# CBC and CMC regarding fire dampers



## Meyer (Feb 7, 2020)

From CBC: Fire dampers and combination fire/smoke dampers are not required in kitchen and clothes dryer exhaust systems where _dampers_ are prohibited by the _California Mechanical Code_.

Where in the calif code does it say about kitchen not having dampers? And what is the reason for this?


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## cda (Feb 7, 2020)

Guess


May not work and back smoke up in to room??


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## rgrace (Feb 10, 2020)

That's a good question. I am more familiar with the International Codes than with the Uniform Codes, but I will give this a shot; they are similar  

504.4 of the CA Mechanical Code (CMC) is somewhat clear that fire/smoke dampers cannot be installed in a clothes dryer exhaust duct (commercial or domestic).

CMC 504.3 _does not_ prohibit fire/smoke dampers from being installed in a domestic kitchen exhaust duct. I cannot find any other location in the CMC or the IMC that actually prohibits the installation of a fire/smoke/radiation damper in a domestic kitchen exhaust duct. 

For a commercial kitchen exhaust duct, CMC 510.1.3 is somewhat the equivalent to IMC 506.3.7 except that 510.1.3 is missing the first sentence of 506.3.7 that says "Duct systems serving a Type I hood shall be constructed and installed so that grease cannot collect in any portion thereof." IMC _implies_ that a fire/smoke damper cannot be installed because it will collect grease. CMC refers to NFPA 96 for it's commercial kitchen ventilation systems, the prohibition of fire/smoke dampers may be there for commercial kitchens.

Chapter 7 of the CBC _and the_ IBC both need a lot of work. There are many examples like this that just leaves the reader confused.


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## cda (Feb 10, 2020)

rgrace said:


> That's a good question. I am more familiar with the International Codes than with the Uniform Codes, but I will give this a shot; they are similar
> 
> 504.4 of the CA Mechanical Code (CMC) is somewhat clear that fire/smoke dampers cannot be installed in a clothes dryer exhaust duct (commercial or domestic).
> 
> ...




Neither one is mechanical/ automatic

So a damper may or may not open?


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## Meyer (Feb 10, 2020)

rgrace said:


> That's a good question. I am more familiar with the International Codes than with the Uniform Codes, but I will give this a shot; they are similar
> 
> 504.4 of the CA Mechanical Code (CMC) is somewhat clear that fire/smoke dampers cannot be installed in a clothes dryer exhaust duct (commercial or domestic).
> 
> ...


Yes, I agree. I also found CMC 505.6.1 says that fire dampers must not be installed where toxic hazard is greater than the fire hazard. Do you think kitchen fumes are more toxic than smoke/fire?


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## cda (Feb 10, 2020)

Meyer said:


> Yes, I agree. I also found CMC 505.6.1 says that fire dampers must not be installed where toxic hazard is greater than the fire hazard. Do you think kitchen fumes are more toxic than smoke/fire?



Depends

Gas stove maybe, but when a person is blackening a fish or steak, or walks away and stuff cooking catches on fire. You do not want all that smoke to stay inside the room


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## Yikes (Feb 10, 2020)

Meyer said:


> Yes, I agree. I also found CMC 505.6.1 says that fire dampers must not be installed where toxic hazard is greater than the fire hazard. Do you think kitchen fumes are more toxic than smoke/fire?



If the purpose of the kitchen exhaust is to remove products of combustion including carbon monoxide form a gas stove.  However: 
1.  Nothing that I know of in the codes requires a ducted range hood for a dwelling unit's gas range.  Recirculating hoods are acceptable.  
2.  The codes do require carbon monoxide detectors, which help to mitigate the hazards associated with using gas appliances in a dwelling unit.
On the basis of those two items, I'm guessing that the codes currently consider a fire spreading via ductwork to be a greater hazard than CO poisoning from a gas cooking appliance.


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## Paul Sweet (Feb 11, 2020)

Grease buildup on a kitchen exhaust damper or lint buildup on a dryer exhaust damper are major fire hazards themselves, as well as interfering with proper operation of a fire damper.


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## rgrace (Feb 12, 2020)

All good points, but no code section prohibiting a damper from being installed in a domestic kitchen exhaust duct. Grease buildup on a kitchen exhaust damper is apparently acceptable on UL 710 listed hoods under YXZR _Exhaust Hoods with Exhaust Dampers_. If the domestic kitchen exhaust duct were to penetrate a fire-resistance rated assembly, protection of that penetration will be required. If a damper were prohibited, the protection would be a shaft per CBC 717.



