An electrical room involving combustible dust would have explosive mixtures develop if the dust collection system failed. What would be the hazardous classification for this room?

• A. Class 2, Div 1
• B. Class 1, Div 1
• C. Class 2, Div 2
• D. Class 3

Answer: (A)

Combustible dust locations fall under Class II. The division indicates whether dust is in the air during normal operation. In a room where dust is produced and handled, dust can be suspended in the air as part of normal processes, and a failure of the dust collection system would release more dust, creating an explosive atmosphere. That means dust is present in the air under normal operating conditions (or could be released into the air if the system fails), which is why Class II, Division 1 is the appropriate hazardous classification. Division 2 would apply only if dust isn’t normally in the air and only appears under abnormal conditions, which isn’t the case here. Class 3 is for fibers, not suitable in this scenario.