Carbon dioxide (CO2) and other nonflammable, nontoxic gases
Quantity limit: Up to four cartridges/cylinders containing nonflammable gas may be carried. Each cylinder must not exceed 50 ml (equivalent to 28 g carbon dioxide cartridge).
May be carried in checked baggage only.* Airline approval is required.
Cartridges/cylinders not installed in the device should be securely packed.
Compressed gas cylinders, canisters, and cartridges with a volume larger than 50 ml are forbidden in baggage unless covered by another exception in this table.
For air guns and similar devices, see TSA's security rules.
*Though allowed in carry-on baggage and checked baggage under U.S. and international hazardous materials regulations, TSA security rules allow these cartridges in checked baggage only.
Regulation that allows it: 49 CFR 175.10(a)(25)