This standard specifies the fundamental test method for evaluating the combustibility of building materials and products (such as insulation boards and decorative materials). Its core principle involves exposing a vertically positioned specimen to a small flame of fixed height (typically 20 mm) from a specified burner, applied directly to its surface or edge, without additional radiant heat. The evaluation of the material's reaction when exposed to a small flame is based on observing and recording whether the flame causes sustained combustion of the specimen, as well as the duration of combustion and the length of flame spread. This method is particularly designed to provide a direct basis for assessing the B1 and B2 fire resistance ratings of building products like insulation materials. The key specialized instrument for conducting this test is the building material combustibility tester, which typically includes a control box, a combustion chamber, a burner meeting standard requirements (e.g., with a Φ0.17 mm nozzle), an automatic ignition and timing device, and a fixture for securing and positioning the specimen.