CMC · California Mechanical Code
Which dampers are required and what standards apply (fire, smoke, ceiling radiation)?
In short: California’s Mechanical Code requires smoke dampers to be listed to UL 555S, fire dampers to be listed to UL 555 and labeled/tested for airflow, ceiling radiation dampers to be listed to UL 555C or tested with the assembly (ASTM E119/UL 263), and combination units must meet both fire and smoke standards. Install per the damper listing and manufacturer’s instructions and follow the CMC §606.1–606.4 rules and the inspection/testing references in §606.6.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
In the California Mechanical Code, smoke dampers must meet UL 555S (§ 606.1) , fire dampers must meet UL 555 and be tested for closure under airflow and labeled for maximum airflow and direction (§ 606.2) , and ceiling radiation dampers must meet UL 555C or be tested as part of the floor/roof assembly per ASTM E119 or UL 263 (§ 606.3) . Combination fire/smoke dampers must comply with both UL 555 and UL 555S and the other requirements of § 606.1 and § 606.2 (§ 606.4) .
The single most important rule: install the listed damper type required by the Code at each protected penetration and follow the damper listing and the manufacturer's installation instructions exactly. See § 606.1–606.4.
Requirements in detail
Quick definitions (first mention bolded)
- Damper — valve or plate controlling airflow. § 206 (definitions) (CMC).
- Fire damper — closes on detection of heat to restrict flame. § 206 (definitions) (CMC).
- Smoke damper — arranged to automatically seal off airflow to restrict smoke. § 206 (definitions) (CMC).
- Ceiling radiation damper — listed device installed in the ceiling membrane to limit radiative heat transfer. § 206 (definitions) (CMC).
Decision table — which standard / requirement applies
| Damper type | Standard(s) / test method required | Key functional requirement(s) or value | Code Reference |
|---|---|---|---|
| Smoke damper | UL 555S | Installed per manufacturer; used where required by building code | § 606.1 |
| Fire damper | UL 555 | Tested for closure under airflow conditions; labeled for maximum airflow and direction of flow; duct connection per manufacturer | § 606.2 |
| Ceiling radiation damper | UL 555C OR tested as part of FRR assembly per ASTM E119 or UL 263 | Installed in the fire-resistive ceiling membrane; fire dampers that don't meet ceiling damper temperature limits may not substitute | § 606.3 |
| Combination fire/smoke damper | UL 555 AND UL 555S | Must satisfy smoke and fire damper rules referenced in § 606.1 and § 606.2 | § 606.4 |
| Periodic testing & inspection | NFPA 105 (smoke), NFPA 80 (fire), both for combination | Testing frequency & procedures per those NFPA standards | § 606.6 |
Notes: The table above summarizes the CMC mandates in § 606.1–606.4 (standards and installation direction). Additional rating values (e.g., minimum fire-damper hourly rating) and actuation temperature particulars are addressed in the California Building Code (see Related provisions) and testing sections of the CMC.
Installation and labeling requirements called out by the CMC
- Install all dampers in accordance with the manufacturer's installation instructions (repeated requirement in § 606.1–606.3) .
- Fire dampers must be labeled for both maximum airflow permitted and direction of flow and tested for closure under airflow (§ 606.2) .
- Ceiling radiation dampers must be installed in the fire-resistive ceiling membrane and fire dampers cannot be substituted if they don’t meet the ceiling damper temperature limitation (§ 606.3) .
- Combination dampers must meet the requirements for both fire and smoke dampers (§ 606.4) .
Exceptions & special cases
- Automatic activation of a smoke damper or combination smoke-fire damper requires the HVAC system serving those dampers to immediately shut down; exceptions exist where the HVAC system is part of an engineered smoke evacuation system, where the automatic activation closes all dampers in an enclosed space that must be protected, or where analysis shows shutoff would create greater hazard. The HVAC must remain off until dampers are reset and fully opened (§ 606.4.1) .
- Fire dampers are permitted only where required by the building code; ceiling radiation dampers may be substituted only if listed or if the assembly testing permits omission — fire dampers that do not meet the ceiling radiation damper temperature limit shall not be used as substitutes (§ 606.3) .
- Where multiple dampers are used in a single air path because of size, each damper must be listed for multiple arrangements and installed per the manufacturer (§ 606.7) .
- Access & identification: fire and smoke dampers must have approved access for inspection without tools, and access points must be identified with durable labels (e.g., “Smoke Damper”, “Fire Damper”, “Fire/Smoke Damper”) (§ 606.8) .
If you need code-specific exceptions that affect a particular occupancy or assembly (for example, special Office of the State Fire Marshal [SFM] rules, corridor vs. smoke-barrier locations), those are primarily in the California Building Code (related provisions) and should be consulted in parallel. Relevant CBC provisions cover rating values, actuation temperatures and where dampers are required.
Common mistakes
- Using a fire damper in place of a ceiling radiation damper when the fire damper does not meet the temperature limitation — prohibited by § 606.3.
- Installing a damper but not following the manufacturer's installation instructions or listing — the CMC repeatedly requires installation per the listing/manufacturer (all of § 606.1–606.4).
- Failing to ensure fire dampers are labeled for maximum airflow and direction or failing to use dampers listed for use in multiple arrangements when multiple units are required (§ 606.2, § 606.7).
