Since June 2003 new and modified plants in Europe must comply with the requirements of the European Directive ATEX 137, aimed at improving the safety and health protection of workers potentially at risk from explosive atmospheres. Of all possible sources of ignition that must be considered under this legislation, the ATEX Directive draws explicit attention to one: Static Electricity.
Static is a common cause of fires and explosions, as it is present in a very wide range of industries, in some cases an inevitable outcome of the process being carried out. In others, unless specific measures have been taken, it may occur as a result of secondary actions such as movement of equipment and personnel. This paper shall firstly summarize the main characteristics of static electricity (charge generation, charge accumulation, types and modes of static discharges, such as sparks and propagating brush discharges). The paper shall then illustrate the methodology of an electrostatic risk assessment in a combustible dust environment, and the criteria to be adopted when assessing the effectiveness of the ignition. Lastly, the paper shall discuss prevention measures to reduce the electrostatic risk, such as solutions for avoiding charge generation and indications about proper grounding and bonding of conductive materials.