Hi - I'm an electrician and may be able to help you with your question.
FPE or Federal Pacific Electric brand products are obsolete, and the company has been out of business for decades. There's little to find about these breakers now as a result. Different companies have either bought the company or made replacements over the years, including Reliance Electric, Challenger Electric, Connecticut Electric, American Electric to name a few.
To the dismay of electricians everywhere, the U.S. Consumer Product Safety Commission (USCPSC) investigated allegations of unsafe FPE brand circuit breakers - but could not establish that the circuit breakers pose a serious risk of injury to consumers. Check these links for the USCPSC report and opposing views:http://www.cpsc.gov/cpscpub/prerel/prhtml83/83008.html
The damage was done however. Electricians avoided installing this brand do to problems noticed. Eventually electricians began to jokingly call the FPE "Stab Lok" breakers as FPE "No Trip" breakers. They were horrible and would take a much longer time to trip in an overloaded or short circuit condition than any other circuit breaker sold. Most electricians - myself included - would try to convince property owners everywhere - to replace these panels wherever we found them. They were just that bad; in spite of the USCPSC findings.
There are many different models of FPE breakers. You should find the particular model on a label that is affixed to the breaker. Use this number when asking for information specifically about it in a follow up to my answer or whenever seeking information from other sources.
I hope this helps!