California’s prison system agreed on Tuesday to change how and when it uses solitary confinement, a decision that could reduce the number of inmates in isolation there by more than half.

The agreement settles a lawsuit brought by inmates held in isolation for a decade or more at the state’s Pelican Bay State Prison.

Solitary confinement means prisoners spend 22 hours a day or more locked in a cell with very little human contact. Plaintiffs in the case, Ashker v. Governor of California, charged that such conditions violated the Eighth Amendment’s protection against cruel and unusual punishment, and that the lack of any meaningful review of their confinement violated their rights to due process.

Under the agreement, California, which is home to the nation’s second largest prison population, agreed that it would no longer place inmates in solitary indefinitely, nor would it place inmates in solitary just because of their connection to gangs. Inmates who are currently in solitary would also have their cases reviewed as part of the agreement.

Nearly 3,000 inmates are currently in solitary units across the state. As many as 1,800 are expected to leave solitary as a result of the settlement, according to the state’s corrections department.

Inmates who are thought to be too dangerous for return to a prison’s general population unit would be placed in new wings with some social interaction and access to phone calls. Only those found to have committed major violations — like possessing a weapon, trying to escape or assaulting another prisoner — would be held in solitary.

“This settlement represents a monumental victory for prisoners and an important step toward our goal of ending solitary confinement in California, and across the country,” said the inmates who brought the suit in a written statement released by their attorneys.

A spokeswoman for California’s prison guard union, however, said Tuesday’s settlement would return the state to “the prison environment of the ’70s and ’80s, when inmate-on-inmate homicides were at the highest levels and staff were killed.”

The settlement comes amid renewed calls for prison reform, including from President Barack Obama, who became the first sitting president to visit a federal prison this summer. In July, he ordered the Justice Department to review the use of solitary confinement.

States have also begun to reexamine their use of the practice. Nebraska and Massachusetts, for example, have eliminated solitary confinement for prisoners with mental illnesses, while in January, New York’s Rikers Island jail ended solitary for inmates under the age of 21.

One factor driving calls for reform is that prisoners who spend an extended period of time in solitary can develop a rash of mental health issues, including anxiety, depression, hopelessness, anger and loss of concentration, according to Dr. Craig Haney, a psychiatrist who studies the effects of prolonged isolation on inmates. Some prisoners start losing touch with reality altogether.

“Solitary confinement is one of the tried-and-true devices that torturers worldwide engage in,” Haney told FRONTLINE in the 2013 documentary Solitary Nation, because “placing human beings in severely isolated conditions puts them in pain.”

In other words, some prisoners may leave solitary more violent than when they went in. As Rodney Bouffard, the warden of Maine State Prison, told FRONTLINE, “You can have them do their whole time in segregation, but I don’t want him living next to me when you release him.” The practice “has its place when you have real dangerous prisoners,” Bouffard said, “But from my perspective, it is overused probably throughout the United States.”

Related film: Solitary Nation

With unprecedented access, FRONTLINE covers the raw reality of solitary confinement.

Priyanka Boghani, Digital Editor, FRONTLINE

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priyanka_boghani@wgbh.org

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@priyankaboghani