To gain an insight into the ignition mechanisms of lightning-initiated fires, laboratory studies were made of the power and energy in lightning impulse current arcs in air along and the energy transferred to fibrous fuel materials. These studies were made with different impulse current waveforms, durations and multiplicity and with various fuel characteristics. The results indicate that lightning characteristics, such as the waveform, the duration of the impulse current and continuing current, and fuel properties such as fiber thickness, all have an influence on the power and energy transferred to the fuel and so on firing mechanisms and ignition probabilities. ¿ American Geophysical Union 1994