Group E (Group E has no Div. 2)
other metal alloys
1. Combustible dust may be in suspension in the air continuously, intermittently, or periodically; under normal operating conditions; or due to mechanical failure of electric equipment or protective devices.
Combustible dusts not normally present in suspension in the air in explosive quantities but where accumulation bay be sufficient to interfere with safe heat dissipation from electric equipment or may be ignited by arcs, sparks, or burning material from electrical equipment.