- Not shutting down the HVAC when a smoke damper automatic activation occurs (unless an exception applies) — required by § 606.4.1.
- Forgetting access/labeling requirements for maintenance — see § 606.8.
Worked example — concrete scenario with numbers
Scenario: A metal duct penetrates a 2‑hour fire-resistance-rated floor/ceiling assembly and the design requires a damper at the ceiling line.
- Which damper is required? The CMC requires ceiling radiation dampers for ducts that penetrate the ceiling membrane of fire-resistance-rated floor/ceiling assemblies where required by the building code, and those dampers must comply with UL 555C or be tested as part of the assembly per ASTM E119 or UL 263 (§ 606.3) .
- Can a fire damper be used instead? Only if the fire damper meets the ceiling radiation damper’s temperature limitation. The CMC explicitly states that fire dampers not meeting the temperature limitation of ceiling radiation dampers shall not be used as a substitute (§ 606.3) . If the fire damper listing does not include the ceiling-radiation temperature limit, you must use a listed UL 555C ceiling radiation damper.
- Testing/labeling: make sure the ceiling radiation damper is listed and installed per the listing and manufacturer’s instructions. Also plan periodic testing/inspection per NFPA standards referenced by the CMC (smoke damper testing — NFPA 105; fire dampers — NFPA 80) (§ 606.6) .
- If the damper is a combination fire/smoke damper, it must meet UL 555 and UL 555S and the CMC sections for both types (§ 606.4) .
Note: the minimum hourly fire-damper rating for penetrations is provided in the California Building Code (Table 717.3.2.1) and must be checked for the exact penetration type; the CMC requires the proper listed device but the CBC gives the numerical fire-rating table. Consult CBC § 717.3.2.1 for the numeric minimums.
Related provisions (CMC sections)
- § 606.5 — Corridor Dampers (combination fire/smoke rules).
- § 606.6 — Periodic Testing and Inspection (references NFPA 80 and NFPA 105).
- § 606.7 — Multiple Arrangements (listing for multiple damper arrangements).
- § 606.8 — Access and Identification (access openings and labeling).
- § 606.9 — Freedom from Interference (installation to ensure positive operation).
- § 606.10 — Temperature Classification of Operating Elements (refer to building code for classification).
- § 607.1 — General requirements for ventilating ceilings (touches on ceiling assemblies).
If your project involves where dampers are required (for example, fire barriers, smoke barriers, corridor penetrations, shaft enclosures, or horizontal assemblies), consult the California Building Code sections (notably Chapter 7 — Section 717) for the locations, ratings, actuation temperatures and more detailed numeric values. The CBC provides the tables and actuation-temperature details referenced by the CMC.
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 606.2 High relevance — show source text
606.2 Fire Dampers. Fire dampers shall comply with UL 555, and shall be installed in accordance with the manufacturer’s installation instructions where required by the building code. Fire dampers shall have been tested for closure under airflow conditions and shall be labeled for both maximum airflow permitted and direction of flow. Where more than one damper is installed at a point in a single air path, the entire airflow shall be assumed to be passing through the smallest damper area.
Ductwork shall be connected to damper sleeves or assemblies in accordance with the fire damper manufacturer’s installation instructions.
606.3 Ceiling Radiation Dampers. Ceiling radiation dampers shall comply with UL 555C or shall be tested as part of a fire-resistance-rated floor-ceiling or roof-ceiling assembly in accordance with ASTM E119 or UL 263, and shall be installed in accordance with the manufacturer’s installation instructions in the fire-resistive ceiling membrane of floorceiling and roof-ceiling assemblies where required by the building code. Fire dampers not meeting the temperature limitation of ceiling radiation dampers shall not be used as a substitute.
606.4 Combination Fire/Smoke Dampers. Combination fire/smoke dampers shall comply with UL 555 and UL 555S and the requirements in Section 606.1 and Section 606.2.
606.4.1 When the automatic activation of a smoke damper or a combination smoke-fire damper occurs, the HVAC system serving such dampers shall immediately shut down.
Exceptions:
(1) HVAC systems that are part of an engineered smoke evacuation system.
(2) Where the automatic activation causes all the smoke dampers and combination smoke-fire dampers to close in the enclosed space having a common atmos- phere where openings are required to be protected.
(3) Where analysis demonstrates shutoff would create a greater hazard.
The HVAC system shall not be restarted again until all the dampers are reset and fully opened. 606.5 Corridor Dampers. Corridor dampers shall comply with the requirements of combination fire/smoke dampers in Section 606.4.
606.6 Periodic Testing and Inspection. Testing and inspection of dampers shall be in accordance with the following:
(1) Smoke dampers shall be tested in accordance with NFPA 105.
(2) Fire dampers shall be tested in accordance with NFPA 80.
(3) Combination fire/smoke dampers shall be tested in accordance with NFPA 80 and NFPA 105.
606.7 Multiple Arrangements. Where size requires the use of multiple dampers, each damper shall be listed for use in multiple arrangements and installed in accordance with the manufacturer’s installation instructions.
606.8 Access and Identification. Fire and smoke
dampers shall be provided with an approved means of access large enough to allow inspection and maintenance of the damper and its operating parts. The access shall not affect the integrity of the fire-resistance-rated assembly. The access openings shall not reduce the fire-resistance rating of the assembly.
