Often, an electrostatic ignition hazard arises when the electrostatic charge generated in a process is allowed to accumulate to levels sufficient to give rise to electrostatic discharges. Thus, the first step in an electrostatic hazard assessment is identifying where in the process electrostatic charge can be generated and accumulated. Next, if the generation and accumulation of charge cannot be controlled, the types of electrostatic discharges that can arise must be identified. Lastly, in order to verify that a hazard exists, the effective energy of these discharges must be determined and compared to the minimum ignition energy (MIE) of the prevailing flammable atmosphere or the dielectric strength of lining (the natural limitation of charge accumulation) in vessels, containers and piping.
A systematic approach for identifying electrostatic hazards is outlined in the National Fire Protection Association (NFPA) Recommended Practice # 77. This document states that an assessment of each process should be conducted to identify electrostatic hazards, including ungrounded conductors, such as metal devices and equipment, personnel, as well as items made from electrically insulating materials. The assessment should:
Be conducted under actual operating conditions, to the extent practicable;
Be based on actual measurements of resistance-to-ground, electrical continuity, electric field strength, streaming current, and accumulated charge; and
Consider prevailing environmental conditions that may affect charge generation and accumulation.
This paper discusses some of the measures that could be considered for controlling potential electrostatic hazards during liquid and powder handling operations
