NEC Art 500 and API RP 500

[Dale001289]

I just want to be completely sure on this one before I start to redline our standard details for Class I locations: a trench/sump/manhole etc is only Division 1 when the above grade classification is also classified, i.e. Division 2 or 1. If above grade is unclassified then below grade is also unclassified.

 

[Strathead]

I just want to be completely sure on this one before I start to redline our standard details for Class I locations: a trench/sump/manhole etc is only Division 1 when the above grade classification is also classified, i.e. Division 2 or 1. If above grade is unclassified then below grade is also unclassified.

As a blanket statement, I disagree. Regardless of the classification above grade, the sump would have to be rated with regards to its potential to accumulate explosive gasses in sufficient quantity to create an explosion.

 

[Dale001289]

As a blanket statement, I disagree. Regardless of the classification above grade, the sump would have to be rated with regards to its potential to accumulate explosive gasses in sufficient quantity to create an explosion.

How would explosive gases accumulate if there is no above grade source? Unless design includes 'future' process equipment, I would say your approach is overkill and would ultimately drive up cost.

 

[Strathead]

How would explosive gases accumulate if there is no above grade source? Unless design includes 'future' process equipment, I would say your approach is overkill and would ultimately drive up cost.

You asked a question,I answered it. You did not specify that there were no below or at grade sources. You asked a generic question and a generic question was answered.