Fire Safety and Technology Editorial

 

Testing for Noncombustibility

Testing for noncombustibility is conceptually very straight-forward: a material is noncombustible if it does not ignite or burn. In actual fact, things are a lot more complicated and that can start to be seen by looking at the various ways in which noncombustible is defined.

The NFPA building code (NFPA 5000) defines it as follows: "Noncombustible Material. A material that, in the form in which it is used and under the conditions anticipated, will not ignite, burn, support combustion, or release flammable vapors, when subjected to fire or heat. Materials that are reported as passing ASTM E 136, Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750 Degrees C, shall be considered noncombustible materials." The same definition is used by most other NFPA documents.

ASTM E 176 (terminology on fire standards) defines as follows: "non-combustible, adj-not capable of undergoing combustion under specified conditions. (Contrast combustible.)". It also has a discussion saying: "In fire testing, non-combustibility is often assessed by means of Test Method E 136 or ISO 1182."

The International Building Code (IBC 2009), International Residential Code (IRC 2009) and International Fire Code (IFC 2009) do not define it. However, the IBC explains how to assess for noncombustibility, in section 703.4, as follows:

"703.4 Noncombustibility tests. The tests indicated in Sections 703.4.1 and 703.4.2 shall serve as criteria for acceptance of building materials as set forth in Sections … . The term "noncombustible" does not apply to the flame spread characteristics of interior finish or trim materials. A material shall not be classified as a noncombustible building construction material if it is subject to an increase in combustibility or flame spread beyond the limitations herein established through the effects of age, moisture or other atmospheric conditions.

703.4.1 Elementary materials. Materials required to be noncombustible shall be tested in accordance with ASTM E 136.

703.4.2 Composite materials. Materials having a structural base of noncombustible material as determined in accordance with Section 703.4.1 with a surfacing not more than 0.125 inch (3.18 mm) thick that has a flame spread index not greater than 50 when tested in accordance with ASTM E 84 or UL 723 shall be acceptable as noncombustible materials."

The International Wildland Urban Interface Code (IWUIC 2009) defines it as follows: "Noncombustible. As applied to building construction material means a material that, in the form in which it is used, is either one of the following: 1. Material of which no part will ignite and burn when subjected to fire. Any material conforming to ASTM E 136 shall be considered noncombustible within the meaning of this section. 2. Material having a structural base of noncombustible material as defined in Item 1 above, with a surfacing material not over 1/8 inch (3.2 mm) thick, which has a flame spread index of 50 or less. Flame spread index as used herein refers to a flame spread index obtained according to tests conducted as specified in ASTM E 84 or UL 723. "Noncombustible" does not apply to surface finish materials. Material required to be noncombustible for reduced clearances to flues, heating appliances or other sources of high temperature shall refer to material conforming to Item 1. No material shall be classified as noncombustible that is subject to increase in combustibility or flame spread index, beyond the limits herein established, through the effects of age, moisture or other atmospheric condition."

The International Mechanical Code (IMC 2009) defines it as follows: "Noncombustible Materials. Materials that, when tested in accordance with ASTM E 136, have at least three of four specimens tested meeting all of the following criteria: 1. The recorded temperature of the surface and interior thermocouples shall not at any time during the test rise more than 54ºF (30ºC) above the furnace temperature at the beginning of the test. 2. There shall not be flaming from the specimen after the first 30 seconds. 3. If the weight loss of the specimen during testing exceeds 50 percent, the recorded temperature of the surface and interior thermocouples shall not at any time during the test rise above the furnace air temperature at the beginning of the test, and there shall not be flaming of the specimen."

These definitions show that there are three concepts associated with noncombustible materials in the US: (a) whether they "pass" the ASTM E 136 test (which is called: "Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750ºC"), (b) whether surface layers get a good result when tested in the Steiner tunnel test and (c) whether they can degrade and then burn more.

ASTM E 136 has pass/fail criteria (which is what the IMC uses in its definition) but is careful not to state that it is a test for noncombustibility. It exposes materials to 750ºC and looks for ignition, temperature increase and mass loss. Some materials typically considered to be noncombustible have been known to fail the test (such as gypsum board). The option of testing surface layers in the Steiner tunnel was used as a way of ensuring that gypsum board (with its paper layer) can be classified as noncombustible.

In the marine world and in the realm of ISO standards, things are slightly different because there is more uniformity in the test to be used: ISO 1182 (which is called: "Reaction to fire tests for building products - Noncombustibility test"), but not in the pass/fail criteria: ISO 1182 does not have pass/fail criteria. The test method is very similar to ASTM E 136 and measures the same properties (ignition, temperature increase and mass loss) but the apparatus is different than the one in ASTM E 136. The most common set of criteria used was developed by IMO and is similar in concept but different from the ones ASTM E 136 uses.

In recent years it has become very difficult to find manufacturers of equipment to conduct tests to ASTM E 136 or of spare parts for existing equipment. With that in mind, the ASTM committee on fire standards (ASTM E05) has approved ASTM E 2652 (which is called: "Standard Test Method for Behavior of Materials in a Tube Furnace with a Cone-shaped Airflow Stabilizer, at 750°C"). This new standard test method uses the exact same apparatus and test procedure as ISO 1182 but has no pass/fail criteria. It has an appendix (non mandatory) which shows both the ASTM E 136 criteria and the IMO criteria.

Experience indicates that, for most materials, they end up being considered "noncombustible materials" whether they have been tested to ASTM E 136 or to ISO 1182 (which means also to the new ASTM E 2652). However, ASTM E 2652 was developed because codes and regulations in the US rarely use ISO standards for two reasons: (a) they often contain non mandatory language (may, should) and (b) international standards developed in the US (such as ASTM or NFPA) are preferred.

It is the expectation of many members of ASTM E05 that ASTM E 2652/ISO 1182 will be an optional alternate test to ASTM E 136. This could happen through explicit code reference to ASTM E 2652 or through the incorporation of an option into ASTM E 136 that allows testing using the ASTM E 2652 apparatus and procedure.

Direct reference to ASTM E 2652 appears to already be on its way to be recommended explicitly in NFPA 2012 codes (based on recommendations from recent NFPA 101 and NFPA 5000 committee meetings). However, it may take another cycle (i.e. ICC 2015 codes) before ASTM E 2652 can be explicitly mentioned in ICC codes, because the ICC code proposal closing dates preceded the issuance of ASTM E 2652.

Marcelo M. Hirschler