Fire Safety and Technology Editorial

 

Steiner tunnel testing

ASTM E 84, Standard Test Method for Surface Burning Characteristics of Building Materials, also known as the Steiner tunnel test, is very widely used in North America for regulatory purposes. The test is also both loved and hated, almost in equal measure. One key reason why the test is hated is that it is often used inappropriately. The test is used for materials for which it should not be used and the test is used in ways that don't follow the spirit (or, in some cases, the letter) of what the standard intends. On the other hand tests have been conducted on so many materials over the last 50 or so years that extensive information exist to compare the fire performance of new materials with that of existing materials (as long as they are tested correctly). Two important decisions were made, one at NFPA and one at ASTM, which will help improve matters.

At NFPA, the membership approved revisions to NFPA 501, Standard on Manufactured Housing, which add the following statement to requirements for testing interior finish materials in accordance with ASTM E 84: "The test specimen shall be self-supporting so that it remains in place during the test." A valid key concern that is often expressed by opponents of this test method is that tests are conducted with the material falling away during the test and the flame exposes the area where the test specimen no longer can be found. Therefore in tests like that the flame spread on the tunnel ceiling (which is the value normally reported) is meaningless because the material is burning on the floor. This type of behavior is typical of many (but certainly not all) thermoplastic materials. In fact it has been shown that many thermoplastic materials can be properly compounded so that they remain in place during the test. For example, it is not uncommon to find test reports for tests conducted, for example on ABS material used in bathtubs, where the test report states "The test was terminated prior to 10 minutes when the temperature rise and smoke generation within the furnace chamber was deemed excessive, posing a threat to equipment. ... Early termination has no effect on flame spread when propagation reaches the end of the tunnel." It has been shown that compounds of many rigid thermoplastic materials, including ABS and polypropylene) can be manufactured so that they pass the test without falling to the floor, i.e. by remaining in place. If NFPA Standards Council upholds the action of the NFPA membership on this addition to NFPA 501, this will be one instance where inadequate testing will (hopefully) no longer happen.

At ASTM, committee E05 approved a change to the section of ASTM E 84 dealing with the test specimen. The revised section will state as follows: "The test specimen shall conform to the specimen length and width described [in the corresponding section, which requires full width test specimens] regardless of the installed width of a specific material unless the material is covered by" a few exceptions. The exceptions are of three kinds: (a) materials for which a specific test method has been developed (wires and cables for use in air-handling spaces, pneumatic tubing for control systems, combustible sprinkler piping and optical fiber and communications raceways; all of them are tested with the Steiner tunnel apparatus but with a specific test method, required for their use by the codes), (b) materials for which a specific practice has been issued with a test specimen preparation and mounting method (and none of the ones issued so far permit less than full width test specimens) and (c) adhesives, caulkings, sealants, tapes and trim, if testing at less than full width is required by the conditions of their listing and labeling. Once this is incorporated into the standard (over the next 2-3 months) no one will be able to demand that a fire test lab conduct ASTM E 84 tests of materials with specimens that are less than full width, unless they fall into the few above categories. This will affect all those who conduct tests on materials (or products) at less than full width with the excuse that their materials are not used at full width.

It is undoubtedly true that inadequate tests with the Steiner tunnel test will continue to be made. However, slowly, many loopholes are being filled and those are definitely steps in the right direction.

Marcelo M. Hirschler