Access shall not require the use of tools. Access doors in ducts shall be tight fitting and approved for the required duct construction. Access points shall be permanently identified on the exterior by a label with letters not less than [1] ⁄ 2 of an inch (12.7 mm) in height reading as one of the following:
(1) Smoke Damper
(2) Fire Damper
CMC § 605.2 High relevance — show source text
605.2 [OSHPD 1, 3 (Surgical Clinics), 4 & 5] Thermal acoustical lining materials shall not be installed within ducts, terminal boxes, sound traps, and other in-duct systems serving areas such as operating, cesarean operating rooms, delivery rooms, class 3 imaging, hybrid operating rooms, post anesthe- sia care units, cystoscopy, cardiac catheterization labs, nurs- eries, intensive care units, newborn intensive care units, protective environment rooms and airborne infection isolation rooms unless filters with 90 percent average efficiency based on ASHRAE Standard 52.2 or minimum efficiency rating value (MERV) of 14 are installed downstream of the duct lining. See ASHRAE 170, Section 6.9 for duct lining for non-sensitive
areas or rooms.
605.3 [OSHPD 1, 2, 4 & 5] Thermal or acoustical lining materials shall not be installed within ducts which are down- stream of the 99.97 percent high-efficiency particulate air (HEPA) filter required in Section 408.2.1 for protective envi-
ronment rooms.
2025 CALIFORNIA MECHANICAL CODE 141
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DUCT SYSTEMS
606.0 Smoke Dampers, Fire Dampers, and Ceiling Dampers.
606.1 Smoke Dampers. Smoke dampers shall comply with UL 555S, and shall be installed in accordance with the manufacturer’s installation instructions where required by the California Building Code or California Residential Code .
606.2 Fire Dampers. Fire dampers shall comply with UL 555, and shall be installed in accordance with the manufacturer’s installation instructions where required by the building code. Fire dampers shall have been tested for closure under airflow conditions and shall be labeled for both maximum airflow permitted and direction of flow. Where more than one damper is installed at a point in a single air path, the entire airflow shall be assumed to be passing through the smallest damper area.
Ductwork shall be connected to damper sleeves or assemblies in accordance with the fire damper manufacturer’s installation instructions.
606.3 Ceiling Radiation Dampers. Ceiling radiation dampers shall comply with UL 555C or shall be tested as part of a fire-resistance-rated floor-ceiling or roof-ceiling assembly in accordance with ASTM E119 or UL 263, and shall be installed in accordance with the manufacturer’s installation instructions in the fire-resistive ceiling membrane of floorceiling and roof-ceiling assemblies where required by the building code. Fire dampers not meeting the temperature limitation of ceiling radiation dampers shall not be used as a substitute.
606.4 Combination Fire/Smoke Dampers. Combination fire/smoke dampers shall comply with UL 555 and UL 555S and the requirements in Section 606.1 and Section 606.2.
606.4.1 When the automatic activation of a smoke damper or a combination smoke-fire damper occurs, the HVAC system serving such dampers shall immediately shut down.
Exceptions:
(1) HVAC systems that are part of an engineered smoke evacuation system.
CMC § 717.1.1 High relevance — show source text
717.1.1 Ducts and air transfer openings. Ducts transitioning horizontally between shafts shall not require a shaft enclosure provided that the duct penetration into each associated shaft is protected with dampers complying with this section.
717.1.2 Ducts that penetrate fire-resistance-rated assemblies without dampers. Ducts that penetrate fire-resistance-rated walls and are not required by this section to have fire dampers shall comply with the requirements of Sections 714.3 through 714.4.3. Ducts that penetrate horizontal assemblies not required to be contained within a shaft and not required by this section to have fire dampers shall comply with the requirements of Sections 714.5 through 714.6.2.
717.1.2.1 Ducts that penetrate nonfire-resistance-rated assemblies. The space around a duct penetrating a nonfire-resistance-rated floor assembly shall comply with Section 717.6.3.
717.2 Installation. Fire dampers, smoke dampers, combination fire/smoke dampers and ceiling radiation dampers located within air distribution and smoke control systems shall be installed in accordance with the manufacturer’s instructions, the dampers’ listing and Sections 717.2.1 through 717.2.4.
717.2.1 Smoke control system. Where the installation of a fire damper will interfere with the operation of a required smoke control system in accordance with Section 909, approved alternative protection shall be utilized. Where mechanical systems including ducts and dampers utilized for normal building ventilation serve as part of the smoke control system, the expected performance of these systems in smoke control mode shall be addressed in the rational analysis required by Section 909.4.
717.2.2 Hazardous exhaust ducts. Fire dampers for hazardous exhaust duct systems shall comply with the California Mechanical Code .
717.2.3 Static dampers. Fire dampers and ceiling radiation dampers that are listed for use in static systems shall only be installed in heating, ventilation and air-conditioning systems that are automatically shut down in the event of a fire.
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717.2.4 Mechanical, electrical and plumbing controls. Mechanical, electrical and plumbing controls shall not be installed in air duct systems.
Exception: Controls where the wiring is directly associated with the air distribution system. The wiring shall comply with the requirements of Section 601 of the California Mechanical Code and be as short as practicable.
717.2.4.1 Controls not permitted to be installed through dampers. Mechanical, electrical and plumbing controls shall not be installed through fire dampers, smoke dampers, combination fire/smoke dampers or ceiling radiation dampers unless otherwise permitted by the manufacturer and the listing.
