For purposes of the review of exhaustion of remedies, prison administrative remedies are considered unavailable where administrators dissuade the inmate using serious threats of retaliation and bodily harm.
To establish unavailaibility, the inmate must show that the remedy was objectively out of reach to the average inmate and that he or she was actually deterred from using it.
Where a prison modifies procedure and the highest authority formally denies on the merits, the administrative remedy has been exhausted.
Housing and cellmate assignments are left to the discretionary judgment of the administrators, which bars a tort claim against the government under the FTCA exception to sovereign immunity.
http://www2.ca3.uscourts.gov/opinarch/161080p.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.