Hot-wire ignition (HWI)
Hot-wire ignition performance is expressed as the mean number of seconds needed to either ignite standard specimens or to burn through the specimens without ignition. The specimens are wrapped with resistance wire that dissipates a specified level of electrical energy.
| HWI range | PLC |
| 120 and longer | 0 |
| 60 through 119 | 1 |
| 30 through 59 | 2 |
| 15 through 29 | 3 |
| 7 through 14 | 4 |
| Less than 7 | 5 |
