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  1. #1
    Join Date
    May 2004
    Posts
    12,230

    Unhappy

    I posted this here because I want good coverage and feedback. Not everyone goes to the code section.

    Here it is...

    New Facility Manager comes to town. He hits me up with Standard Mechanical Code,

    Section 606, Smoke Detection Systems Control subsection 606.2.1

    Return air systems
    Smoke detectors shall be installed in the return air systems with a design capacity greater than 2,000 CFM (0.9M3/s), in the return air duct or plenum upstream of any filters, exhaust air connections, outdoor air connections, or decontamination equipment and appliances.
    Well, he hits me with the code change from 01-01-2001 and of course he is fresh out of engineering college.

    Supply air systems
    Smoke detectors shall be installed in the supply air systems with a design capacity greater than 2,000 CFM (0.9M3/s), in the return air duct or plenum upstream of any filters, exhaust air connections, outdoor air connections, or decontamination equipment and appliances.


    I am old school; I use only Ionization or Low-Flow Photoelectric. None of this fire stat stuff. I believe Ionization and Photoelectric smoke detectors work better in undiluted air mounted low in the return. This is the way I was brought up and I don’t understand why they changed the code. I also understand they are more sensitive this way and with an exhaust hood malfunction they will trip and cause a nuisance. All things being equal, and of course they are not, I believe in safety first and shutting down air handlers that circulate smoke in a public building should be shut as soon as possible.


    They come in the return air chamber by some of the Manufacturers. I have seen sampling tube end caps melted off because they were too close to the HX. I have also seen low voltage wiring melted for the same reason. (Hack install I know, but I have seen it) I have seen them mounted in both the return and supply at the same time and with or without alarm systems. Code 606.4.1

    Yes, I realize it is my job to keep up with all of the code changes but I wanted to know how you felt about this change. Is my thinking wrong?

    I await your replies with humility.

    Lusker





  2. #2
    Join Date
    Jun 2004
    Location
    Richmond Virginia
    Posts
    1,078
    I'm mostly on the service side of things and don't keep up with the code changes all the time. I thought it was 2,000 or above and you needed return. 8,000 or maybe it was 10,000 and you needed supply also. I actually try to get my equipment reps to help me keep up with all that stuff. They remind me that "you'll need an economizer with that", or the smoke detector, etc. It's add on items they can sell and they monitor the changes and advise me on how it will affect me.

  3. #3
    Join Date
    Nov 2001
    Location
    Seattle, WA
    Posts
    7,814
    In my area anything over 5 tons (2000 CFM) require smoke detectors in the return and supply. Properly placed they work well and will shut the unit down to keep from feeding the fire or disbursing the smoke.

    Problem I have is local fire dept needs smoke test on both dectors so I'm the one (I use too but not anymore) who would sit off a smoke bomb in the RA room and wait for the system to shut down. Then I had to go back in the smoke filled room, lite another smoke bomb off and hope the supply would trip. If not, I would have to keep doing this until it did.

    And we would have to, most of the time, put red indicator lights in the ceiling tile so you could see when and which detector goes off.

    The detectors actually work better mounted in the duct.
    "The American Republic will endure until the day Congress discovers it can bribe the public with the public's own money.
    - Alexis de Toqueville, 1835

  4. #4
    Join Date
    May 2004
    Posts
    12,230
    In Georgia and in 2001 the state aquired the Standard Mechanical Code book as their own.

    We don't need to have two in our systems here but I am not sure why they changed the code from return to supply air.

    I could fill this post and use tons of bandwith with reasons (excuses) why I don't concider the code should have been changed.

    I am being asked to change only 5 recently installed detectors to the supply. A reasonable request by the New FM. He is new to the trade and has little to no field experiance and we are not fighting about it. He could go back to a whole lot more units than that and ask that I swap them all out (on my dime, of course, and he would be within his rights)

    All units in the return are grandfathered in before 01-01-2001 but you guys that use the Standard Mechanical Code need to note the change.


    I am not looking for a pitty party. I am looking for someone to explain "WHY" and help me understand.



  5. #5
    Join Date
    Jun 2004
    Posts
    420
    Smoke detector in the return air is great if something in the room is burning and the smoke is being drawn into the unit. But, suppose the fire is in the unit itself - detector wouldn't go off until there is enough smoke in the room that it is drawn back into the return. Put the detector in the supply, and a fire within the unit is covered as well.

  6. #6
    Join Date
    May 2004
    Posts
    12,230
    Thanks D

    That is a good point. A first seasonal fire up on a dirty HX would trip it too, right?

    I could see a fire in the unit being a situation and I am shaking my head yes. I would think that the fire would kill the load and control wiring and shut it down too but much later and the SD would catch it first. Where there is fire there is smoke first. Very good point.

    I appreciate the input guys. Please keep it coming.

