There is no standard on the compartments, each unit can setup things thier own way.
This is the reason you see those big stickers that say "FAST PAK". Letting everyone know it's location.
Engines have two spots that don't change depending on the year of the rig. ECC compartment with all the fittings is the first lower compartment. CFRD compartment is top left rollup on newer rigs. Some older rigs will have it on the top right rollup or the one below it. Spare SCBA bottles are on the back step exept for hi-press rigs.
Trucks have preset compartments that have the Airbags and someother things but not much stays the same.