The limiting electrical conditions under which ignition of coal dust and firedamp may occur have been worked at in the author's laboratory for the past 14 years, as part of a general investigation of the mechanism of ignition of gases. The paper contains an account of some results of practical interest, and deals with the electrical ignition of coal dust alone, coal dust with gas present, of methane and associated gases by disruptive sparks, steady or impulsive, transient arcs, direct or alternating, with varied voltage and frequency, in all percentages of mixture with air. Examples are given of the application of the results to promote safety in mines, notably the influence of currents of higher frequency than usual, of safety bells, safety lamps which give an alarm signal when dangerous mixtures of gas occur, and an improved earthing plate.