This article, the first in a regular series of tutorial studies, describes in general terms the nature of explosive atmospheres, sources of ignition and electrical apparatus which can be safely used in explosion-hazardous areas. There are a number of different methods of designing electrical equipment to reduce the risk of ignition, each having a generic name such asflameproof, intrinsic safety, pressurisationetc. In later articles the philosophy and present state of development of these design concepts will be described in more detail with references to their respective applications