Definition of filter flame retardant grade

The flame retardant level increases from HB, V-2, V-1 to V-0: HB: The lowest flame retardant level in the UL94 standard. It requires that for samples with a thickness of 3 to 13 mm, the burning rate is less than 40 mm per minute; for samples with a thickness of less than 3 mm, the burning rate is less than 70 mm per minute; or it goes out before the 100 mm mark. V-2: After two 10-second burning tests on the sample, the flame goes out within 60 seconds. The burning material can fall off. V-1: After two 10-second burning tests on the sample, the flame goes out within 60 seconds. No burning material can fall off. V-0: After two 10-second burning tests on the sample, the flame goes out within 30 seconds. No burning material can fall off.