My interpretation of NFPA 497 is this:
For Class I, It is my understanding that Division 1 will always handle division 2 situations. However, Division 2 may or may not handle Division 1 situations.
Per NFPA 497 5.1.1.1 - Class I, Division 1: Ignitable gases exist under "normal conditions".
Per NFPA 497 5.1.1.2 - Class I, Division 2: Ignitable gases will normally be confined within closed containers or closed systems.
So glad I don't have to deal with this much anymore. It's usually 5 guys arguing in a boardroom for hours and hours. If you have 5 engineers draw up the area classification drawings, you will see 5 completely different drawings. There is so much room for interpretation. Plus you have guys wanting to protect their engineering firm vs the guys who have to pay the super high premium to do so. Due to the high price of electrical classification in the field, the factories tend to want to "wing" it with super high ventilation and call it good.
Hence the reason you should always say, "My interpretation of the area classification is....."
You simply can't state it factually.