Flammability testing of polymeric materials - classes V-0, V-1, V-2, HB.
The standard sets out laboratory methods for testing the flammability of polymeric materials used for parts in devices and appliances. Standardized specimens are exposed to a small open flame or radiant heat source under controlled conditions and classified according to afterflame time, burning rate, afterglow, dripping of flaming particles and ignition of cotton below the specimen.
The scope excludes parts thicker than 13.0 mm or larger than 1 m² (except the Radiant Panel test) and building materials; for parts from which standardized specimens cannot be prepared, UL 1694 applies. The standard is harmonized with IEC 60695-11-10 and IEC 60695-11-20 and with ISO 9772 and 9773.
A UL 94 class describes the behavior of a material (enclosure plastic, body, insulation) under a small flame in laboratory conditions and allows materials to be compared. The class applies to a material at a specified specimen thickness, so the thickness should accompany the class in the datasheet.
The material class is not an assessment of finished-product flammability and does not demonstrate compliance with rolling-stock fire standard EN 45545-2, which has its own test methods and requirements.
HB test (horizontal): a 20 mm burner flame is applied to a horizontal specimen for 30 s and the burning rate between marks is measured; HB is achieved at ≤40 mm/min for 3–13 mm thickness, ≤75 mm/min for thickness below 3 mm, or when the flame extinguishes before the first mark.
V test (vertical): a 20 mm flame is applied twice for 10 s to the lower edge of a vertical specimen, the second time after the first flame extinguishes; each specimen’s afterflame time, total time for the specimen set, afterglow time, ignition of cotton by flaming drips and burning up to the clamp are assessed.
V-0: afterflame ≤10 s per specimen, total ≤50 s, afterglow ≤30 s, no cotton ignition, no burning to clamp. V-1: afterflame ≤30 s per specimen, total ≤250 s, afterglow ≤60 s, no cotton ignition, no burning to clamp.
V-2: as V-1, but ignition of cotton by flaming drips is permitted. 5V test (125 mm, 500 W flame) with five applications: after fifth application, flaming and afterglow ≤60 s, no dripping; 5VB permits burn-through of the plaque, 5VA does not.
The standard also includes VTM tests for thin films and HF/HBF tests for foams.
Check the class (V-0, V-1, V-2, HB, 5VA, 5VB) and specimen thickness to which it applies; “UL-VO” is a typo for V-0 (letter O instead of zero) and is not a standard number. UL 94 class applies to the material; rolling-stock fire requirements are specified by EN 45545-2 with its own test methods.
