Hot-Wire Ignition (HWI) - UL 746
Test specimens are wrapped with resistance wire that dissipates a specified level of energy. HWI is the time it takes to either ignite or burn through a specimen.
Performance Level Categories (PLC) were introduced to avoid excessive implied precision and bias.
|HWI Mean Ignition Time (sec)||PLC|
|120 and longer||0|
|60 through 119||1|
|30 through 59||2|
|15 through 29||3|
|7 through 14||4|