Includes tank charging.

Code 4635 applies to employers engaged in recovery of oxygen and hydrogen from air or water.  This classification also includes manufacturing dry ice.  Carbonic acid is the weak acidic water solution of carbon dioxide and is used in soft drinks and carbonated beverages to provide the fizz and sparkle. 

This classification also includes tank charging/filling.  Gases such as oxygen, nitrogen, acetylene, argon and nitrous oxide may be purchased from outside suppliers in bulk and stored in tanks.  Empty tanks are received from customers where they are tested for leaks, blown out for remaining excess gas, refilled and delivered to the customer.  Some employers purchase oxygen and nitrogen in a liquified form and store it in bulk containers.  The liquid is then vaporized in a vaporizing machine into gas and filled into cylinders.