National Electrical Code

NEC Class and Division Basics

March 6, 2018

Know your hazardous location fundamentals

Hazardous locations are classified based on the properties of the combustibles in the location. A location isn’t necessarily a whole building; it can be a room or even an open area within a building.

The NEC has two classification systems:

Class and Division, as laid out in Art. 500.
Zone, as laid out in Art. 505 and Art.506 (alternate method).

A location is:

Class I if flammable or combustible vapors or gases are present in sufficient quantities to produce explosive or ignitable mixtures.
Class II if combustible dust presents the threat.
Class III if ignitable fibers or combustible flyings present the threat.
Class I is the most stringent, Class III the least.

In Class I and Class II, it’s:

Division 1 if the threat is present during ordinary conditions.
Division 2 if the threat is present during abnormal conditions.

In Class III, it’s:

Division 1 where easily ignitible fibers/flyings are handled, manufactured, or use.
Division 2 where easily ignitible fibers/flyings are stored or handled other than in the process of manufacture.
Division 1 is more stringent than Division 2.

About the Author

Mark Lamendola

Mark is an expert in maintenance management, having racked up an impressive track record during his time working in the field. He also has extensive knowledge of, and practical expertise with, the National Electrical Code (NEC). Through his consulting business, he provides articles and training materials on electrical topics, specializing in making difficult subjects easy to understand and focusing on the practical aspects of electrical work.

Prior to starting his own business, Mark served as the Technical Editor on EC&M for six years, worked three years in nuclear maintenance, six years as a contract project engineer/project manager, three years as a systems engineer, and three years in plant maintenance management.

Mark earned an AAS degree from Rock Valley College, a BSEET from Columbia Pacific University, and an MBA from Lake Erie College. He’s also completed several related certifications over the years and even was formerly licensed as a Master Electrician. He is a Senior Member of the IEEE and past Chairman of the Kansas City Chapters of both the IEEE and the IEEE Computer Society. Mark also served as the program director for, a board member of, and webmaster of, the Midwest Chapter of the 7x24 Exchange. He has also held memberships with the following organizations: NETA, NFPA, International Association of Webmasters, and Institute of Certified Professional Managers.