When approaching Lake Nash the pilot had selected the fuel boost pumps to low in accordance with the manufacturer's operating handbook. He started to smell fuel so he turned the pumps off. After landing he shut down and unloaded the appropriate freight. On start up he did not smell any fuel but, at about 40 knots on the takeoff run, the left wing tip exploded and the aircraft caught fire. The pilot brought the aircraft to a stop off the strip and evacuated the aircraft. He was unable to recover any of his documents before the aircraft was totally destroyed by fire. Examination by an engineer indicated that the fire may have started in the left wheel well area and that fuel vapour in the wing had exploded through the wing tip.