Publisher Summary This chapter explains the concept of electrical energy, ignition, and flammability. The working with electricity itself is a hazard and its use in hazardous areas requires the relevant knowledge about the dangers when designing, installing and maintaining these systems. Often the victim is not someone whose job is to install or repair electrical equipment but the employee who didn't realize that the worn electrical equipment needed replacement, or that exposed live parts were in the work vicinity. Some of the basic principles, concepts, and oft-repeated technical terms associated with electricity are discussed. The chapter briefly explains how electricity is generated and utilized. It has to traverse a long path for its transmission and utilization before it is expended into mechanical energy, chemical energy, heat energy or any other form of energy. While dealing with devices in hazardous area the designers should have adequate knowledge of the sources of heat generation. The electrical energy being a common feature in any process plant, it is necessary to study how it can be converted into heat energy. The various means in which electrical energy can be converted to heat energy are resistance heating, dielectric heating, induction heating, and leakage current heating. The chapter also presents the concept of flammability.