 The outer housing of the FOEP is a pressure-tight canister 181⁄16 inches (458.8 mm) in diameter and 18½ inches (470 mm) long.The bottom closure and removable top lid are both slightly domed to prevent implosion should pressure reversals be encountered.The inner assembly structure is fastened to a support ring approximately 6 inches from the bottom of the canister and consists of upper and lower bulkheads joined by a cylinder.