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Code Q&A: Classifying Hazardous (Classified) Locations

May 22, 2025

Test your knowledge of the NEC with this challenging question.

Courtesy of www.MikeHolt.com. Based on the 2023 NEC.

Question: Hazardous (classified) locations shall be classified depending on the properties of the _____ that could be present, and the likelihood that a flammable or combustible concentration or quantity is present.

a) flammable or combustible liquid-produced vapors

b) flammable gases

c) combustible dusts or fiber/flyings

d) all of these

See answer below.

Answer: d) all of these

According to Sec. 500.5(A)(1), "Locations shall be classified depending on the properties of the flammable gase, flammable liquid-produced vapor, combustible liquid-produced vapors, combustible dusts, or fiber/flyings that could be present, and the likelihood that a flammable or combustible concentration or quantity is present."

These materials are provided by Mike Holt Enterprises in Leesburg, Fla. To view Code training materials offered by this company, visit www.mikeholt.com/code.

About the Author

Mike Holt

Mike Holt is the owner of Mike Holt Enterprises (www.MikeHolt.com), one of the largest electrical publishers in the United States. He earned a master's degree in the Business Administration Program (MBA) from the University of Miami. He earned his reputation as a National Electrical Code (NEC) expert by working his way up through the electrical trade. Formally a construction editor for two different trade publications, Mike started his career as an apprentice electrician and eventually became a master electrician, an electrical inspector, a contractor, and an educator. Mike has taught more than 1,000 classes on 30 different electrical-related subjects — ranging from alarm installations to exam preparation and voltage drop calculations. He continues to produce seminars, videos, books, and online training for the trade as well as contribute monthly Code content to EC&M magazine.