Solitary-confinement rules adopted by the United Nations and named for late South African leader Nelson Mandela are not binding on Canadian prisons, a federal government lawyer argued on Thursday as a two-month trial over the segregation of prisoners winds to a close.

The Mandela Rules define solitary as the confinement of inmates for 22 hours or more a day without meaningful human contact. They prohibit prolonged solitary confinement of more than 15 consecutive days.

A lawyer for the Attorney-General of Canada argued the Mandela Rules provide context, but the court is not required to adopt them. A lawyer for the plaintiffs disagreed, and said the Mandela Rules are a principle of justice.

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Mitchell Taylor, one of the lawyers for the federal government, told the court the Mandela Rules state their purpose as setting out "what is generally accepted as being good principles and practice in the treatment of prisoners and prison management."

But Mr. Taylor said to the government's knowledge no international tribunal or Canadian court has accepted the rules as binding.

"It's not that they're irrelevant, they are relevant, and they are a source of information that is before the court that you can look to to assist you in determining what you conclude are the constitutional obligations," he told the judge. "But they're not determinative."

Joseph Arvay, one of the lawyers for the plaintiffs, said he believes the rules are binding.

"I'm saying that the Mandela Rules are a principle of fundamental justice," he said.

The B.C. Civil Liberties Association and the John Howard Society of Canada are challenging the use of solitary confinement in federal prisons, arguing it violates the Charter of Rights and Freedoms, increases inmates' suffering and discriminates against offenders who are Indigenous or have mental illness. The federal government has said segregation is an appropriate and necessary tool to be used only when there is no reasonable alternative to protect the safety of a person or institution.

The court has been hearing closing arguments since Monday, and the proceedings are expected to conclude on Friday. Justice Peter Leask has indicated it could be months before his ruling is released.

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Mr. Arvay is expected to address the issue of the Mandela Rules further on Friday as he replies to the federal government's closing submission.

Earlier in the week, he described the Mandela Rules as international law.

He also argued solitary confinement causes psychological harm to nearly everyone who endures it – but Mr. Taylor said on Thursday that "serious" psychological harm must occur to cause a violation of Section 7 of the Charter, which says everyone has the right to life, liberty and security, and the right to not be deprived of them except in accordance with the principles of fundamental justice.

He said that determination was made by the Supreme Court of Canada in a 2000 ruling in which it said: "Not all state interference with an individual's psychological integrity will engage [Section 7]."

Justice Leask noted the trial heard from BobbyLee Worm, a woman who spent more than 1,100 days in solitary confinement, including one-near continuous stretch lasting more than two years.

"It sounded like her experience seemed quite serious to her," the judge told Mr. Taylor.

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The plaintiffs have also invoked the names of three people who took their lives in segregation units – Ashley Smith, Edward Snowshoe and Christopher Roy.

Mr. Taylor said there was consensus during the current Charter case that segregation causes harm and some evidence that it can cause serious harm. But he said a consensus that it causes serious harm was not reached.

The plaintiffs have said the Corrections and Conditional Release Act should be struck down, but Mr. Taylor said the Charter compliance of a law is determined by its language – not the manner in which it is administered.

He said the law should not be struck if it can be administered in a way that complies with the Charter.

Justice Leask earlier in the week questioned whether the way the solitary-confinement system is supposed to run matches reality, particularly when it comes to inmates who want to challenge their placement in a segregation cell.

The trial has focused on the current solitary-confinement regime, not a new bill introduced by the federal government in June. The BCCLA has said both the current system and the new bill fail to guarantee no individual will be held in solitary for years.

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A similar but narrower lawsuit in Ontario challenging the use of solitary confinement will resume in September.

The Globe and Mail has reported extensively on the prevalence and effects of solitary confinement, beginning with a 2014 investigation into the suicide of Mr. Snowshoe after 162 consecutive days in segregation.