With respect to Hazardous (Classified) locations, including Class I Group Classifications, certain chemical atmospheres may have characteristics that require safeguards beyond those required for any of the Class 1 groups. One such chemical may explode when mixed with air. What is that chemical?

  1. Acetylene
  2. Hydrogen
  3. Carbon disulfide
  4. Carbon monoxide.

Answer: C

According to Fine Print Note No. 3 of Section 500.6(A) of the 2008 NEC, "Certain chemical atmospheres may have characteristics that require safeguards beyond those required for any of the Class I groups. Carbon disulfide is one of these chemicals because of its low ignition temperature (90°C) and the small joint clearance permitted to arrest its flame."

Owen is the owner and president of National Code Seminars and the holder of master electrician certifications in 46 states. He can be reached at necexpert@aol.com.