Surface flame spread measurements

The Lateral Ignition and Flame spread Test (LIFT) apparatus was developed primarily for lateral flame spread measurements. The apparatus, test procedures, and methods for data analysis are described in ASTM E 1321. A sample of 155 x 800 mm is exposed to the radiant heat of a gas-tired panel. The panel measures 280 x 483 mm. The heat flux is not uniform over the specimen, but varies along the long axis as a function of distance from the hot end as shown in Figure 14.6. The flux distribution is an invariant of distance when normalized to the heat flux at the 50 mm position. When methane or natural gas is burnt, the upper limit of the radiant heat flux is 60-65 kW/m2. The lower limit is approximately 10kW/m2 since the porous ceramic tile surface of the panel is only partly covered with flame at lower heat fluxes. 

ASTM E 286 Eight-Foot Tunnel Test. This test, a smaller version of the Steiner Tuimel Test (ASTM E 84), covers the measurement of surface flame spread of materials capable of being mounted and supported within a 13.75 in. (349-mm) x 8 ft. (2.44-m) test frame. The test also includes techniques for measuring the oke density and heat... 

The ASTM E162 test procednre [10] normally used for construction applications is nsed to test larger-sized electrical boxes or housings. The reqnirements for such are outlined in UL 94 [3]. In this test, the contribution of the sample to surface flame spread is measured under conditions where the sample is exposed to a specified radiant heat flux. Another application-specific procedure is the test for hot wires or contacts [5] according to DIN EN ISO 60695-5-1 [11] in which the sample is exposed to a glowing wire at a temperature between 550 and 960 °C. 

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. 

The surface burning characteristics (flame spread index and smoke developed index) for wood and wood products as measured by American Society for Testing and Materials (44) can be reduced with fire retardant treatments, either chemical impregnation or coatings (48). Fire retardant treatments also reduce the heat release rate of a burning piece of wood (49,50). The heat release rates (51) of the burning materials are an important factor in fire growth. 

By far the most common and most practical approach to measure the rate of flame spread over a flat surface involves recording the location of the flame tip (wind-aided spread) or flame front (opposed-flow spread) as a function of time based on visual observations. However, in the case of wind-aided flame spread, it is very difficult to track propagation of the pyrolysis front (boundary between the pyrolyzing and nonpyrolyzing fuel) as it is hidden by the flame. This problem can be solved by attaching fine thermocouples to the surface at specified locations as ignition results in an abrupt rise of the surface temperature. This approach is very tedious and not suitable for routine use. An infrared video camera has been used to look through the flame and monitor the upward advancement of the pyrolysis front in a corner fire.62... 

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 20.7 Comparison of measured and modeled HRR in room/corner test with wood lining materials. (Adapted from Carlsson, J., Computational strategies in flame-spread modelling involving wooden surfaces—An evaluation study, Lund University Department of Fire Safety Engineering, Lund, Sweden, Report 1028, 2003.)... 

Measurement of flame spread under external heat flux is necessary where the thermal radiation is likely to impinge on the textile materials, for example, the flooring material of the building or transport vehicles whose upper surfaces are heated by flames or hot gases, or both. The French test method, NF P 92-503 Bruleur Electrique or M test involves radiant panel for testing flame spread of flexible textile materials. This test method (flame spread under external heat flux) is the basis of that used by the FAA (Federal Aviation Administration) for assessing flammability of textile composites used in thermal/acoustic insulation materials (FAR 25.856 (a)) used in aircraft and has also been included by the EU for fire test approval of floorings such as prEN ISO 9239 and BS ISO 4589-1. 

In Test 3, the rates of vertical and horizontal spread of flame are measured. Pretesting is performed to find which surface of the material spreads flame the faster. This is the side to be ignited. Two timers are actuated by trip threads located horizontally at 300 mm and 600 mm above the level of application of the butane flame. A third one is connected by either of the vertical trip threads located at 75 mm on both sides of the centre line. The igniting flame is applied for 10 s. The following are observed and recorded ... 

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). 

The flame spread index (h) has traditionally indicated a material s surface flammability. The Is terminology is, however, currently in the process of being changed to the Radiant Panel Index. The I, number of classification indicates a comparative measure derived from observations made as the flame front moves across the sample surface under defined test conditions. 

In this small-scale test method, 460-mm (18-in.) x 150-mm (6-in.) wide and up to 25-mm (1-in.) thick vertical sample is used. The sample is exposed to a temperature of 670 + 4 °C at the top from a 300-mm (18-in.) x 300-mm (12-in.) inclined radiant heater with top of the heater closest to and the bottom farthest away from the sample surface. The sample is ignited at the top and flame spreads in the downward direction. In the test, measurements are made for the arrival time of flame at each of the 75-mm (3-in.) marks on the sample holder and the maximum temperature rise of the stack thermocouples. The test is completed when the flame reaches the full length of the sample or after an exposure time of 15-min, whichever occurs earlier, provided the maximum temperature of the stack thermocouples is reached. Flame spread index (7s) is calculated from the measured data, defined as the product of flame spread factor, F, and the heat evolution factor, Q. 

In the test, measurements are made for the surface temperatures (at 1(X) equidistant locations on the walls and ceiling) and length of flame on the wall (under the ceiUng) visually. After the test, visual measurements are made for the flame spread by the extent of charring on the walls and ceiling. The product is considered to have failed the test if within 15 min either ... 

ANSI/ASTM E 84-79a - method of test for surface burning characteristics of building materials (Steiner tunnel). A 24-foot-long specimen is held horizontally as the roof of a 25-foot-long chamber. The ignition source is two gas burners, applied to the underside of one end. Flame spread is measured visually and instruments are used to determine fuel contribution and smoke density. The test is identical with UL 723 and ULC-S 102 1978, used in Canadian Building Regulations. 

France NF P92-501 - radiation test for rigid materials. A 400 mmx400 mm specimen is mounted at an angle of 45° and parallel to an electrically heated radiation source. Two propane gas burners are positioned close to the upper and lower faces of the specimen, to ignite flammable gases evolved from it. The test is carried out for a total of 20 minutes and flame spread is recorded. Surface spread of flame is also measured in test method NF P92-504. 

The measurements consist of flame spread over the surface and light absorption in the exhaust duct of the timnel. Test duration is 10 min. A flame-spread index (FSI) is calculated on the basis of the area under the curve of flame tip location versus time. The FSI is 0 for an inert board, and is normalized to approximately 100 for red oak flooring. The smoke developed index (SDI) is equal to 100 times the ratio of the area under the curve of light absorption versus time for the 10-min test duration to the area under the curve for red oak flooring. Thus, the SDI of red oak flooring is 100, by definition. 

This test, also known as the radiant panel test, is one of the most widely used laboratory-scale flame-spread tests. Although not recommended for use as a basis of ratings for building code, the test does provide a basis for measuring and comparing the surface flammability of materials when exposed to a prescribed level of radiant heat energy. 

The flame-spread rating is determined by exposing the specimen to a fire at one end of a 25-ft tunnel for lOmin. The flame-spread rating is stated as a comparative measurement of the progress of flame over the surface of the tested material on the 0-100 scale where inorganic reinforced cement board is rated at 0 and red oak is rated at 100. A photoelectric cell is used to measure the smoke density. 

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