According to the Code, Table 515.2 (1999) or 515.3 (2002) for Vent - discharging upward, Class 1 Div 1 for area inside of vent piping or opening, Class 1 Div 1 within 3 ft of open end of vent, extending in all directions, and Class 1 Div 2 for area between 3ft and 5 ft of open end of vent, extending in all directions.

I am using an indoor Class 1 Div 2 rated dust collection system which is removing air and vapors from a Class 1 Div 2 rated area The dust collection system has two vents, one that discharges upward within 18 inches of a non-rated area and another that discharges horizontally within 30 inches of the same non-rated area.

If the dust collection system is taking in only air and vapors from a Class 1 Div 2 rated area, it should only be exhausting Class 1 Div 2 air and vapors, therefore I am unsure if Table 515.3 is applicable for this case.

Could the code be interpreted that the area within 3 ft of the open end of vent, extending in all directions, would be Class 1 Div 2? Therefore could I cover the upward discharge and only utilize the horizontal discharge and relocate to within 36 inches of the non-rated area? Would this still be in violation with the Code?

It is not a bulk storage plant. The Class 1 Div 2 rated area is a lab area. In the lab area liquids, chemicals, and solids of Group D will be used and mixed in open containers.

[This message has been edited by Big Dog (edited 11-02-2001).]