Meyer said:


> Yes, I agree. I also found CMC 505.6.1 says that fire dampers must not be installed where toxic hazard is greater than the fire hazard. Do you think kitchen fumes are more toxic than smoke/fire?



CMC Section 505 is titled _Product-Conveying Systems_. Domestic range hoods is listed under CMC Section 504 _Environmental Air Ducts_. If CMC 505.6.1 were applicable to domestic range hoods (or even clothes dryer exhaust), that (those) section(s) would fall under Section 505, not 504. These are considered environmental air ducts, not product-conveying ducts per Chapter 2 definitions. The domestic range hood would have to convey air temperatures exceeding 250 degrees to qualify for product conveying.


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## Builder Bob (Feb 17, 2020)

You won't find the answer in the code  - it is going to be dependent upon the manufacture listing of the Hood System..... I know of one hood system with fire suppression that require exhaust to close for proper operation of grease duct extinguishment. Weird and really expensive hood system with water suppression and wash/clean cycle built in. Only have seen it one time.........


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## John shane (Feb 18, 2020)

Hi guys, I am designing for a 3 storey apartment.
My domestic kitchen hood needs exhaust and it will be through the roof using a fire rated shaft of 1 hr rating that will run from first to third floor. 
Now my domestic kitchen hood duct needs to penetrate this shaft at every floor, do I need fire dampers when they penetrate the shaft wall? If so, why and is it permitted by code?
If no, also why?


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## rgrace (Feb 21, 2020)

Hi John, nowhere in this string has a code section been provided that will prohibit a fire/smoke/radiation damper from being installed in a domestic kitchen hood exhaust system. FYI, don't forget the smoke damper in your shaft penetration(s) per CBC 717.5.3. I run into apartments/condos that want to terminate their kitchen exhaust through the exterior wall. They penetrate the ceiling membrane of a floor/ceiling assembly, turn 90 degrees and run to the exterior wall. I enforce CBC 717.6.2 language and require a ceiling radiation damper at the membrane penetration.


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## klarenbeek (Feb 24, 2020)

Not sure about the CMC, but the 2018 IMC does address common domestic kitchen exhaust systems in multistory structures in section 505.5. Its a somewhat lengthy section that prohibits dampers other than backdraft dampers at the hood, with the shaft penetrations being protected by subducts. It was new in the 2015 IMC, and is similar to the setup for multistory domestic dryer common duct systems.


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## rgrace (Feb 25, 2020)

klarenbeek said:


> Not sure about the CMC, but the 2018 IMC does address common domestic kitchen exhaust systems in multistory structures in section 505.5. Its a somewhat lengthy section that prohibits dampers other than backdraft dampers at the hood, with the shaft penetrations being protected by subducts. It was new in the 2015 IMC, and is similar to the setup for multistory domestic dryer common duct systems.



I was waiting to see if someone was going to bring this up. Keen eye for klarenbeek and kudos as well  However, this copy-and-paste job of 504.10 had unintentionally brought Number 2 with it in its entirety. This was an unnoticed consequence, and will likely be corrected in the future. If the intent was to prohibit dampers in all domestic kitchen exhaust ducts, that language would have been placed in 505.1 (just like 504.2 prohibits dampers), not placed specific only to _common exhaust systems in multistory structures_. Subducts are used in lieu of fire dampers (607.5.5 Exception 2). There is no practical reason that one of these common multistory domestic kitchen exhaust systems cannot contain a combination of subducts and fire dampers (i.e. subduct all units from one floor and fire damper all units from a different floor). The same level of protection is there. This example is prohibited for common multistory domestic dryer exhaust systems because 504.2 prohibits dampers in a dryer exhaust duct altogether.


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## ADAguy (Feb 25, 2020)

rgrace said:


> That's a good question. I am more familiar with the International Codes than with the Uniform Codes, but I will give this a shot; they are similar
> 
> 504.4 of the CA Mechanical Code (CMC) is somewhat clear that fire/smoke dampers cannot be installed in a clothes dryer exhaust duct (commercial or domestic).
> 
> ...



Then suggest to CBSC for their next round?


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## rgrace (Feb 26, 2020)

ADAguy said:


> Then suggest to CBSC for their next round?



Sorry, the acronym escapes me ...... Please verify.


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