Focus Article - Beyond Hazardous Area Classification
In explosion and flash fire incidents, electrical arcs and electrostatic sparks are often considered to be primary ignition sources, because they are “everywhere” and can have sufficient energy to ignite most flammable gases and vapors and dense clouds of many combustible dusts.
However, there is a wide variety of other types of ignition sources; they include the following [References 1, 2, and 3], presented in the descending order of the likelihood and risk of ignition hazards in a chemical plant: