Appeal 33419

2022 OSSC 602.4.2.5 Concealed spaces and 2022 OMSC 602.2.1 Materials within plenums

OSSC 602.4.2.5 states that concealed spaces in type IVB construction shall not contain combustibles other than electrical, mechanical, fire protection, or plumbing materials and equipment permitted in plenums in accordance with Section 602 of the Mechanical Code, and shall comply with all applicable provisions of Section 718. Combustible construction forming concealed spaces shall be protected in accordance with Section 602.4.1.2.

OMSC602.2.1 states that except as required by Sections 602.2.1.1 through 6.2.2.1.8, materials within plenums shall be noncombustible or shall be listed and labeled as having a flame spread index of not more than 25 and a smoke-developed index of not more than 50 when tested in accordance with ASTM E84 or UL 723. The exceptions include the following:

1. Rigid and flexible ducts and connectors shall conform to Section 603.
2. Duct coverings, linings, tape and connectors shall conform to Section 603 and 604.
3. This section shall not apply to materials exposed within plenums in one- and two- family dwellings.
4. This section shall not apply to smoke detectors.
5. Combustible materials enclosed within one of the following:

5.1. Continuous non-combustible raceways or enclosures.
5.2. Approved gypsum board assemblies.
5.3. Materials listed and labelled for installation within a plenum and listed for the application.

1. Materials in Group H, Division 5 fabrication areas and the areas above and below the fabrication area that share a common air recirculation path with the fabrication area.

The goal of this appeal is to clarify the intent of the OSSC and OMSC regarding type IVB buildings and concealed spaces and plenums and allow combustible MEP items to be in approved gypsum board assemblies and walls packed with non-combustible materials as is written in the mechanical code that is referenced.

ORIGINAL TEXT

The permitted type IVB building has mechanical, electrical and plumbing materials located in plenums and walls throughout the building. This appeal proposes that the intent of the OSSC and OMSC sections referenced should allow combustible MEP items in the following two locations based on the listed exceptions.

1. Combustible MEP materials within rated wall or ceiling assemblies.
2. Combustible MEP materials within non-rated wall assemblies that are packed with non-combustible insulation such as fiberglass and mineral wool.

RECONSIDERATION TEXT

The permitted type IVB building has mechanical, electrical and plumbing materials located in plenums and walls throughout the building. This appeal proposes that the intent of the OSSC and OMSC sections referenced allow for combustible MEP items in the below bullet pointed conditions, based on the associated listed exceptions in OMSC 602.2.1.

• Combustible MEP materials within rated wall or ceiling assemblies (exception 5.2)
• Combustible MEP materials within non-rated wall assemblies that are fully packed with non-combustible mineral wool insulation (exception 5.3)

The design includes firestopping at all MEP penetrations through rated floors, requiring tested firestopping systems with an F and T rating to match the assembly. Firestopping is also required at all penetrations through rated walls. At all other concealed locations, MEP materials will prescriptively meet the requirements of OMSC 602 as is referenced in OSSC 602.4.2.5, or be protected by an insulating wrap specific to the material and rated for use in plenums per exception 5.3.

ORIGINAL TEXT

OMSC 602.2.1, exception 5.2 states that combustible MEP materials within ‘approved gypsum board assemblies’ do not have to be tested in accordance with ASTM E84 or UL 723. A fire rated wall or ceiling assembly encases all MEP materials within type X rated gypsum board and is fully taped and sealed to prevent the passage of fire. All penetrations through vertical and horizontal assemblies are sealed for fire according to OSSC 714. We feel that this type of fire rated assembly meets the intent of the code as an approved gypsum board assembly.

OMSC 602.2.1, exception 5.3 states that combustible MEP materials that are fully enclosed within materials that are listed and labeled for installation within a plenum and listed for the application are acceptable. MEP materials within non-rated walls are protected on all sides by either a) a wall fully packed with noncombustible insulation or b) are MEP materials that occur within a single stud cavity packed with noncombustible insulation. All floor penetrations entering or exiting the wall cavity are fully sealed for passage of fire according to OSSC 714. We feel that this noncombustible insulation protection meets the intent of the code as fully enclosing combustible MEP materials.

RECONSIDERATION TEXT

OSSC 602.4.2.5, as prescriptively written, requires that OMSC 602.2.1 be referenced for all concealed spaces (not just plenums as the OMSC section describes) in type IVB construction. This mechanical code section requires that MEP materials be either noncombustible or meet the requirements of ASTM E84 or UL 723, unless provisions of the listed exceptions are met. Exception 5.2 states that combustible MEP materials within approved gypsum board assemblies do not have to be tested in accordance with ASTM E84 or UL 723. Exception 5.3 states that combustible MEP materials that are fully enclosed within materials that are listed and labeled for installation within a plenum and listed for the application are acceptable. The mechanical code commentary further supports this interpretation, stating that “Exception 5 recognizes the practice of enclosing combustible materials, such as plastic piping, in gypsum board assemblies or in insulation materials that are listed and labelled for this specific application.” Within the permitted documents, wall and ceiling assemblies, both rated and unrated, encase combustible MEP materials. Where UL listed, fire rated walls occur in this project, they encase MEP materials within type X rated gypsum board that is fully taped and sealed to prevent the passage of fire. Per the written exceptions and further explanation in the code commentary, we can interpret that UL listed, fire rated assemblies are the definition of ‘approved gypsum board assemblies.’ All penetrations through UL listed, fire rated, vertical assemblies are sealed for fire according to OSSC 714. All horizontal penetrations are sealed for fire per OSSC 714. Where unrated walls occur in this project, combustible MEP materials are fully encased in mineral wool batt insulation, a plenum rated insulation material. All mass timber elements within unrated concealed areas are fully covered by 80 minutes of type X gypsum board.

The included drawing exhibits illustrate the fire ratings of all assemblies within the building and indicate firestopping at all MEP penetrations. 2-hour rated floor/ceiling assemblies (Reference A0.14) state that all mass timber elements exposed within a concealed space are covered by 80 minutes of type X gypsum board, as is required by OSSC 602.4.1.2. Where UL listed, fire rated demising walls (Reference A0.11) intersect with 2-hour rated horizontal assemblies, the underside of mass timber elements are covered by a minimum of 80 minutes of type x gypsum board (Reference A0.16), and walls are packed with fiberglass batt insulation to meet acoustic ratings and provide coverage of mass timber elements at the floor. Where unrated partition walls intersect with 2-hour rated horizontal assemblies, those containing combustible MEP items will be packed with mineral wool insulation (Reference A0.11). All MEP penetrations that occur through 2-hour rated floors are firestopped to prevent the passage of fire and smoke to other floors. Firestopping systems must be listed for use with the specified material and have F and T ratings equivalent to the rated assembly.

We feel that this level of protection of mass timber elements, while isolating passage of fire and smoke between floors and protecting individual combustible MEP items with either mineral wool insulation or rated gypsum board assemblies, meets the intent of the code as it is written. In addition to our supporting drawings, a stamped letter from a licensed fire protection engineer is included to support this appeal.