Classification of explosion hazard areas for flammable gases with air density similar to that of air

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Dear experts, may I ask about the classification of explosion hazard zones for pumps used to transport dicyclopentadiene (Category A, with a relative air density of 0.98)? My consideration is: is it appropriate from a safety perspective to use a 4.5-meter length for something that is lighter than air? Also, for secondary release sources that are lighter than air and have good ventilation, with their release points at 7.5 meters above the ground level, should an explosion-proof zone be designated at the ground level of 0 meters? The regulations require that this be handled based on empirical values (but where do these empirical values come from?). For example, the platform at 11 meters high is used for carbon monoxide treatment equipment pipelines; should the pumps located at the ground level of 0 meters below it be considered as part of an explosion-proof area?