Besides load type, packaging acceptability is one of the principal standards of
mailability. A container must not be packed in a way that might cause or allow
its contents to injure Postal Service employees or to damage other mail or
mail processing equipment. Fragile items must be packed to withstand mail
processing and transportation. Heavy items must be braced and cushioned to
prevent damage to other mail.
Items described in 1-4.2 through 1-4.5 often cause problems when
improperly packaged. Requests for exceptions to the requirements in this
section must be made to a rates and classification service center (RCSC)
(see Appendix B for addresses).
Stationery items often become loose during mail processing. Problems are
caused by unrestrained, concentrated, or shifting
contents and by inadequate internal packaging,
containers, closures, and reinforcements.
Stationery items that are thicker than 1 inch or
heavier than 1 pound may not be mailed in letter-style envelopes.
These items must be unitized by tying or banding them or by partitioning
tight containers to prevent shifting.
Liquids can damage or destroy other mail and mail processing
equipment. Generally, containers of liquid with only friction-top
closures (push-down type) are not acceptable. Screw-on caps,
soldered tops, clips, or other means are necessary for secure
Glass and other breakable containers holding more than
4 fluid ounces must be cushioned with a material that can
readily absorb any leakage. These primary containers must
be placed and packed inside sealed, leak-proof containers. If a
container holds more than 32 fluid ounces, it is not acceptable for mailing
unless cushioned as described above and packed within another sealed,
leak-proof container such as a can or plastic bag. The outer mailing container
must be strong enough to protect the contents, must be marked "LIQUID," and
should display orientation markings (i.e., up arrows) that indicate the upright
position of the parcel.
Steel pails and drums with carrying handles and positive closures (such as
locking rings or recessed spouts under screw-cap tops) are acceptable for
mailing without additional packing. Requests for exceptions to these
requirements must be made to the nearest RCSC (see Appendix B for
Aerosol containers with inadequate friction-cap
closures or other nonpositive means to
prevent accidental discharge of contents can
injure Postal Service employees or damage
other mail and mail processing equipment.
These containers must be constructed to
prevent accidental discharge of their contents in
Recessed valves, screw-thread caps, tape closures, or other secure closures
can make such containers acceptable.
High-density loads (such as tools and machine parts) can
be dangerous to Postal Service employees and to other
mail and mail processing equipment. High-density loads
that weigh between 15 and 35 pounds are machinable
on Postal Service mail processing equipment if the
loads are packaged so that they do not exert more
than 60 pounds of pressure per square foot (0.4167 pound
per square inch) on the smallest side of the mailing container.