Hazards Classified by NEC Group
This list is not exhaustive. It is meant only as an introductory aid to classification. Certain metal dusts have characteristics which require additional safeguards — such as extremely low ignition temperatures and energies and are therefore not included in Classes I, II or III. Class I encompasses Groups A, B, C and D; Class II contains Groups E, F, and G. Class III (fibers and "flyings") has no groups, only divisions.
- Atmospheres containing combustible metal dusts regardless of resistivity, or other combustible dusts of similar hazardous characteristics having resistivity of<105 ohm-cm (only division/zone 1, never 2; includes dusts of aluminum and magnesium and their commercial alloys)
- Atmospheres containing carbon black, charcoal, coke or coke dusts which have more than 8% total entrapped volatile material* or atmospheres containing these dustssensitized by other materials so that they present an explosion hazard, and having resistivity >100 ohm-cm but equal to or < 108 ohm-centimeter.
*Carbon black per ASTM D 1620 and charcoal coke and coke dust per ASTM D271.
- Atmospheres containing combustible dusts with resistivity of 105 ohm-centimeter or greater and not included in Groups E or F such as flour, grain,wood, plastic, and chem