I am not an attorney, and Google Answers cannot offer legal advice
regarding a specific situation, but there is precedent for such a
case. On February 22, 2006, the U.S. Supreme Court handed down a
decision that may be of great interest to you:
"You might think, 230 years into our history as a nation, that the
courts would long ago have decided such a basic issue as this one: can
you sue the post office if you slip and fall on mail left on your
front porch? But that question wasn't finally answered until today,
when the U.S. Supreme Court said, yes, you can.
The court ruled in favor of a Pennsylvania woman, Barbara Dolan, who
tripped over packages left on her porch instead of where her mail was
normally dropped off. The fall resulted in serious injury to her
wrists and back, so she sued the U.S. Postal Service.
Federal law allows some lawsuits against the federal government, but
there are exceptions, and the Postal Service argued that Mrs. Dolan's
was blocked by one of them -- barring claims due to the 'loss,
miscarriage, or negligent transmission of letters or postal matter.'
After all, the government said, the Postal Service delivers 660
million pieces a day to 142 million addresses and shouldn't be sued
whenever a postal customer trips on some of it.
Not so, the court concluded today. That section of the law, the
justices said, blocks lawsuits dealing only with a failure to deliver
the mail on time, in good condition, and to the right address. Just as
the Postal Service can be sued when its delivery trucks cause a
traffic accident, so it can be sued in a case like this, the justices
MSNBC: HEY, POSTMAN! WATCH WHERE YOU DELIVER
"Dolan v. United States Postal Service, 546 U.S. ___ (2006), was a
case decided by the Supreme Court of the United States, involving the
extent to which the United States Postal Service has sovereign
immunity from lawsuits brought by private individuals under the
Federal Tort Claims Act. The Court ruled that an exception to the FTCA
that barred liability for the 'negligent transmission of mail' did not
apply to a claim for injuries caused when someone tripped over mail
left by a USPS employee. Instead, the exception only applied to damage
caused to the mail itself or that resulted from its loss or delay."
Wikipedia: Dolan v. United States Postal Service
These links will supply more in-depth information on the Dolan decision:
Medill School of Journalism: Dolan, Barbara v. U.S. Postal Service, et al.
Cornell Supreme Court Collection: DOLAN v. POSTAL SERVICE Syllabus
My Google search strategy:
Google Web Search: usps legal liability "trip over"
Google Web Search: "supreme court" usps "barbara dolan"
I hope this is precisely what you needed to know. If anything is
incomplete, or if a link doesn't work for you, please request
clarification; I'll be glad to offer further assistance before you
rate my answer.