Packing Instruction PI 213 applies to UN 1044 Fire Extinguisher with compressed or liquefied gas. Fire extinguishers must be packed so that they cannot be activated in strong rigid outer packagings. The outer casing of a fire extinguisher by itself serves as a UN specified outer packaging, therefore the container or receptacle used for transport is regarded as an overpack.
There is no need to use a UN specification fibreboard box for the overpack. Any non-specification container strong enough to carry the weight is sufficient. However, fire extinguishers matching the stipulations of Special Provision SP A19 (c) through (e) are termed as “large fire extinguishers” and requirements of PI 213 (a) through (g) must be met.