We have an application where we need to run a small instrumentation package through an oil and gas pipeline to inspect the inside for corrosion, etc. The instrument package is housed in an explosionproof case about the size of a shoebox and runs on D cell batteries. It runs completely submerged in the oil except when it is being launched or extracted, during which time it is exposed to Class I conditions. the instrument is ATEX certified, but no UL listed device is available from any manufacturer. Is a US NRTL listing required for this application? Thanks!