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).]

Are you working on a bulk storage plant? Article 515 only applies to bulk storage facilities for flamable liquids. Please give us more details on the installation.
Don(resqcapt19)

Don,

It looks like Big Dog may have added some information to the original post.

Bill

Big Dog,
The code does not address the area of classification except in specific locations. It only tells us how to install the wiring after the classification has been determined. This question should be addressed by the design engineer that did the original lab classification. If there is not an engineer involved, I guess I would have to be very conservative and classify an area larger than that specified in the code section that you cited. I say larger because your vent is powered and the ones in 515 are not. The force of the fan may extend the ignitable concentration a greater distance form the vent opening. Then on the other hand, it may also serve to dilute the air stream so that the vapor concentration is below the lower flammable limit making it a non classified area. There are too many variables to answer this question on a forum.
don(resqcapt19)

Don,

Once many years ago, It was suggested to me by a salesman for products for the NEC 500 series Articles, " If no one ( project engineer or owner) wants to "Classify" a hazardous area and wants the AHJ to make the classifcation, just Classify the area as the most strict possible ".

CYA.

Glenn

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