Class II Div 1/2 Boundary

[Richard S]

We are in the process of designing a project where the client has a large 7,500sqft room and has some equipment listed as Class II Div 1, Class II Div 2 and non-classified all going in the same room. I'm more familiar with Class I areas and use to having walls separate a classified area from an unclassified area and a seal within 10' of that boundary. I guess with Class II areas, it's more about dust control and preventing dust from propagating and accumulating. I've requested more information on what the hazardous material is. In the mean time, does anyone have experience with a single room having multiple classifications and if so, how is the demarcation of classified and non-classified determined?

Thanks

 

[rbalex]

If you are going to deal with Class II locations, you need to become familiar with NFPA 499. There are definitely some different philosophical concepts; there are also come common ones.

You are correct that material control is essential. Class II expects you to keep dust out of enclosures whereas Class I expects gases and vapors to enter enclosures no matter what you do.

It is not beyond imagination that a relatively small enclosed space (as opposed to say a large warehouse) could still have multiple classifications.

Unlike Class I, Class II does not demand a Division 2 envelope around Division 1. In fact, a Group E location can only have a Division 1 location. [See Section 500.5(C)(1)(3)]

A common concept is you first determine a location's classification, then determine suitable wiring and equipment.

These are just the tip of the iceberg.

 

[Richard S]

If you are going to deal with Class II locations, you need to become familiar with NFPA 499.

Thanks Bob. I forgot I had a copy of the NFPA 499. Reading through it, I now realize that I need to get a better understanding from the client about their equipment, the hazardous materials they are dealing with and their maintenance practices. While the wiring methods may not be as involved as class 1 areas, there sure seems to be more variables when determining the classified areas.