NFPA 270-2018 Standard Test Method for Measurement of Smoke Obscuration Using a Conical Radiant Source in a Single Closed Chamber.
6.3* Number of Specimens. 6.3.1 A minimum of six specimens shall be tested, so that three specimens are tested at each of the two required condi‐ tions. 6.3.2 Unless otherwise specifed by the test requester, the standard exposure conditions shall be as follows: (1) Flaming at an irradiance of 25 kW/m 2 (2) Flaming at an irradiance of 50 kW/m 2 6.4 Additional Specimens. 6.4.1 An additional number of specimens, as specifed in Section 6.3, shall be used for each face in accordance with the requirements of Section 6.2. 6.4.2 An additional six specimens (three specimens per mode to be tested) shall be held in reserve, in case they are required by the conditions specifed in 9.9.2. 6.5 Size of Specimens. 6.5.1 Size. The specimens shall be square with sides 75 mm. 6.5.2 Thickness. Whenever possible, test samples shall be in their end- use thickness. Samples used with a thickness of 25 mm or less shall be evaluated at their full thickness. Records shall be kept of specimens’ thicknesses and, if required, their masses. 6.6.2 If fat sections of the same thickness and composition are tested in place of curved, molded, or specialty parts, this difference shall be stated in the test report. 6.6.3 Any substrate or core materials for the specimens shall be the same as those used in practice. 6.6.4 When coatings, including paints and adhesives, are tested with the substrate or core as used in practice, specimens shall be prepared following 6.6.1, and in such cases the method of application of the coating, number of coats, and type of substrate shall be included in the test report. 6.7 Wrapping of Specimens. 6.7.1 All specimens shall be covered across the back, along the edges, and over the front surface periphery leaving a central exposed specimen area of 65 mm ± 5 mm × 65 mm ± 5 mm, with a single sheet of aluminum foil that is 0.04 mm ± 0.005 mm thick with the dull side in contact with the speci‐ men. Care shall be taken not to puncture the foil or to intro‐ duce unnecessary wrinkles during the wrapping operation. The foil shall be folded so as to minimize losses of any molten material at the bottom of the holder. After the specimen is mounted into its holder, any excess foil along the front edges shall be trimmed off. 6.7.2 All wrapped specimens shall be backed with one or more sheets of noncombustible insulating board of an oven-dry density of 850 kg/m 3 ± 100 kg/m 3 and a nominal thickness of 12.5 mm to ensure that the top edges of the specimen are pressed against the retaining lips of the specimen holder. 6.7.3 Wrapped specimens less than 25 mm thick shall be backed with at least one sheet of noncombustible board with or without a layer of refractory mineral fber blanket underneath to accommodate a wider variety of specimen thicknesses as described in
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