Steiner Tunnel

ASTM E84, UL 723, UL 910 Steiner tunnel flame spread and smoke... 

The PVC formulations shown in Table 2 represent typical compounds used by the wine and cable industry. PVC compounders have developed new PVC-based formulations with very good fire and smoke properties (can pass the UL 910 Steiner Tunnel test) that compete with the more expensive fluoropolymers. These can be used in fabricating telecommunication cables usable for plenum area appHcations. 

Metal deck assemblies are tested by UL for under-deck fire hazard by using their Steiner tunnel (ASTM E84). The assembly, exposed to an under-deck gas flame, must not allow rapid propagation of the fire down the length of the tunnel. FM uses a calorimeter fire-test chamber to evaluate the hazard of an under-deck fire. The deck is exposed to a gas flame and the rate of heat release is measured and correlated to the rate of flame propagation. A different FM test assesses the damage to roof insulations exposed to radiant heat. 

As mentioned earlier, the fire hazard of interior finish materials is primarily due to the potential for rapid wind-aided flame spread over the surface. It is therefore not a surprise that reaction-to-fire requirements for interior finish materials in U.S. building codes are primarily based on performance in a wind-aided flame spread test. The apparatus of this test is often referred to as the Steiner tunnel. The Steiner tunnel test is described in ASTM E 84. Although the test does not measure any material properties that can be used in a model-based hazard assessment, a discussion of the test is included here due to its practical importance for the passive fire protection of buildings in the United States. 

FIGURE 14.11 ASTM E 84 Steiner tunnel test apparatus. Left insert Burner flame viewed from tunnel inlet. Right insert Initial flame tip location is 1.37m (4.5 ft) from the burner. (Photo courtesy of Southwest Research Institute, San Antonio, TX.)... 

Janssens M, Huczek J, Sauceda A. Development of a model of the ASTM E84 Steiner tunnel test. Ninth International IAFSS Symposium. Interscience Communications Ltd. Greenwich, London, 2008. 

Chapter 7 is the chapter dealing with Special Conditions and it addresses most of the cables with highly improved fire performance. Thus, Articles 725 (Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits), 760 (Fire Alarm Systems), and 770 (Optical Fiber Cables and Raceways) all use the same two schemes for fire performance of cables, as shown in Figures 21.4 and 21.5. The figures show that the best is NFPA 262,65 a cable fire test for flame spread and smoke, conducted in a modified Steiner tunnel (86 kW or 294,000 BTU/h), for which the requirements in the NEC are that the maximum peak optical density should not exceed 0.5, the maximum average optical density should not exceed 0.15, and the maximum allowable flame travel distance should not exceed 1.52m (5 ft). The next test, in the order of decreasing severity is UL 1666,64 known... 

The requirements for interior finish are very similar to those in the IBC and IFC, except that it is less comprehensive, does not address some materials such as HDPE or site fabricated stretch systems, and does not include the requirement to apply any of the standard practices for use of the Steiner tunnel, ASTM E 84. This is partially owing to the longer period between the proposals and issuance of a new code. 

In terms of fire safety, there are no fire resistance requirements and all interior surfaces must comply with the FSI of 200 in the Steiner tunnel test, ASTM E 84,114 or a radiant panel index of 200 in the radiant panel test, ASTM E 162.55 Thermal insulation materials, other than foam plastics, must meet an ASTM E 84 Class A requirement (i.e., FSI < 25 and SDI < 450) and loose-fill insulation must meet the same requirements as the building codes, which are mostly based on smoldering tests (as the materials tend to be cellulosic). Foam plastic insulation must be treated as in the building codes as well (see Table 21.13) it cannot be used exposed (expensive foam that meets the NFPA 286 test is not used in manufactured housing) and must meet an ASTM E 84 Class B requirement behind the thermal barrier. 

ASTM E 84 Steiner tunnel test, thus generating more useful results. Figure 21.13 shows a room-comer test layout. The cone calorimeter fire-performance index (with tests conducted at 50kW/m2)179 was shown to be a good predictor of time to flashover in FAA full aircraft fires170 180 and in the ISO 9705 room-corner test.181 In addition, the same cone calorimeter tests, but using only heat release criteria, have been shown to have almost perfect predictability of ISO 9705 room-comer test rankings.181... 

The majority of the materials with low flame spread (or low heat release) also exhibit low smoke release. However, it has been shown in several series of room-corner test projects (with the tested material lining either the walls or the walls and the ceiling), that -10% of the materials tested (8 out of 84) exhibited adequate heat-release (or fire growth) characteristics, but have very high smoke release (Table 21.17 and Figure 21.16).189190 These materials would cause severe obscuration problems if used in buildings. A combination of this work, and the concept that a visibility of 4 m is reasonable for people familiar with their environment,191 has led all the U.S. codes to include smoke pass/fail criteria when room-corner tests are used as alternatives to the ASTM E 84 Steiner tunnel test. 

