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Trends in Interior Finish Requirements
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Issue 16: Trends in Interior Finish Requirements

By Marcelo M. Hirschler, Ph.D.

Codes, especially building and fire codes, regulate the fire properties that must be exhibited by interior finish materials that are used in regulated building environments.

Interior finish, as regulated by codes in the U.S., can be subdivided into four types of materials or products: interior wall finish, interior ceiling finish, interior floor finish and trim. The International Building Code®1 defines as follows:

  • Interior floor finish: the exposed floor surfaces of buildings including coverings applied over a finished floor or stair, including risers.
  • Interior wall and ceiling finish: the exposed interior surfaces of buildings, including but not limited to: fixed or movable walls and partitions; toilet room privacy partitions; columns; ceilings; and interior wainscoting, paneling or other finish applied structurally or for decoration, acoustical correction, surface insulation, structural fire resistance or similar purposes, but not including trim.
  • Trim: picture molds, chair rails, baseboards, handrails, door and window frames, and similar decorative or protective materials used in fixed applications.

Not much has changed in terms of the basic interior finish requirements for fire performance in the U.S, for many years. The requirements are as follows:

  1. Interior wall and ceiling finish materials (and interior trim) are tested using the Steiner tunnel test, ASTM E 84.2 The pass/fail criteria used by the codes for this test are:
    Class A: Flame spread index: ≤ 25 – Smoke developed index: ≤ 450
    Class B: Flame spread index: > 25 & ≤ 75 – Smoke developed index: ≤ 450
    Class C: Flame spread index: > 75 & ≤ 200 – Smoke developed index: ≤ 450
  2. Interior floor finish materials are tested using the flooring radiant panel test,
    ASTM E 6483 or NFPA 2534 (which are equivalent). The pass/fail criteria used by the codes for this test are:
    Class I: Critical radiant flux: ≥ 0.45 W/cm2
    Class II: Critical radiant flux: ≥ 0.22 W/cm2 & < 0 .45 W/cm2

Once these basic concepts were set up, exceptions and clarifications have gradually been added, because some types of materials are considered to have unusual fire performance characteristics. Thus, for example, exceptions were put in place for trim because there was very little of it, and special requirements were put in place for foam plastic insulation because testing in accordance with ASTM E 84 gave misleading results. Also, very thin materials (< 0.9 mm thick) and structural wood were exempt from testing.

In the 1990s, room-corner tests were allowed as alternate tests to the Steiner tunnel test. The key room-corner test is NFPA 286,5 which is now applicable to all interior wall and ceiling finish materials. Just like ASTM E 84 and ASTM E 648 or NFPA 253, the NFPA 286 test method itself does not contain approval requirements. The pass/fail criteria U.S. codes apply for regulating materials that are tested using NFPA 286 are: no flashover, peak heat release rate of 800 kW, no flame spread to the corners of the ceiling, and a total smoke release not exceeding 1,000 m2. If a material meets the above NFPA 286 criteria, it is allowed anywhere that a Class A material (in accordance with ASTM E 84) is required. No definitive studies have shown equivalence between the pass/fail criteria for both tests, but consensus exists that materials which release little heat and smoke, and don't go to flashover in the room-corner test are likely to exhibit reasonable fire performance.


So, are trends flat? In fact, no, since a lot of improvements are underway, principally in terms of tightening loopholes. The three key examples of activity follow.

Specific requirements associated for certain materials or products

  1. Textile and expanded vinyl wall and ceiling coverings have been shown to give potentially misleading results (because the samples are very thin). Therefore, if they are tested only with ASTM E 84, they normally require sprinkler protection. Moreover, an alternate room-corner test, NFPA 265,6 was designed for textile wall coverings, but cannot be used for ceiling coverings (because the flame does not reach the room ceiling). The screening test option (Method A) in NFPA 265 is also being eliminated.
  2. Foam plastic materials must be tested using NFPA 286 (even when they have a textile or vinyl covering) or they must be covered with a thermal barrier. The thermal barrier itself needs to protect the foam plastic for 15 minutes and cannot contribute to the fire.
  3. Trim is allowed to exhibit poorer fire performance than interior finish if it covers less than 10 percent of the wall or ceiling. Foam plastic trim also has thickness and density limitations.
  4. Interior floor-wall base, up to a width of 152 mm, is tested in accordance with ASTM E 648 instead of using ASTM E 84 or NFPA 286.
  5. Many surfaces, such as movable walls and partitions, paneling, wall pads and crash pads, are being considered interior finish materials as a whole and not decorations, nor is the top layer considered just a stand-alone wall covering.

