FIRE RATING

The following information is intended as a general overview of Fire Rating for suspended wood ceilings. The final authoritative voice on this subject should be the codes that apply to your project, community, and product data sheets. The fire retardant products utilized by 9Wood are reviewed briefly.

1.0 CURRENT CODE

The International Code Council (ICC) was established in 1994 as a nonprofit organization dedicated to developing a single set of comprehensive and coordinated national model construction codes. The founders of the ICC are Building Officials and Code Administrators International, Inc. (BOCA), International Conference of Building Officials (ICBO), and Southern Building Code Congress International, Inc. (SBCCI). Since the early part of the last century, these nonprofit organizations developed the three separate sets of model codes used throughout the United States. When the time came for a single set of codes, the nation's three model code groups responded by creating the International Code Council and by developing codes without regional limitations.

The most critical sections of the new IBC (Int'l Building Code) relating to fire ratings are:

• Use or Occupancy Classification
• Special Use or Occupancy Requirements
• Types of Construction
• Fire Resistant Materials and Construction
• Interior Finishes
• Fire Protection Systems
• Means of Egress
• Accessibility

The most significant of these include IBC & IFC Section 8: Interiors, IBC Section 4: Special Occupancies, and NFPA 13: Sprinklers---Concealed Spaces. IMC Section 6: Ducts and Plenums apply for Return Air Plenums. The building occupancy group as well as local codes and fire marshal interpretations of those codes give final consideration.

1.1 CODE SECTIONS TO CONSIDER

Three code sections have the greatest control over wood ceiling fire codes:

• IBC 803.5 [Interiors] Interior finish requirements based on Building Group (Flame Spreads permitted)
• IBC 803.4.2 [Interiors] Set-out construction (suspended dropped ceilings)
• NFPA 13 [Sprinklers] 8.14.1  Concealed Spaces

Significantly, concern for the concealed space above the ceiling drives fire retardant code requirements. In Concealed Spaces (NFPA's term) or Dropped Ceilings (IBC's term), code and standard both demand treatment in one of three ways:

• Sprinklers,
• Class I materials on all surfaces, or
• In-fill with Class I material.

Ceilings in spaces where people work such as corridors and meeting rooms are rated Class III—mitigated sometimes by the non-use of sprinklers, the egress zone and the Occupancy Group.

• Point to Remember: The space above the wood ceiling requires fire retardant treatment. Any suspended ceiling material that interfaces with the Concealed Space must address the code. If the Concealed Space is sprinklered, you don't need a Class I wood ceiling. If there are not sprinklers, you do.

2.0 FIRE

Approximately 75% of all codes deal with Fire and Life Safety. These are critical design issues affecting virtually every aspect of building construction. The code's first priority is prevention, then rapid detection and suppression, and finally evacuation.

Fire Codes involve both fire protection and smoke protection which are addressed in the codes in several overlapping ways.

• Building Types
• Building Materials [suspended wood ceilings fall here]
• Building Systems

2.1 FIRE RATED VS FIRE RETARDANT

A clear distinction should be made between fire barrier assemblies which utilize Fire Resistant materials (Rated) and Fire Retardant materials (Indexed). The terms sound alike--and are often confused--but are quite distinct. Rated materials prevent ignition over a fixed length of time. Fire Retardant materials, on the other hand, will ignite. They slow down, however, the flame spread and smoke development of the burning material. A low flame spread material will not necessarily improve the performance of a fire rated assembly. Fire Retardant materials are commonly used by the codes for interior finish materials. Suspended wood ceilings typically fall under the jurisdiction of Section 8 Interiors.

• Point to Remember: Flame spread and smoke development values relate to the surface burning characteristics of a product. Hourly fire resistant ratings relate to the ability of a building assembly to contain a fire--such as a 1 hour wall assembly. There is a significant difference between them.

3.0 FIRE RETARDANCY

3.1 Flame Spread:

The Flame Spread Index is an arbitrary scale. The Flame Spread Index (now called the Surface Burning Characteristics Rating) fixed Concrete-board at 0 and Red Oak at 100. Note that this is a scale not a rate at which flame actually spreads along material's surface.

