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Publication 52 - Hazardous, Restricted, and Perishable Mail >
Appendix C > USPS Packaging Instruction 8C
A corrosive is any liquid or solid that causes visible destruction or irreversible alteration in human skin tissue at the site of contact or a liquid that has a severe corrosion rate on steel.
A Class 8 manufactured article that contains minute amounts of mercury (such as compact fluorescent lamps [CFLs]) that meets the standards below is permitted in domestic mail provided all the applicable requirements in 348.22g are met.
A noncombustible absorbent material that is capable of taking up all liquid in case of leakage or breakage must surround each primary receptacle.
The primary receptacle, absorbent material, cushioning material, and secondary packaging must be packed in rigid, strong outer packaging.