Assuming the installation is compliant with NFPA 54, electrical area classificaton largely depends on the incoming system pressure and the nature of ventilation, regulators, pressure class of valves and flanges, pressure relief systems/devices, etc.
The is no general electrical area classification requirement for closed piping systems with no valves or flanges. This should not automatically lead to the idea that systems with valves or flanges are classified, rather they should be reviewed more carefully. Regulators and relief systems will possibly lead to some level of classification depending on ventilation; e.g., NFPA 54-2018, Section 7.11.5.2. Meters alone will not usually require classification. It should be noted NFPA 54, Section 7.12 requires many NEC Article 501 wiring requirements, especially grounding/bonding - even if the location is not classified.
If the room's layout is essentially the same as those you are already familiar with, then it is reasonable to base electrical area classification on experience; e.g., see NFPA 497-2017, Section 5.6.4.