717.3 Damper testing, ratings and actuation. Damper testing, ratings and actuation shall be in accordance with Sections 717.3.1 through 717.3.3.
717.3.1 Damper testing. Dampers shall be listed and labeled in accordance with the standards in this section.
- Fire dampers shall comply with the requirements of UL 555.
- Smoke dampers shall comply with the requirements of UL 555S.
- Combination fire/smoke dampers shall comply with the requirements of both UL 555 and UL 555S.
CMC § 717.2.3 High relevance — show source text
717.2.3 Static dampers. Fire dampers and ceiling radiation dampers that are listed for use in static systems shall only be installed in heating, ventilation and air-conditioning systems that are automatically shut down in the event of a fire.
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717.2.4 Mechanical, electrical and plumbing controls. Mechanical, electrical and plumbing controls shall not be installed in air duct systems.
Exception: Controls where the wiring is directly associated with the air distribution system. The wiring shall comply with the requirements of Section 601 of the California Mechanical Code and be as short as practicable.
717.2.4.1 Controls not permitted to be installed through dampers. Mechanical, electrical and plumbing controls shall not be installed through fire dampers, smoke dampers, combination fire/smoke dampers or ceiling radiation dampers unless otherwise permitted by the manufacturer and the listing.
717.3 Damper testing, ratings and actuation. Damper testing, ratings and actuation shall be in accordance with Sections 717.3.1 through 717.3.3.
717.3.1 Damper testing. Dampers shall be listed and labeled in accordance with the standards in this section.
- Fire dampers shall comply with the requirements of UL 555.
- Smoke dampers shall comply with the requirements of UL 555S.
- Combination fire/smoke dampers shall comply with the requirements of both UL 555 and UL 555S.
- Ceiling radiation dampers shall comply with the requirements of UL 555C or shall be tested as part of a fire-resistancerated floor/ceiling or roof/ceiling assembly in accordance with ASTM E119 or UL 263.
- Corridor dampers shall comply with requirements of both UL 555 and UL 555S. Corridor dampers shall demonstrate acceptable closure performance when subjected to 150 feet per minute (0.76 mps) velocity across the face of the damper during the UL 555 fire exposure test.
717.3.2 Damper rating. Damper ratings shall be in accordance with Sections 717.3.2.1 through 717.3.2.4.
717.3.2.1 Fire damper ratings. Fire dampers shall have the minimum rating specified in Table 717.3.2.1.
TABLE 717.3.2.1—FIRE DAMPER RATING Col2 TYPE OF PENETRATION MINIMUM DAMPER RATING (hours) Less than 3-hour fire-resistance-rated assemblies 1.5 3-hour or greater fire-resistance-rated assemblies 3 717.3.2.2 Smoke damper ratings. Smoke damper leakage ratings shall be Class I or II. Elevated temperature ratings shall be not less than 250°F (121°C).
717.3.2.3 Combination fire/smoke damper ratings. Combination fire/smoke dampers shall have the minimum rating specified for fire dampers in Table 717.3.2.1 and shall have the minimum rating specified for smoke dampers in Section 717.3.2.2.
CMC § 0.76 High relevance — show source text
Combination fire/smoke dampers shall comply with the requirements of both UL 555 and UL 555S. 4. Ceiling radiation dampers shall comply with the requirements of UL 555C or shall be tested as part of a fire-resistancerated floor/ceiling or roof/ceiling assembly in accordance with ASTM E119 or UL 263. 5. Corridor dampers shall comply with requirements of both UL 555 and UL 555S. Corridor dampers shall demonstrate acceptable closure performance when subjected to 150 feet per minute (0.76 mps) velocity across the face of the damper during the UL 555 fire exposure test.
717.3.2 Damper rating. Damper ratings shall be in accordance with Sections 717.3.2.1 through 717.3.2.4.
717.3.2.1 Fire damper ratings. Fire dampers shall have the minimum rating specified in Table 717.3.2.1.
TABLE 717.3.2.1—FIRE DAMPER RATING Col2 TYPE OF PENETRATION MINIMUM DAMPER RATING (hours) Less than 3-hour fire-resistance-rated assemblies 1.5 3-hour or greater fire-resistance-rated assemblies 3 717.3.2.2 Smoke damper ratings. Smoke damper leakage ratings shall be Class I or II. Elevated temperature ratings shall be not less than 250°F (121°C).
717.3.2.3 Combination fire/smoke damper ratings. Combination fire/smoke dampers shall have the minimum rating specified for fire dampers in Table 717.3.2.1 and shall have the minimum rating specified for smoke dampers in Section 717.3.2.2.
717.3.2.4 Corridor damper ratings. Corridor dampers shall have the following minimum ratings:
- One-hour fire-resistance rating.
- Class I or II leakage rating as specified in Section 717.3.2.2.
717.3.3 Damper actuation. Damper actuation shall be in accordance with Sections 717.3.3.1 through 717.3.3.5 as applicable.
717.3.3.1 Fire damper actuation. Primary heat responsive devices used to actuate fire dampers shall meet one of the following requirements:
- The operating temperature shall be approximately 50°F (10°C) above the normal temperature within the duct system, but not less than 160°F (71°C).
