This standard refers only to combustible mixtures created by dusts — such as agricultural, carbonaceous, plastic, chemical, and metal dusts. Such materials are classified in NEC ^® Article 500 as Class II, Groups E, F, and G.

This standard classifies a location based on its dust cloud concentration, its accumulated combustible dust layer thickness, and its dust bulk resistivity; it also contains references to, and data on, the explosivity of common dusts, as well as references to laboratory equipment and test procedures for evaluating the explosivity of dusts.

This standard is intended for use by persons trained in the design and installation of instrument systems and by inspection authorities in the approval of such installations.

NOTE: This standard is not intended to address hazards created by the emission of Class I combustible gases from combustible dusts, e.g., the emission of methane from freshly crushed coal.

Purpose

This standard recommends procedures for classifying locations made hazardous by the presence of a cloud or blanket of combustible dust. It conforms with the U.S. National Electrical Code ^® (NEC ^®)* and the Canadian Electrical Code (CEC), and is intended to expand and clarify both.

*National Electrical Codes^®and NEC^® are registered trademarks of the National Fire Protection Association, Inc., Quincy, Mass.