What is the difference between tunnel test methods?

Through the years, regulatory bodies in the United States, the Middle East and Canada have incorporated the Steiner Tunnel test as their standard method to evaluate fire performance of interior finish materials.

In the U.S., the Steiner Tunnel test is typically designated as ASTM E84 (or UL 723), while in Canada it is widely known as CAN/ULC-S102. Both tunnels are identical dimensionally and are run under nominally the same operating conditions. Additionally, they both stipulate similar methodologies where the specimen is mounted into the tunnel, forming the ceiling of the interior surface of the apparatus. The surface to be evaluated is exposed face-down to the ignition source. The material, product or assembly shall be capable of being mounted in the test position during the test. Thus, the specimen shall either be self-supporting by its own structural properties, held in-place by added supports along the test surface, or secured to a rigid substrate. The main differences of these tests lie in:

• the method of achieving the air turbulence necessary to ensure fuel and air mixing along the tunnel
• the terminology of the two main parameters measured during the test
• the number of replicate tests required to be performed
• the method of Flame Spread calculation

The ASTM E84 tunnel has observation windows that are two-paned, such that the inner windows are flush with the tunnel interior wall surface. Turbulence is then created by the use of six refractory firebricks at set positions along the side walls of the chamber in order to establish the air turbulence for proper mixing and combustion. The Canadian standard has single-paned windows, leaving interior recesses at each window location. It does not specify the use of turbulence-creating bricks on the tunnel floor. The turbulence is achieved by simple virtue of window recesses. Therefore, ASTM E84 has six bricks and flush windows, and CAN/ULC-S102 has recessed windows and no bricks.

Flame Spread Index (FSI) and Smoke Developed Index (SDI) are the two most important parameters used to characterize the fire performance of a sample tested in the Steiner Tunnel. The FSI is determined based on two factors, namely the rate and the total distance of the flame front propagation. On the other hand, SDI is a time integrated measurement of the obscuration of a visible light beam by smoke generated during testing of the sample. Each ASTM E84 test produces FSI and SDI, while each CAN/ULC-S102 test produces Flame Spread Value (FSV) and Smoke Developed Value (SDV). Additionally, three or more tests performed on the same material for CAN/ULC-S102 produce averaged values to create Flame Spread Rating (FSR) and Smoke Developed Classification (SDC).

Therefore, triplicate testing is a requirement for the Canadian test in both the test standard, as well as the National Building Code of Canada (NBCC).

Flame Spread Index (FSI) and Flame Spread Value (FSV) are calculated differently. The ASTM index is lower than the Canadian index by approximately 8.7%. This means that, assuming equivalence in all other factors, ASTM FSI would be 8.7% lower than Canadian FSV.

When comparing the results attained for products tested to both American and Canadian tunnel test procedures, it can be expected that the ASTM E84 and CAN/ULC-S102 flame spread numbers would show reasonable agreement – except for the 8.7% calculation difference, since typical specimen mounting is similar and the operating conditions are virtually equivalent.

With all tunnel tests, the two indices, Flame Spread and Smoke Developed, may not be directly related. Nevertheless, they help determine the applicability of a material for a particular installation requirement.

Test results

Material classifications for interior finish in accordance with ASTM E84

Interior wall and ceiling finishes, as defined by the International Building Code (IBC), are the exposed interior surfaces of buildings, including 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.

Materials are classified for their fire performance according to Flame Spread Index (FSI) and Smoke Developed Index (SDI). The Steiner Tunnel test procedure dictates calibration of the apparatus using inorganic reinforced cement board to represent zero flame spread and red oak lumber, arbitrarily assigned the FSI of 100. All tested materials are subsequently compared to red oak for relative performance. Building Codes and other documents then define and regulate the values of FSI and SDI necessary for a material to be adopted for use in a particular application. Currently, ASTM E84 (UL 723) test results for interior wall and ceiling finish materials are classified into one of the three categories as defined by industry documents such as the International Building Code and the NFPA 101 Life Safety Code.

Class A or Class 1 materials are usually required in enclosed spaces and vertical exits. Class B or Class 2 materials are permitted in exit access corridors, while Class C or Class 3 products can be used in most other areas. Materials falling outside the ranges classified above would not normally be permitted for use as interior finish in buildings. The only exception to this requirement would be if a material passes an entirely different fire performance test.

Material acceptance for interior finish in accordance with CAN/ULC-S102

Test results from CAN/ULC-S102 testing are compared to various sections of the National Building Code of Canada (NBCC). Different criteria may apply, depending on the type of building, the intended application and installation location of the material and other conditions such as the proximity to active fire suppression (sprinkler) systems. Therefore, a material may be suitable for one installation application but unsuitable for a more critical application, even within the same building.

In addition, the NBCC establishes the minimum requirements. Regional authorities with jurisdiction are free to establish their own performance criteria, so long as they are equal to, or more stringent than the national code.

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