- The operating temperature shall be not more than 350°F (177°C) where located in a smoke control system complying with Section 909.
717.3.3.2 Smoke damper actuation. The smoke damper shall close upon actuation of a listed smoke detector or detectors installed in accordance with Section 907.3 and one of the following methods, as applicable:
- Where a smoke damper is installed within a duct, a smoke detector shall be installed inside the duct or outside the duct with sampling tubes protruding into the duct. The detector or tubes within the duct shall be within 5 feet (1524 mm) of the damper. Air outlets and inlets shall not be located between the detector or tubes and the damper. The detector shall be listed for the air velocity, temperature and humidity anticipated at the point where it is installed. Other than in mechanical smoke control systems, dampers shall be closed upon fan shutdown where local smoke detectors require a minimum velocity to operate.
CMC § 606.5 High relevance — show source text
(3) Where analysis demonstrates shutoff would create a greater hazard.
The HVAC system shall not be restarted again until all the dampers are reset and fully opened. 606.5 Corridor Dampers. Corridor dampers shall comply with the requirements of combination fire/smoke dampers in Section 606.4.
606.6 Periodic Testing and Inspection. Testing and inspection of dampers shall be in accordance with the following:
(1) Smoke dampers shall be tested in accordance with NFPA 105.
(2) Fire dampers shall be tested in accordance with NFPA 80.
(3) Combination fire/smoke dampers shall be tested in accordance with NFPA 80 and NFPA 105.
606.7 Multiple Arrangements. Where size requires the use of multiple dampers, each damper shall be listed for use in multiple arrangements and installed in accordance with the manufacturer’s installation instructions.
606.8 Access and Identification. Fire and smoke
dampers shall be provided with an approved means of access large enough to allow inspection and maintenance of the damper and its operating parts. The access shall not affect the integrity of the fire-resistance-rated assembly. The access openings shall not reduce the fire-resistance rating of the assembly.
Access shall not require the use of tools. Access doors in ducts shall be tight fitting and approved for the required duct construction. Access points shall be permanently identified on the exterior by a label with letters not less than [1] ⁄ 2 of an inch (12.7 mm) in height reading as one of the following:
(1) Smoke Damper
(2) Fire Damper
(3) Fire/Smoke Damper
606.9 Freedom from Interference. Dampers shall be installed in a manner to ensure positive closing or opening as required by function. Interior liners or insulation shall be held back from portions of a damper, its sleeve, or adjoining duct that would interfere with the damper’s proper operation. Exterior materials shall be installed so as to not interfere with the
operation or maintenance of external operating devices needed for the function of the damper.
606.10 Temperature Classification of Operating Ele- ments. Fusible links, thermal sensors, and pneumatic or electric operators shall have a temperature rating or classification as in accordance with the building code.
607.0 Ventilating Ceilings.
607.1 General. Perforated ceilings shall be permitted to be used for air supply within the limitations of this section. Exit corridors, where required to be of fire-resistive construction by the California Building Code, shall not have ventilating ceilings.
607.1.1 [OSHPD 1, 1R, 2, 3, 4 & 5] Ventilating ceil- ings are not permitted in health facilities.
607.2 Requirements. Ventilating ceilings shall comply with the following:
(1) Suspended ventilating ceiling material shall have a Class 1 flame spread classification on both sides, determined in accordance with the building code. Suspended ventilating ceiling supports shall be of noncombustible materials.
(2) Luminaires recessed into ventilating ceilings shall be of a type approved for that purpose.
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CMC § 717.3.2.4 High relevance — show source text
717.3.2.4 Corridor damper ratings. Corridor dampers shall have the following minimum ratings:
- One-hour fire-resistance rating.
- Class I or II leakage rating as specified in Section 717.3.2.2.
717.3.3 Damper actuation. Damper actuation shall be in accordance with Sections 717.3.3.1 through 717.3.3.5 as applicable.
717.3.3.1 Fire damper actuation. Primary heat responsive devices used to actuate fire dampers shall meet one of the following requirements:
- The operating temperature shall be approximately 50°F (10°C) above the normal temperature within the duct system, but not less than 160°F (71°C).
- The operating temperature shall be not more than 350°F (177°C) where located in a smoke control system complying with Section 909.
717.3.3.2 Smoke damper actuation. The smoke damper shall close upon actuation of a listed smoke detector or detectors installed in accordance with Section 907.3 and one of the following methods, as applicable:
- Where a smoke damper is installed within a duct, a smoke detector shall be installed inside the duct or outside the duct with sampling tubes protruding into the duct. The detector or tubes within the duct shall be within 5 feet (1524 mm) of the damper. Air outlets and inlets shall not be located between the detector or tubes and the damper. The detector shall be listed for the air velocity, temperature and humidity anticipated at the point where it is installed. Other than in mechanical smoke control systems, dampers shall be closed upon fan shutdown where local smoke detectors require a minimum velocity to operate.
- Where a smoke damper is installed above smoke barrier doors in a smoke barrier, a spot-type detector shall be installed on either side of the smoke barrier door opening. The detector shall be listed for releasing service if used for direct interface with the damper.
- Where a smoke damper is installed within an air transfer opening in a wall, a spot-type detector shall be installed within 5 feet (1524 mm) horizontally of the damper. The detector shall be listed for releasing service if used for direct interface with the damper.