  7. #7
    Join Date
    Sep 2002
    Posts
    1,389

    supply smoke detectors

    It is a definite plus to have a supply side smoke detector rather than a return air detector:

    1. If the blower motor burns up, the supply side catched it.
    2. If the unit has economisers, and/or outside air, and a fire is in the surrounding area of the roof, the supply side will catch it. If the detector, in this instance, is in the return then the smoke drawn in from the roof will not be detected by the return side detector until the space has filled enough with smoke to get back to said return detector.
    Hope this helps.
    tom

  8. #8
    Join Date
    Sep 2002
    Location
    Deer Trail, CO
    Posts
    216
    An amusing note concerning smoke detectors. Fire season in the Rockies, you can hear the fire alarms in all the commercial buildings when the wind changes and the smoke is pulled into the OSA intakes. Have to disable the fire alarms systems to keep the buildings operational.
    Don't let your ego get in the way of a good decision

  9. #9
    Join Date
    Jul 2001
    Location
    Buffalo N.Y.
    Posts
    1,571
    Supply side detection has been the standard up here for over 20 yrs.
    If the system is activated the supply along with the return is shutdown if they are seperate units but for the same zones.

    The majority of these codes will reference NFPA 101, our are contrived from various NFPA, UL code sections.

  10. #10
    Join Date
    May 2004
    Posts
    368
    lusker, according to the ICC website Georgia is Statewide adopted on the International Mechanical Code. The IMC does not mention Supply side detectors just the return side.
    Are you sure he is quoting from the properly adopted code? The SMC I always thought was the Southern not Standard Mechanical Code. If in fact your under the IMC supply side detectors are NOT required.
    Vern P: 2003 MBC,MRC,IFGC,IFC
    An HVAC-Talk Michigan Chapter Mechanical Inspector, Jurisdiction-Ann Arbor

  11. #11
    Join Date
    May 2004
    Posts
    12,230

    Thanks for the replies guys

    Vern,
    That is what I thought too but....

    Here are copies of the paper work. I had to look for myself too.

    Georgia State Amendments to the Standard Mechanical Code (International Mechanical Code) and the adoptions. The IMC is a copyrighted work owned by the ICC


    http://home.earthlink.net/~lusk/Top%20Code%20sheet.pdf

    http://home.earthlink.net/~lusk/Code%20606.pdf

    Bobby
    It is now code so I am stuck with getting out of my old habbits and creating new.

    TWC

    Yes, it does help, thanks a lot

    mdp

    Change the alarms to dog whistles! Then sit back and watch from the high ground...

  12. #12
    Join Date
    May 2004
    Posts
    368
    Lusker, I read it and does appear they ammended just that section and changed from return to supply but didn't ammend the rest of the section is that correct?
    Is the building wired with smoke dectectors tied to a monitored fire alarm panel?
    Are the rooftops in question serving 1 single area and are the returns ducted? If so no dectors required in the duct per ICC formal interp.
    Also they deleted the verbage from upstream on in that sentence.
    You need to carefully read the entire section 606 to see the exceptions to the rules and not rely on just 606.2.1
    Vern P: 2003 MBC,MRC,IFGC,IFC
    An HVAC-Talk Michigan Chapter Mechanical Inspector, Jurisdiction-Ann Arbor

  13. #13
    Join Date
    May 2004
    Posts
    12,230
    Lusker, I read it and does appear they ammended just that section and changed from return to supply but didn't ammend the rest of the section is that correct?
    yes

    Is the building wired with smoke dectectors tied to a monitored fire alarm panel?
    no, they have their own audible alarm and flashing lights

    Are the rooftops in question serving 1 single area and are the returns ducted? If so no dectors required in the duct per ICC formal interp.
    They serve kitchen, bath, sales counter and dining areas depending on duct run and supply vent locations. (up to 4 RTU's, each over 5 tons, serving one building divided into sections) they are not what I would think as common supply and return air systems (606.2.2)they are returned seperately to each unit. It is single story so 606.2.3 does not apply.

    Also they deleted the verbage from upstream on in that sentence.
    You are to delete this sentence; "In the return air duct or plenum upstream of any filters, exhaust air connections, outdoor air connections or decontamination equipment and appliances.


    You need to carefully read the entire section 606 to see the exceptions to the rules and not rely on just 606.2.1
    I have read them several times and do see that the language was not changed for 606.2.2 (Exception) for area smoke detector and 606.2.2 (the "return" air system shall be provided with smoke detectors in accordance with 606.2.1 but these are not common air systems. Also 606.3 and 606.4 are in compliance


    Vern, I really appreciate you doing this and helping me think this through. I want to understand why they did this and make sure our work is always within code. All of you guys are being very helpful. Thanks a lot.

    If you see anything else, don't be shy.



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