An ignitable material (26) is positioned in contact with a slag (8) contained in a plasma arc treatment system having an electrode (10) and an electrical ground (14). The slag is initially at a temperature below a conducting temperature at which the slag will conduct electricity between the electrode and the grounding network. The ignitable material has a self-sustaining reaction which releases heat energy upon ignition. The ignitable material is ignited with a pilot arc (28) thereby heating at least a portion of the slag to the conducting temperature so that an arc between the electrode and the grounding network can be sustained.