This standard provides a test method for determining the flame spread performance in the vertical direction of plastic films and sheets with a thickness not exceeding 3 mm. The method is specifically designed for thin, flexible specimens that tend to curl under flame exposure. It evaluates the burning behavior by measuring the flaming and glowing combustion times under the influence of a specific small-flame ignition source, with results primarily used for material quality control and preliminary screening of combustion performance. The main testing instrument required for this method is a dedicated vertical flame test chamber, the core components of which include a specimen clamping device that ensures vertical fixation of the specimen, a gas (e.g., methane) burner providing a controllable low-energy flame, a sealed test chamber for safety, and a stopwatch for precise timing. Unlike the high-temperature oxygen index method you previously inquired about, this method focuses more on assessing the material's tendency for flame spread under direct ignition by a small flame.