Nfpa 99 does not define the point where a cylinder is considered empty.
Compressed gas cylinder storage nfpa.
Section 6 16 of nfpa 55 states that indoor storage and use areas and storage buildings for compressed gases and cryogenic fluids are to be provided with mechanical exhaust ventilation or natural ventilation where natural ventilation can be shown to be acceptable for the material as stored.
All storage requirements are based on the total volume of gas in cylinders being stored.
It is recommended that you only use approved storage racks so that the cylinders are adequately secured by metal chains straps or other approved materials to prevent cylinders from being knocked over.
Compressed gas cylinders can store flammable gases like acetylene and inert gases like helium.
6 storage use and handling of liquefied and nonliquefied compressed gases in laboratory work areas in accordance with nfpa 45 standard on fire protection for laboratories using chemicals a 1 1 2 6 the storage and use of compressed gases and cryogenic fluids outside the boundaries of laboratory work areas are covered by this code.