The 18-port Nose-Only Exposure Inhalation System is a derivative of the original 12-port system. It features densely packed exposure ports around the tier, allowing users to expose a significantly larger number of animals within the same workspace compared to the 12-port systems. The 18-port NOIES comes in two versions: the tall one (T) with the same tier dimensions as the 12-port system and the short version (S), specially designed for very cramped containment spaces, with only half the height of a 12-port tier. The 18-port system tiers are totally exchangeable with the 12-port tiers, i.e. users can stack up tiers from both systems in the same exposure tower.