- 20 c. assessment 31. Efforts are being made by the Greek authorities to improve conditions of detention in police establishments; the recent construction of new facilities in Chios Town and improvements in other police stations7 bear witness to this fact. However, certain police stations continue to hold detainees in unacceptable conditions despite previous CPT recommendations pointing out glaring deficiencies; it is necessary to ensure that appropriate conditions exist in all police detention facilities. As stated in previous visit reports, the current arrangements are particularly unacceptable for persons who remain in custody for weeks on end, in facilities such as those described above. Conditions in law enforcement establishments will frequently - if not invariably - be inadequate for prolonged periods of detention. Hence, it goes without saying that immigration detainees should not be held for extended periods, but instead should be transferred to establishments able to offer the full range of facilities and activities appropriate to their status. Having regard to Articles 3 and 10 of the Convention, the CPT calls upon the Greek authorities to take determined action to implement the recommendations outlined below in respect of the places visited and, if necessary, other places. 32. Cells should be of a reasonable size for the number of persons they are used to accommodate; for example, cells measuring 10 m², such as those at Athens Police Headquarters and Airport, should preferably hold no more than two persons overnight and never more than three. The objective in multi-occupancy cells should be to offer a minimum of 4m² per detainee. Cells should have adequate lighting (i.e. sufficient to read by, sleeping periods excluded) and ventilation and preferably should enjoy natural light. The CPT recommends that the situation as regards cell occupancy rates, lighting and ventilation be reviewed, in the light of the above remarks. Cells should be equipped with a means of rest (e.g. a chair or bench) and persons obliged to stay overnight in custody should be provided with a clean mattress and clean blankets as well as bed sheets during summer months. The CPT calls upon the Greek authorities to comply with its longstanding recommendations that all persons detained overnight be provided with a clean mattress and blankets (and bed sheets during summer months). This implies that arrangements should be made to clean mattresses and blankets at appropriate intervals. 7 cf. the response of the Greek authorities to the 2001 visit report CPT/Inf (2002) 32, pages 17 to 20.