In the UL94 plastic flammability rating system, there are a total of 12 classifications: HB, V-0, V-1, V-2, 5VA, 5VB, VTM-0, VTM-1, VTM-2, HBF, HF-1, and HF-2.
Plastic combustion test
The flammability UL94 rating is the most widely applied standard for the flammability of plastic materials. It is used to evaluate the ability of a material to extinguish after being ignited. There are various methods of assessment based on the burning rate, burning time, drip resistance, and whether the dripping particles continue to burn. Each material tested can receive numerous values depending on its color or thickness. When selecting a material for a product, its UL rating should meet the thickness requirements of the plastic part's wall section. The UL rating should be reported along with the thickness value, as reporting the UL rating without the thickness is insufficient.
The flammability rating of plastics increases progressively from HB, V-2, V-1, V-0, 5VB to 5VA:
HB: The lowest flame-retardant level in the UL94 standard. It requires that for samples with a thickness of 3 to 13 millimeters, the burning rate must be less than 40 millimeters per minute; for samples less than 3 millimeters thick, the burning rate must be less than 70 millimeters per minute; or the flame must extinguish before reaching the 100-millimeter mark.
V-2: After subjecting the sample to two 10-second flame tests, any afterflame & afterglow extinguishes within 60 seconds. Dripping particles can ignite cotton.
V-1: After subjecting the sample to two 10-second flame tests, any afterflame & afterglow extinguishes within 60 seconds. Dripping particles cannot ignite cotton.
V-0: After subjecting the sample to two 10-second flame tests, any afterflame & afterglow extinguishes within 30 seconds. Dripping particles cannot ignite cotton.
5VB: After subjecting the sample to five 5-second flame tests, any afterflame & afterglow extinguishes within 60 seconds. Dripping particles cannot ignite cotton. For solid samples, burn-through is allowed.
5VA: After subjecting the sample to five 5-second flame tests, any afterflame & afterglow extinguishes within 30 seconds. Dripping particles cannot ignite cotton. For solid samples, burn-through is not allowed.