The invention provides a method and apparatus for electronically testing the safety of sources of energy such as electrical circuits, in explosive atmospheres such as high risk mining situations, using an electronic spark tester (EST) in place of the known mechanical spark test apparatus (STA). The EST typically uses an analogue subsystem (5) and a digital subsystem (6) connected by a digital to analogue converter (7) and an analogue to digital connector (8) to apply a simulated spark load to the energy source and measure the time varying current response to that load.