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- Where a smoke damper is installed in a corridor wall or ceiling, the damper shall be permitted to be controlled by a smoke detection system installed in the corridor.
- Where a smoke detection system is installed in all areas served by the duct in which the damper will be located, the smoke dampers shall be permitted to be controlled by the smoke detection system.
717.3.3.3 Combination fire/smoke damper actuation. Combination fire/smoke damper actuation shall be in accordance with Sections 717.3.3.1 and 717.3.3.2. Combination fire/smoke dampers installed in smoke control system shaft penetrations shall not be activated by local area smoke detection unless it is secondary to the smoke control system controls.
717.3.3.4 Ceiling radiation damper actuation. The operating temperature of a ceiling radiation damper actuation device shall be 50°F (27.8°C) above the normal temperature within the duct system, but not less than 160°F (71°C).
CMC § 7-35 High relevance — show source text
- Where a smoke damper is installed above smoke barrier doors in a smoke barrier, a spot-type detector shall be installed on either side of the smoke barrier door opening. The detector shall be listed for releasing service if used for direct interface with the damper.
- Where a smoke damper is installed within an air transfer opening in a wall, a spot-type detector shall be installed within 5 feet (1524 mm) horizontally of the damper. The detector shall be listed for releasing service if used for direct interface with the damper.
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- Where a smoke damper is installed in a corridor wall or ceiling, the damper shall be permitted to be controlled by a smoke detection system installed in the corridor.
- Where a smoke detection system is installed in all areas served by the duct in which the damper will be located, the smoke dampers shall be permitted to be controlled by the smoke detection system.
717.3.3.3 Combination fire/smoke damper actuation. Combination fire/smoke damper actuation shall be in accordance with Sections 717.3.3.1 and 717.3.3.2. Combination fire/smoke dampers installed in smoke control system shaft penetrations shall not be activated by local area smoke detection unless it is secondary to the smoke control system controls.
717.3.3.4 Ceiling radiation damper actuation. The operating temperature of a ceiling radiation damper actuation device shall be 50°F (27.8°C) above the normal temperature within the duct system, but not less than 160°F (71°C).
717.3.3.5 Corridor damper actuation. Corridor damper actuation shall be in accordance with Sections 717.3.3.1 and 717.3.3.2.
717.4 Access and identification. Access and identification of fire and smoke dampers shall comply with Sections 717.4.1 through 717.4.2.
717.4.1 Access. Fire and smoke dampers shall be provided with an approved means of access that is large enough to permit inspection and maintenance of the damper and its operating parts. Dampers equipped with fusible links, internal operators, or both shall be provided with an access door that is not less than 12 inches (305 mm) square or provided with a removable duct section.
717.4.1.1 Access openings. The access shall not affect the integrity of fire-resistance-rated assemblies. The access openings shall not reduce the fire-resistance rating of the assembly. Access doors in ducts shall be tight fitting and suitable for the required duct construction.
717.4.1.2 Restricted access. Where space constraints or physical barriers restrict access to a damper for periodic inspection and testing, the damper shall be a single- or multi-blade type damper and shall comply with the remote inspection requirements of NFPA 80 or NFPA 105.
717.4.2 Identification. Access points shall be permanently identified on the exterior by a label having letters not less than [1] / 2 inch (12.7 mm) in height reading: “FIRE/SMOKE DAMPER,” “SMOKE DAMPER” or “FIRE DAMPER.”
CMC § 714.5.2 High relevance — show source text
A shaft enclosure in accordance with Section 713.
A listed ceiling radiation damper installed at the ceiling line where a duct penetrates the ceiling of a fire-resistance-rated floor/ceiling or roof/ceiling assembly. Exceptions:
A fire-resistance-rated assembly tested in accordance with ASTM E119 or UL 263 showing that ceiling radiation dampers are not required in order to maintain the fire-resistance rating of the assembly.
Where exhaust duct or outdoor air duct penetrations protected in accordance with Section 714.5.2 are located within the cavity of a wall and do not pass through another dwelling unit or tenant space.
Where duct and air transfer openings are protected with a duct outlet penetration system tested as part of a fire-resistance-rated assembly in accordance with ASTM E119 or UL 263.
A listed ceiling radiation damper installed at the ceiling line where a diffuser with no duct attached penetrates the ceiling of a fire-resistance-rated floor/ceiling or roof/ceiling assembly. Exceptions:
A fire-resistance-rated assembly tested in accordance with ASTM E119 or UL 263 showing that ceiling radiation dampers are not required in order to maintain the fire-resistance rating of the assembly.
Where duct and air transfer openings are protected with a duct outlet penetration system tested as part of a fire-resistance-rated assembly in accordance with ASTM E119 or UL 263.
717.6.2.1 Ceiling radiation dampers testing and installation. Ceiling radiation dampers shall be tested in accordance with Section 717.3.1. Ceiling radiation dampers shall be installed in accordance with the details specified in the fire-resistance-rated assembly and the manufacturer’s instructions and the listing.
717.6.2.1.1 Dynamic systems. Only ceiling radiation dampers labeled for use in dynamic systems shall be installed in heating, ventilation and air-conditioning systems designed to operate with fans on during a fire.
717.6.2.1.2 Static systems. Static ceiling radiation dampers shall be provided with systems that are not designed to operate during a fire.
