National Electrical Code

Tank Farms and Conduit Sealing

Nov. 11, 2014

Oft overlooked conduit sealing requirements in bulk storage plants

Nearly all petrochemical facilities and refineries have tank farms that store feedstock or end products. The tank farms are almost always contained within diked areas. If the tank contains volatile components such as oil, gasoline, etc., then the area around the tank and within the diked area are considered to be a hazardous (classified) location as noted by the American Petroleum Institute, Recommended Practice 500 and National Fire Protection Association 497. The area immediately adjacent to the tanks is typically classified as Class I, Div. 2 to a distance of 10 ft from the tank. This classified area also extends from the tank to the dike from grade level up to the height of the dike. Any underground trenches or sumps within this area are considered to be classified as Class I, Div. 1 locations. However, there are National Electrical Code (NEC) requirements for conduit sealing that can affect underground conduit runs.

As noted in NEC Art. 515, tank farms are known as “Bulk Storage Plants.” NEC Sec. 515.9 contains specific requirements for conduit sealing. The second sentence in Sec. 515.9 states, “…Buried raceways and cables under defined Class I locations shall be considered to be with a Class I, Division 1 or Zone 1 location.” It isn’t unusual to have underground conduits entering the diked area. The conduits can serve lighting for the tank or power and controls for valve actuator motors, for example.

The rub comes in placing the conduit seals in the correct location. A conduit seal is required before the conduit goes underground near the tank, as the conduit is crossing from a Class I, Div. 2 area into a Class I, Div. 1 area. It isn’t the intent of NEC Sec. 501.15 to install another conduit seal underground where the conduit goes beneath the dike. Conduit seals should never be placed in an inaccessible location, such as buried underground. However, as soon as the conduit resurfaces outside the dike, another conduit seal should be installed as the first fitting in the conduit run.

The Photo (courtesy of Eaton Crouse Hinds) shows a typical hazardous area control station with a conduit seal below.

About the Author

Eddie Guidry | Senior Fellow

Eddie Guidry is a senior fellow with Fluor Enterprises, Inc., Sugar Land, Texas. He is highly skilled in electrical and control systems for industrial construction, design, and engineering (both domestic and abroad). The majority of Eddie’s 38 years of experience includes upstream and downstream portions of petrochemical plants and refineries. He is also heavily experienced in water and wastewater treatment facilities. Eddie is very active in the development of U.S. national (ANSI) and international codes and standards, and has been a principal member of the National Fire Protection Association (NFPA) National Electrical Code (NEC) committee since 1999 and NFPA’s National Advisory Committee on Electrical Safety Research since 2008. Eddie, who has also developed and conducted many electrical courses and seminars over the years, currently holds the corporate Master Electrician license for Fluor Corporation in the State of Texas and is also an ICC/IAEI certified electrical inspector.