UL 94 evaluates the burning behavior of small plastic specimens under controlled conditions. A material rating depends on specimen thickness and the report; it is not a guarantee of finished-cable or real-fire performance.
Horizontal burning HB
UL’s public explanation gives a burning-rate limit of ≤40 mm/min for specimens 3–13 mm thick and ≤75 mm/min below 3 mm. Consult the applicable complete standard for testing and classification.
Vertical burning V-0, V-1 and V-2
The flame is applied twice for 10 seconds each. This table summarizes key criteria and does not replace the complete procedure and standard.
| Criterion | V-0 | V-1 | V-2 |
|---|---|---|---|
| Afterflame time after each flame application (s) | ≤10 | ≤30 | ≤30 |
| Total afterflame time, 5 specimens and 10 flame applications (s) | ≤50 | ≤250 | ≤250 |
| Afterflame plus afterglow after the second application (s) | ≤30 | ≤60 | ≤60 |
| Burning drips ignite cotton | Not permitted | Not permitted | Permitted |
| Burning reaches the clamp | Not permitted | Not permitted | Not permitted |