Exceptions:
- Where a static ceiling radiation damper is installed at the opening of a duct, a smoke detector shall be installed inside the duct or outside the duct with sampling tubes protruding into the duct. The detector or tubes in the duct shall be within 5 feet (1524 mm) of the damper. Air outlets and inlets shall not be located between the detector or tubes and the damper. The detector shall be listed for the air velocity, temperature and humidity
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anticipated at the point where it is installed. Other than in mechanical smoke control systems, dampers shall be closed upon fan shutdown where local smoke detectors require a minimum velocity to operate. 2. Where a static ceiling radiation damper is installed in a ceiling, the ceiling radiation damper shall be permitted to be controlled by a smoke detection system installed in the same room or area as the ceiling radiation damper. 3. A static ceiling radiation damper shall be permitted to be installed in a room where an occupant sensor is provided within the room that will shut down the system.
717.6.3 Nonfire-resistance-rated floor assemblies. Duct systems constructed of approved materials in accordance with the California Mechanical Code that penetrate nonfire-resistance-rated floor assemblies shall be protected by any of the following methods:
CMC § 0.0187 High relevance — show source text
Exception: In occupancies other than Groups I-2 and I-3, a duct is permitted to penetrate three floors or less without a fire damper at each floor, provided that such duct meets all of the following requirements:
- The duct shall be contained and located within the cavity of a wall and shall be constructed of steel having a minimum wall thickness of 0.0187 inches (0.4712 mm) (No. 26 gage).
- The duct shall open into only one dwelling unit or sleeping unit and the duct system shall be continuous from the unit to the exterior of the building.
- The duct shall not exceed 4-inch (102 mm) nominal diameter and the total area of such ducts shall not exceed 100 square inches (0.065 m [2] ) in any 100 square feet (9.3 m [2] ) of floor area.
- The annular space around the duct is protected with materials that prevent the passage of flame and hot gases sufficient to ignite cotton waste where subjected to ASTM E119 or UL 263 time-temperature conditions under a minimum positive pressure differential of 0.01 inch of water (2.49 Pa) at the location of the penetration for the time period equivalent to the fire-resistance rating of the construction penetrated.
- Grille openings located in a ceiling of a fire-resistance-rated floor/ceiling or roof/ceiling assembly shall be protected with a listed ceiling radiation damper installed in accordance with Section 717.6.2.1.
717.6.2 Membrane penetrations. Ducts and air transfer openings constructed of approved materials in accordance with the Cali- fornia Mechanical Code that penetrate the ceiling membrane of a fire-resistance-rated floor/ceiling or roof/ceiling assembly shall be protected with one of the following:
A shaft enclosure in accordance with Section 713.
A listed ceiling radiation damper installed at the ceiling line where a duct penetrates the ceiling of a fire-resistance-rated floor/ceiling or roof/ceiling assembly. Exceptions:
A fire-resistance-rated assembly tested in accordance with ASTM E119 or UL 263 showing that ceiling radiation dampers are not required in order to maintain the fire-resistance rating of the assembly.
Where exhaust duct or outdoor air duct penetrations protected in accordance with Section 714.5.2 are located within the cavity of a wall and do not pass through another dwelling unit or tenant space.
Where duct and air transfer openings are protected with a duct outlet penetration system tested as part of a fire-resistance-rated assembly in accordance with ASTM E119 or UL 263.
A listed ceiling radiation damper installed at the ceiling line where a diffuser with no duct attached penetrates the ceiling of a fire-resistance-rated floor/ceiling or roof/ceiling assembly. Exceptions:
A fire-resistance-rated assembly tested in accordance with ASTM E119 or UL 263 showing that ceiling radiation dampers are not required in order to maintain the fire-resistance rating of the assembly.
Where duct and air transfer openings are protected with a duct outlet penetration system tested as part of a fire-resistance-rated assembly in accordance with ASTM E119 or UL 263.
717.6.2.1 Ceiling radiation dampers testing and installation. Ceiling radiation dampers shall be tested in accordance with Section 717.3.1. Ceiling radiation dampers shall be installed in accordance with the details specified in the fire-resistance-rated assembly and the manufacturer’s instructions and the listing.
CMC § 3.3.15 High relevance — show source text
[NFPA 96:3.3.15] For the purpose of the definition, it specifically includes the exhaust compartment of hoods and welded joints of exhaust ducts, yet specifically does not include filter support frames or appendages inside hoods.
Conversion Burner, Gas. A unit consisting of a burner and its controls utilizing gaseous fuel for installation in an appliance originally utilizing another fuel. [NFPA 54:3.3.16.2]
Cooling. Air cooling to provide a room or space temperature of 68°F (20°C) or above.
Cooling System. All of the equipment, ducts and components, including associated refrigeration, intended or installed for the purpose of cooling air by mechanical means and discharging such air into any room or conditioned space. This definition shall not include an evaporative cooler.
Cooling Unit. A self-contained refrigeration system that has been factory assembled tested, and installed with or without conditioned air and ducts, without connecting any refrigerant-containing parts. This definition shall not include a portable cooling unit or an absorption unit.
Copper Alloy. A homogenous mixture of two or more metals in which copper is the primary component, such as brass and bronze.
Crawl Space. In a building, an area accessible by crawling, having a clearance less than human height, for access to plumbing or wiring, storage, etc.
