Term used by fire codes to describe the space between the rows of back-to-back racking. Flue spaces allow the water from an overhead sprinkler system to reach lower levels of the rack. Normally a longitudinal flue space of at least 6 inches is required. It is important to note that the flue space is measured as the distance between the loads, not the distance between the racks. Also see Transverse Flue Space See article < href="/en/inventory-managment" class="q">Warehouse Fire Safety,.