(54ch) Dispersion Study: An Alternative Technique for Determining Classified Area of Electrical Installations

Fire and explosion incident is an inherent risk in process facility handling hydrocarbon fluids. Any release of hydrocarbon to environment may create flammable cloud. However, fire or explosion will only occur if the cloud engulfs an ignition source.

Electrical installation is one potential source of ignition, and API RP 500 and its family are renowned recommended practices applied in the petroleum industry in regard to classifying areas in which electrical installation shall be designed to minimize ignition. They collect decades of practical experience to determine the areas where flammable cloud is normally and might occasionally present. Three-dimensional area is depicted encircling the equipment containing hydrocarbon, and is called classified area. Electrical installation shall suit its classified area or else located away outside of the area.

This paper describes an alternative technique to define the classified area for a case where API RP 500 recommendation is considered as excessive, especially for a facility having space limitation. Performing dispersion analysis to confirm the classified area will be beneficial to ensure equal level of safety assurance while optimizing the requirement for classified electrical installations.

According to API RP 500, classified area for an oily water separator pond, which is part of waste water treatment package, should extend as far as 85 feet distance horizontally. By performing dispersion analysis, the extent of classified area can be optimized down to 6 feet from the pond’s perimeter. The result is based on credible operating conditions and scenarios of the pond. By utilizing this technique, investment cost can subsequently be optimized as the number of classified electrical installation is reduced without compromising safety.