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?
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."
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