This part of IEC 60079 explains the potential ignition hazard from equipment emitting optical radiation intended for use in explosive atmospheres. It covers the Groups I, II and III, EPLs Ga, Gb, Gc, Da, Db, Dc and Ma, Mb. It also covers equipment, which itself is located outside but its emitted optical radiation enters intentionally such atmospheres. It describes precautions and requirements to be taken when using optical radiation transmitting equipment in explosive gas or dust atmospheres. It also outlines a test method, which can be used in special cases to verify that a beam is not ignition capable under selected test conditions, if the optical limit values cannot be guaranteed by assessment or beam strength measurement.