http://www.unhchr.ch/html/menu3/b/h_comp36.htm
That is a link to the Body of Principles for the Protection of All Persons under Any Form of Detention or Imprisonment adopted by the general assembly of the United Nations.
Principle 6 says "No person under any form of detention or imprisonment shall be subjected to torture or to cruel, inhuman or degrading treatment or punishment.* No circumstance whatever may be invoked as a justification for torture or other cruel, inhuman or degrading treatment or punishment. "
The asterisk was linked to: " The term "cruel, inhuman or degrading treatment or punishment" should be interpreted so as to extend the widest possible protection against abuses, whether physical or mental, including the holding of a detained or imprisoned person in conditions which deprive him, temporarily or permanently. of the use of any of his natural senses, such as sight or hearing, or of his awareness of place and the passing of time."