Archive Notice - OSHA Archive

NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.

OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at

December 3, 1979


THRU:             ROGER CLARK
                  Field Coordinator

FROM:             GROVER C. WRENN
                  Director, Federal Compliance and State Programs

SUBJECT:          National Electrical Code Interpretation

As you indicated in your July 27, 1979 memorandum, the National Electrical Code provides the requirements for a Class I, Division II area, but gives no specific criteria as far as distance is concerned, as to where a Class I, Division II area stops. Article 500-4(b) of the National Electrical Code provides the necessary criteria for properly evaluating a Class I, Division II location. It is not practical or possible for this office to replace the performance requirements with specification type (dimensional) requirements in regard to the distance that should be used on the ground level of a refinery in calculating where a Class I, Division II, area stops and where the nonclassified area begins. The complex variables involved in both cases does not permit the approach you have suggested. Compliance officers will have to use professional judgment and the performance standards to assess hazardous location requirements on a case by case basis.