Classified area - Article 555.21

[kerickson]

In 555.21(B)(2) for classification of a motor fuel dispensing station with open construction, it states that the classified area (Class 1, Div 2) is 18" above the surface extending 20' in all directions from the dispenser. Within that 20', our site has a building with a double-walled diesel tank inside it for a fire pump that runs on diesel fuel. What is the classification of the interior of this building? Is it Class 1 Div 2 because of the 20' rule in 555.21(B)(2)(a), or is it unclassified because of the walls of the building?

 

[jatrottpe]

Not enough information to give actual answer. However, here are some things to look for to make the determination.

If there are no penetrations into the building (conduits, pipes, masonary cracks, windows, doorways)within the 20' radius and the wall is vapor tight (typically by means of a coating along exterior wall) Then the wall would act as a barrier and not let the hazardous area into the building. If there is a doorway into the building it would require a foyer, possible with an air curtain to keep the atmosphere out of the building. If the wall is cracked, compromised or not vapor tight, then the wall could let the atmosphere into the room. API RP500 and NFPA-497 have real good diagrams for additional guidance.