CSST. An acronym for corrugated stainless steel tubing.
2025 CALIFORNIA MECHANICAL CODE 35
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DEFINITIONS
206.0 – D –
Damper. A valve or plate for controlling draft or the flow of gases, including air. [NFPA 211:3.3.52]
Ceiling Radiation Damper. A listed device installed in a ceiling membrane of a fire-resistance-rated floorceiling or roof-ceiling assembly to automatically limit the radiative heat transfer through an air inlet/outlet opening. [NFPA 5000:3.3.140.1]
Combination Fire/Smoke Damper. An automaticclosing metal assembly consisting of one or more louvers, blades, slats, or vanes that closes upon detection of heat or smoke as to restrict the passage of flame and smoke.
Corridor Damper. An automatic closing metal assembly consisting of one or more louvers, blades, slats, or vanes that closes upon detection of heat or smoke as to restrict the passage of flame and smoke used where air ducts penetrate horizontal openings in fire-resistancerated corridors.
Fire Damper. An automatic-closing metal assembly consisting of one or more louvers, blades, slats, or vanes that closes upon detection of heat so as to restrict the passage of flame.
Smoke Damper. A damper arranged to seal off airflow automatically through a part of an air duct system so as to restrict the passage of smoke.
Volume Damper. A device that, when installed, will restrict, retard, or direct the flow of air in any duct, or the products of combustion in any heat-producing equipment, its vent connector, vent, or chimney.
Department. [HCD 1 & HCD 2] “Department” means the Department of Housing and Community Development.
CMC § 717.5.6 High relevance — show source text
Exception: Smoke dampers are not required where the openings in ducts are limited to a single smoke compartment and the ducts are constructed of steel. � 717.5.6 Exterior walls. Ducts and air transfer openings in fire-resistance-rated exterior walls required to have protected openings in accordance with Section 705.11 shall be protected with listed fire dampers installed in accordance with their listing.
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717.5.7 Smoke partitions. A listed smoke damper designed to resist the passage of smoke shall be provided at each point that an air transfer opening penetrates a smoke partition. Smoke dampers and smoke damper actuation methods shall comply with Section 717.3.3.2.
Exception: Where the installation of a smoke damper will interfere with the operation of a required smoke control system in accordance with Section 909, approved alternative protection shall be utilized.
717.6 Horizontal assemblies. Penetrations by ducts and air transfer openings of a floor, floor/ceiling assembly or the ceiling membrane of a roof/ceiling assembly shall be protected by a shaft enclosure that complies with Section 713 or shall comply with Sections 717.6.1 through 717.6.3.
717.6.1 Through penetrations. A duct constructed of approved materials in accordance with the California Mechanical Code that penetrates a fire-resistance-rated floor/ceiling assembly that connects not more than two stories is permitted without shaft enclosure protection, provided that a listed fire damper is installed at the floor line or the duct is protected in accordance with Section 714.5. For air transfer openings, see Section 712.1.9.
Exception: In occupancies other than Groups I-2 and I-3, a duct is permitted to penetrate three floors or less without a fire damper at each floor, provided that such duct meets all of the following requirements:
- The duct shall be contained and located within the cavity of a wall and shall be constructed of steel having a minimum wall thickness of 0.0187 inches (0.4712 mm) (No. 26 gage).
- The duct shall open into only one dwelling unit or sleeping unit and the duct system shall be continuous from the unit to the exterior of the building.
- The duct shall not exceed 4-inch (102 mm) nominal diameter and the total area of such ducts shall not exceed 100 square inches (0.065 m [2] ) in any 100 square feet (9.3 m [2] ) of floor area.
- The annular space around the duct is protected with materials that prevent the passage of flame and hot gases sufficient to ignite cotton waste where subjected to ASTM E119 or UL 263 time-temperature conditions under a minimum positive pressure differential of 0.01 inch of water (2.49 Pa) at the location of the penetration for the time period equivalent to the fire-resistance rating of the construction penetrated.
- Grille openings located in a ceiling of a fire-resistance-rated floor/ceiling or roof/ceiling assembly shall be protected with a listed ceiling radiation damper installed in accordance with Section 717.6.2.1.
Frequently asked questions
When does the CMC require a smoke damper?
When the California Building Code requires it (for example, at air-transfer openings that penetrate smoke barriers or similar conditions); the CMC requires smoke dampers to comply with UL 555S and to be installed per the manufacturer (§ 606.1) .
Are fire dampers required to be labeled for airflow?
Yes — fire dampers must be labeled for both maximum airflow permitted and direction of flow and must have been tested for closure under airflow conditions (§ 606.2) .
Can a fire damper substitute for a ceiling radiation damper?
Not unless the fire damper meets the temperature limitation required for ceiling radiation dampers — the CMC explicitly prohibits substituting fire dampers that do not meet that limit (§ 606.3) .
What happens to the HVAC when a smoke damper automatically activates?
The HVAC system serving such dampers shall immediately shut down, except for limited exceptions (engineered smoke evacuation systems, simultaneous closure in enclosed protected spaces, or where analysis shows shutoff is more hazardous) (§ 606.4.1) .
Where are testing procedures required by the CMC found?
Periodic testing and inspection are required per § 606.6: smoke dampers — NFPA 105; fire dampers — NFPA 80; combination dampers — both NFPA 80 and NFPA 105.
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