I've said before and say again, with the exception of installations within the Scopes of Articles 511 to 516, you cannot classify a location from the NEC itself. You must use one of the Referenced Standards in Section 500.4(B), especially Informational Note No.2. In the OP's case none of them speak directly to the mentioned process either. However, NFPA 497 - 2017, Chapter 5 does address the applicable principals and Section 5.6.4 specifically addresses "experience".
BTW unless the presence of flammable gases or vapors happens under "normal" operating conditions, i.e., when everything is operating as designed, Division 1 is inappropriate per the root definition in Section 500.5(B)(1)(1).
"Bob"
Robert B. Alexander, P.E.
Answers based on 2017 NEC unless otherwise noted.
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