It works like this:

3.1.1 Steiner Tunnel Test:

The test used to calibrate a material's Flame Spread Index is called the "Method of Test of Surface Burning Characteristics of Building Materials" (NFPA No. 255, ASTM E 84, UL No. 723). It is commonly known as the Tunnel Test. A 2' x 20' sample of the material to be tested is placed along the inside top of a long metal horizontal furnace. Two ¾" open gas flames are applied at one end and a 3 mph regulated constant draft is directed through the tunnel from the flame end. The progress of the flame front along the sample is observed through side windows and timed to fix the Flame Spread Index (FSI). Smoke is also collected to fix the Smoke Developed Index (SDI).

Al Steiner, a UL engineer, developed the method in 1948 to create a repeatable, consistent test method (see www.ul.com).  9Wood uses several testing labs for our tunnel tests.

3.2 Smoke Developed Index:

A Smoke Developed Index is also measured for various materials. The Smoke Developed Index fixes 100 as the smoke development of Red Oak.

4.0 APPLYING FIRE RETARDANCY TO SUSPENDED WOOD CEILINGS

4.1 Wood's Natural Retardancy

Wood typically provides, in its natural, raw state, a Class III rating (see Fig 4).  However, some dense tropical Ironwoods, such as Ipe, provide a Class I naturally. Other species, such as true firs, receive a Class II naturally. Still, for the vast majority of species, an additive must be employed to improve the Flame Spread Index.

• Point to Remember: For most purposes, the majority of wood finishes, veneers or lumber, require some type of treatment to achieve a Class I Rating.

4.2 Obtaining a CLASS I

Several chemical processes exist to slow the flame spread and smoke developed to comply with a Class I fire rating.

4.2.1 Fire Rating Cores (for Veneered Products)

Section 8 Interiors in the Codes stipulates that if the veneer is less than 1/28" thick (having surface burning characteristics no greater than paper), then the substrate confers the Fire Retardant classification. This means that if you use Class I substrates with standard veneers, the entire assembly receives a Class I. 9Wood utilizes Duraflake FR particleboard, fabricated in Albany, Oregon by Flakeboard. Several advantages of veneers on FR cores exist, including grain and color consistency, tolerance control, and often cost efficiencies. Disadvantages are length structure limitations and difficulty of field cutting because of exposed cores.

• Point to Remember: If the core is Class I, the assembly will be Class I.

4.2.2 Fire Retardant Coatings (for Solid Wood)

Several commercial fire retardant clear coatings exist. Most discolor the final finish, or create a "plastic" looking finish. 9Wood uses a clear intumescent penetrant specially developed for 9Wood and our wood ceiling products. It seals and provides a clear top coat finish along with staining capabilities.

• Point to Remember: Solid wood requires (almost always) a topical coating treatment to achieve a Class I rating.

4.2.3 Fire Rating Impregnations

Several commercial products exist that impregnate wood or engineered wood products to deliver a Class I. These require a UL certified, pressurized tank process, and secondary kiln drying.  Wood products emerging from this process can be discolored and warped.

• Point to Remember: Pressure impregnation is not recommended for architectural wood. 9Wood has been conducting experiments using fire rated exterior plywood with a subsequent architectural veneer lamination.

5.0 CURRENT ISSUES IN SUSPENDED WOOD CEILINGS AND FIRE RETARDANCY

5.1 Exteriors

Most exterior soffits do not require Class I Flame Spread Index. Check with local code requirements. Note: California's new exterior fire codes.

5.2 LEED, FSC, NAUF & Fire Retardant cores

Currently, no FSC cores (particleboard) are made with fire retardant compounds. Recently a new FR particleboard with No Added Urea Formaldehyde (NAUF) has been test marketed . CARB (California Air Resources Board) and LEED (Leadership in Environmental and Energy Design) are championing many changes to the fabrication of commercial cores. Dilemas still remain, such as only Class III FSC (MR-7) cores, but the products available in this category are evolving constantly. Check with 9Wood for latest FR core products.

• Point to Remember: Stay in touch with 9Wood for up-dates regarding Green/Engineered wood.

6.0 RESOURCES

9Wood: Charley Coury at
UL: www.ul.com
NFPA: www.nfpa.org
American Wood Council www.awc.org
California Air Resource Board: www.arb.ca.gov
International Code Council: www.iccsafe.org
FlakeBoard: www.flakeboard.com
Sierra-Pine: www.sierrapine.com