The hypothesis that lightning fires are caused by a special type of lightning discharge has been presented several times in literature over the past 20 years. Working with laboratory sparks, McEachron and Hagenguth [1942] suggested that ignition by natural lightning is usually caused by a discharge having a long‐continuing current phase. This view is widely accepted [Berger, 1947; Malan, 1963; Loeb, 1966], even though field corroboration has been almost nil. To the authors' knowledge, the two discharges and resultant fires documented by Norinder et al. [1958] are the only natural events reported to date wherein both the discharge and its ignition effects were documented.

Of 16 documented lightning discharges 11 caused forest fires in western Montana forests. All 11 discharges exhibited a long‐continuing current (LCC) phase of at least 40 msec duration. Of the 5 non‐fire discharges, 2 had LCC phases and 3 did not. Results to date strongly support the hypothesis that forest fires are caused by discharges with long‐continuing currents. However, available data suggest that discrete discharges (cloud‐to‐ground discharges without LCC portions) cannot be entirely ruled out as a source of forest fuel ignition.