors By  John Kopp

Posts: 0

3/3/2008 8:27:00 PM

It?s funny how they used 2,000 CFM as the threshold. One would think this means 5 ton sized A/C equipment or larger IE 400 CFM per ton X 5 = 2,000. Then you take into account static system pressures and review blower performance tables based on system static and A/C?s will work down to 350 CFM per ton etc. So one could argue their 5 ton system is really operating at 1,950 CFM and it probably is so this is not required.

They should have included the following text ?and or nominal 5 ton sized systems or larger?. I have had some Inspectors look at 4 ton equipment and deside smokes were needed because blower tabels showed CFM?s up to 2,000.

I think code intent was for 5 ton equipment or larger.

John


   

Re: Duct Smoke Detectors By  John Kopp

Posts: 0

3/3/2008 8:27:00 PM

It?s funny how they used 2,000 CFM as the threshold. One would think this means 5 ton sized A/C equipment or larger IE 400 CFM per ton X 5 = 2,000. Then you take into account static system pressures and review blower performance tables based on system static and A/C?s will work down to 350 CFM per ton etc. So one could argue their 5 ton system is really operating at 1,950 CFM and it probably is so this is not required.

They should have included the following text ?and or nominal 5 ton sized systems or larger?. I have had some Inspectors look at 4 ton equipment and deside smokes were needed because blower tabels showed CFM?s up to 2,000.

I think code intent was for 5 ton equipment or larger.

John


   

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