As it has been said many times on this forum, the AHJ is the boss. As soon as the inspector told @Southernhighlander that the manway is a fill opening, this code became part of the discussion.
NFPA 30 Table 7.3.3 Drum and container filling – outdoors or indoors – NEC Class 1, Div 1, Zone 1 within 3’ of the vent or fill opening, extending in all directions. NEC Class 1, Div 2, Zone 2 from 3’ to 5’ from the vent or fill opening, extending in all directions; also, up to 18” above floor or grade level within a horizontal radius of 10 ft from the vent or fill opening. Also, Div 1 for the trench below floor level.