The Complete Guide To UL 94 Ratings

The difference between V-2 and V-0 is that V-2 is less stringent than V-0. To achieve a V-2 rating, test samples must extinguish within 30 seconds after the test flame is removed. To achieve a V-0 rating, test samples must extinguish within 10 seconds after the test flame is removed, while not burning to the top clamp or dripping molten material which ignites a cotton indicator.

The highest UL 94 rating is V-0. To achieve a V-0 rating, the test samples must extinguish within 10 seconds after the test flame is removed, while not burning up to the top clamp or dripping molten material which ignites a cotton indicator.

UL 94 HB rating indicates that the material was tested in a horizontal position (horizontal burn) and found to burn at a slower rate than a specified maximum.

The model building, life safety and fire codes include requirements that products and materials have specified minimum flammability ratings. Two UL 94 ratings that code officials commonly run across are HB and V (V-0, V-1, or V-2).

To achieve a HB rating, test samples placed horizontally burn slowly across the sample when the flame is applied to the end of the sample. For thicknesses of 3-13mm, the burning rate must be less than or equal to 40mm per minute. For thicknesses of less than 3mm, it must be less than 75mm per minute. If the flame is extinguished before the first mark, it is also awarded a HB rating.

To achieve a V rating (V-2, V-1, or V-0) test samples placed vertically with the test flame impinging on the bottom of the sample must extinguish within specified times, not burn to the top clamp and not drip molten material which ignites a cotton indicator.