Within ASTM, technical committees associated with plastics, electrical materials, textiles, protective clothing, thermal insulation, consumer products, detention and correctional facilities, and ships have developed tests that are often application tests that are of specific interest to the products involved. One fire test has spawned more application standards than any other, primarily because of its vast use in the United States ASTM E 84 (Steiner tunnel). Thus, NFPA 262, UL 1820, UL 1887, ASTM E 2231, ASTM E 2404, ASTM E 2573, ASTM E 2579, and ASTM E 2599 are all test methods and practices based on the Steiner tunnel test. In some cases, the base apparatus is being modified (although usually it is permissible to conduct the ASTM E 84 test in the apparatus of the other test, but it is often not permissible to conduct the other test in any apparatus complying with the ASTM E 84 apparatus). The other test method that has resulted in many application standards is the cone calorimeter the standards are ASTM D 5485, ASTM D 6113, ASTM E 1474, ASTM E 1740, and ASTM F 1550. 

The Steiner Tunnel test (ASTM E 84) is used to classify the fire-spread potential of products used in wall and ceiling linings [4], and is used to classify expanded polystyrene foam. In this method, specimens are placed on the ceiling of a 24 ft long tunnel. An 88 kW natural gas burner is placed at one end of the tunnel and a forced-air draft with a velocity of 1.22 m/s is introduced. The flame spread is recorded as a function of time and an arbitrary index is calculated from the measurements. 

This test has been criticized because it does not simulate actual building fire conditions [5,6], An additional problem with foamed samples is that the specimens either retract out of the reach of the flame or drip on to the floor of the tunnel. In Canada this has been addressed by using a downward-facing burner and mounting the specimens on the floor of the tunnel. Despite its limitations, the Steiner Tunnel method continues to be used to test and rate thermoplastic foams. 

Because expanded polystyrene foam is processed at a lower temperature, aliphatic bromine compounds such as hexabromocyclododerane (HBCD) can be used for this application. The flame retardant levels in these systems are family low, typically less than 3wt%. These levels are sufficient to pass the Steiner Tunnel test, and synergists such as antimony trioxide are not necessary. 

ASTM E 84 Steiner Tunnel Test. This test, which uses very large samples (20 ft x 20 1/4 in.) is referenced in all model building codes for evaluating flame spread and smoke emission of foam plastic insulation. The test apparatus consists of a chamber or tunnel 25 ft. long and 17 3/4 X 17 5/8 in. in cross section, one end of which contains two gas burners. The test specimen is exposed to the gas flame for ten minutes, while the maximum extent of the flame spread and the temperature down the tunnel are observed through windows. Smoke evolution can also be measured by use of a photoelectric cell. The flame spread and smoke evolution are reported in an arbitrary scale for which asbestos and red oak have values of 0 and 100, respectively. More highly fire-retardant materials have ratings of 0-25 by this method. 

This is called the Steiner Tunnel Test. Very large samples are required. 

In the Steiner Tunnel of ASTM E 84-1981a (cf. Section 3.2.1, Fig. 3.93), flame spreading is measured on a specimen with surface area of 7320 mm x 508 mm. In the horizontal vent pipe of 408 mm dia. at the outlet of the tunnel, changes in the intensity of a vertical light beam are recorded during the test procedure. The area under the intensity vs, time curve for the specimen is divided by that for a red oak specimen and multiplied by 100, to establish a numerical index for comparison of the performance of the material to that of an asbestos-cement board and of red oak, taking these as limit points of an arbitrary centesimal scale (0 and 100, respectively). 

In addition to smoke suppressors, reduced-smoking compounds are also available in a ready-to-process state. For example the Envirez grade of PPG Industries is a styrene-free polyester resin filled with alumina trihydrate. Its smoke production is between 10 and 100 according to ASTM E 84 measured in the Steiner Tunnel (cf. Fig. 3.93, Section 3.2.1), and its value in the NBS chamber (cf. Fig. 4.6, Section 4.1.1.4) is 89, while those of the conventional halogen-containing flame-retarded polyesters are 250 to 1100 (smoke production) and 102 (D value). 

Full-scale fire tests can give more useful information than small-scale tests with tiny specimens. They can simulate the behaviour of plastics articles such as foam-filled furniture and television sets in fires. Examples include the Steiner tunnel test, the ISO 9705 room comer test and the CAL 133 test. Many fire test procedures are specific to a given industry, such as construction or the railways. In the latter case, the standard of flammability required may depend on whether a train is to be operated through long tunnels. 

Steiner tunnel tests (ASTM E84) [127] measure the surface flame spread of a material. The specimen is exposed to an ignition source, and the rate at which the flames travel to the end of the specimen is measured. The severity of the exposure and the time a specimen is exposed to the ignition source are the main differences between the tunnel test methods [119]. The data obtained provide a measure of fire hazard, in that flame spread can transmit fire to more flammable materials in the vicinity and thus enlarge a conflagration, even though the transmitting material itself contributes little fuel to the fire. 

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