Class Codes & Rates:

 Code 4635 is applicable to the recovery of oxygen and hydrogen from the air or water. Gases are usually stored in tanks. This code is assigned to the manufacture and storage of carbonic acid gas and carbon dioxide, including the manufacture of dry ice. The charging and recharging of fire extinguishers and pressure vessels containing gas is also assigned to this code. In the liquid air process for recovering oxygen, air is subjected to a series of compression, expansion and cooling operations until it liquefies. The liquid air then goes to a fractionator where the oxygen separates from the nitrogen, argon and other rare gases such as neon, krypton, xenon and helium.