&37*HQHUDO5HSRUW 54. The CPT understands the term “solitary confinement” as meaning whenever a prisoner is ordered to be held separately from other prisoners, for example, as a result of a court decision, as a disciplinary sanction imposed within the prison system, as a preventative administrative measure or for the protection of the prisoner concerned. A prisoner subject to such a measure will usually be held on his/her own; however, in some States he/she may be accommodated together with one or two other prisoners, and this section applies equally to such situations. As regards more specifically the solitary confinement of juveniles, a practice concerning which the CPT has particularly strong reservations, reference should also be made to the comments made by the Committee in its 18th General Report.10 This section does not apply to the isolation of prisoners for medical reasons, as the grounds for such a measure are of a fundamentally different nature. 7KHSULQFLSOHVLQYROYHG 55. Solitary confinement further restricts the already highly limited rights of people deprived of their liberty. The extra restrictions involved are not inherent in the fact of imprisonment and thus have to be separately justified. In order to test whether any particular imposition of the measure is justified, it is appropriate to apply the traditional tests enshrined in the provisions of the European Convention on Human Rights and developed by the case-law of the European Court of Human Rights. The simple mnemonic PLANN summarises these tests. (a) Proportionate: any further restriction of a prisoner’s rights must be linked to the actual or potential harm the prisoner has caused or will cause by his or her actions (or the potential harm to which he/she is exposed) in the prison setting. Given that solitary confinement is a serious restriction of a prisoner’s rights which involves inherent risks to the prisoner, the level of actual or potential harm must be at least equally serious and uniquely capable of being addressed by this means. This is reflected, for example, in most countries having solitary confinement as a sanction only for the most serious disciplinary offences, but the principle must be respected in all uses of the measure. The longer the measure is continued, the stronger must be the reason for it and the more must be done to ensure that it achieves its purpose. 10. See CPT/Inf (2008) 25, paragraph 26.