Tests for Class 4 (Flammable Solids)
Class 4.1: Is the substance or article a Flammable Solid or Self-Reactive Substance?
For the preliminary screening test, an unbroken strip or powder train about 250 mm long by 20 mm at the base and 10 mm high is placed on a low heat-conducting plate. A gas flame (burner torch) is used to ignite the powder train at one end (minimum temperature 1000°C). If the material does not ignite within two minutes or takes longer than two minutes to burn 200 mm of the powder train, it is not considered a flammable solid. If the material ignites and propagates by either flame or smoldering through a 200 mm length in less than two minutes, then the material is considered to be a flammable solid and the burn rate tests are conducted.
Burning Rate Test
The material is filled into a 250 mm long mould with a triangular cross-section of inner height 10 mm and width 20 mm. The mould is inverted onto a plate and ignited with a small flame or hot wire. The burn rate is timed for 100 mm after the pile has been allowed to burn a distance of 80 mm. Approximately 30 to 40 mm beyond the burn rate timing zone, a wetting solution is applied to the pile in order to determine if the flame propagates through this area in 4 minutes or less. Based on the test results, Division and Packing Group classifications are assigned.
Tests for Self-Reactive Substances
Substances that are related to the self-reactive substances of Division 4.1 are distinguished from self reactive substances by the fact that the former have a self-accelerating decomposition temperature for a 50-kg package greater than 75 °C. The test determines if a material will explode or detonate when ignited under confinement. The sample is loaded into a pipe with 3000 pound pressure tested forged steel end caps. A 10-gram black powder bag igniter is inserted into the center of the pipe, the pipe is filled with test material and the ends capped. After the igniter is fired, if either the pipe or at least one of the end caps is fragmented into two or more distinct pieces then the test result is positive. The test is considered negative (the material passes) if the pipe is merely split open or the caps are sheared off in one piece. Three trials are performed unless a transition from deflagration to explosion occurs earlier.
Class 4.2: Is the substance or article a Spontaneously Combustible material?
Self-heating Substances Test
This test is performed to determine if the material in a 25 mm or 100 mm sample cube at temperatures of 100 °C, 120 °C, and 140 °C will undergo spontaneous ignition or dangerous self-heating
Class 4.3: Is the substance or article a Dangerous When Wet material?
Hazardous When Wet Test
This is a series of four tests beginning with a very small sample and gradually increasing in size up to 25 grams. The sample material is exposed to varying degrees of moisture and the reaction or gas evolution is observed and measured. Wetted materials that do not spontaneously ignite nor release more than 1 liter of flammable or toxic gas per hour per kilogram of material are not considered Dangerous When Wet.