Steiner tunnel mounting practices

The standards that describe Steiner tunnel testing have tended to leave broad discretion to the labs (and to the test sponsors) in how to prepare test specimens and mount them during the test. This has resulted in some excesses, including testing of individual components instead of systems (when the fire performance of a system can be very different from the combined fire performance of the individual materials, such that each layer can meet requirements while the system does not), allowing materials to melt and continue burning on the floor while reporting ceiling flame spread (which of course would not happen of the material is on the floor), placing materials in contact with heat sinks (such as chicken wire), filling materials with water to minimize visible flame spread, testing materials at less than full width and many others. Committee ASTM E05, on Fire Standards, has now developed four standard practices, to make testing of some materials fully standardized. They are ASTM E 22317 (pipe and duct insulation materials and systems), E 24048 (textile, paper or vinyl wall or ceiling coverings), E 25739 (site-fabricated stretch systems) and E 257910 (wood products). Reference to all of these practices is being gradually added to ASTM E 84, while relying less on the appendix guidance sections. Work is underway on several other practices, including ones intended to apply to reflective insulation systems and vapor barriers.


Materials in plenums

The basic requirements for materials in plenums are that the material exhibit Steiner tunnel pass/fail criteria of a flame spread index not greater than 25 and a smoke developed index not greater than 50. However, special criteria need to be in place for some materials, including foam plastic insulation, which cannot be tested properly in the Steiner tunnel and require added criteria.

Interior finish materials are key components of the fire safety of a building, and therefore, the more is known about the materials used, the more efficiently and appropriately they can be tested, and regulated, for better fire safety of the building's users.

  1. International Building Code®, International Code Council, Washington, DC., 2006.
  2. ASTM E 84: Standard Test Method for Surface Burning Characteristics of Building Materials, ASTM International, West Conshocken, PA, 2007.
  3. ASTM E 648: Standard Test Method for Critical Radiant Flux of Floor-Covering Systems Using a Radiant Heat Energy Source, ASTM International, West Conshohocken, PA, 2006.
  4. NFPA 253: Standard Method of Test for Critical Radiant Flux of Floor Covering Systems Using a Radiant Heat Energy Source, National Fire Protection Association, Quincy, MA, 2006.
  5. NFPA 286: Standard Methods of Fire Tests for Evaluating Contribution of Wall and Ceiling Interior Finish to Room Fire Growth, National Fire Protection Association, Quincy, MA, 2006.
  6. NFPA 265: Standard Methods of Fire Tests for Evaluating Room Fire Growth Contribution of Textile Coverings on Full Height Panels and Walls, National Fire Protection Association, Quincy, MA, 2007.
  7. ASTM E 2231: Standard Practice for Specimen Preparation and Mounting of Pipe and Duct Insulation Materials to Assess Surface Burning Characteristics , ASTM International, West Conshocken, PA, 2007.
  8. ASTM E 2404: Standard Practice for Specimen Preparation and Mounting of Textile, Paper or Vinyl Wall or Ceiling Coverings to Assess Surface Burning Characteristics , ASTM International, West Conshocken, PA, 2007.
  9. ASTM E 2573: Standard Practice for Specimen Preparation and Mounting of Site-Fabricated Stretch Systems to Assess Surface Burning Characteristics , ASTM International, West Conshocken, PA, 2007
  10. ASTM E 2579: Standard Practice for Specimen Preparation and Mounting of Wood Products to Assess Surface Burning Characteristics , ASTM International, West Conshocken, PA, 2007.

Marcelo M. Hirschler is with GBH International.

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