41 29. In the view of the CPT, in those cases where it is deemed necessary to deprive persons of their liberty for an extended period under aliens legislation, they should be accommodated in centres specifically designed for that purpose, offering material conditions and a regime appropriate to their legal situation and staffed by suitably-qualified personnel. The Committee is pleased to note that such an approach is increasingly being followed in Parties to the Convention. Obviously, such centres should provide accommodation which is adequatelyfurnished, clean and in a good state of repair, and which offers sufficient living space for the numbers involved. Further, care should be taken in the design and layout of the premises to avoid as far as possible any impression of a carceral environment. As regards regime activities, they should include outdoor exercise, access to a day room and to radio/television and newspapers/magazines, as well as other appropriate means of recreation (e.g. board games, table tennis). The longer the period for which persons are detained, the more developed should be the activities which are offered to them. The staff of centres for immigration detainees have a particularly onerous task. Firstly, there will inevitably be communication difficulties caused by language barriers. Secondly, many detained persons will find the fact that they have been deprived of their liberty when they are not suspected of any criminal offence difficult to accept. Thirdly, there is a risk of tension between detainees of different nationalities or ethnic groups. Consequently, the CPT places a premium upon the supervisory staff in such centres being carefully selected and receiving appropriate training. As well as possessing well-developed qualities in the field of interpersonal communication, the staff concerned should be familiarised with the different cultures of the detainees and at least some of them should have relevant language skills. Further, they should be taught to recognise possible symptoms of stress reactions displayed by detained persons (whether post-traumatic or induced by socio-cultural changes) and to take appropriate action.