A package that contains a category A substance cannot be transported on a passenger aircraft if it exceeds 50 mL or 50 gm.
If a category A substance exceeds 50 mL or 50 gm, it must be transported on a cargo only aircraft, The black-on-orange label, shown on the right, must be affixed to the package. This is the only label that is in compliance for cargo-only packages.
A package containing category A substances that will be sent by cargo aircraft is limited to no more than 4L or 4 kg. This volume/weight does not include ice, dry ice, or liquid nitrogen, if any of these are used as refrigerants.
Category A substances cannot be mailed via the United States Postal Service (USPS) or sent via United Parcel Service (UPS).