Lawyers for four death row inmates who have run out of appeals are expected to argue to the South Carolina supreme court that the state’s old electric chair and new firing squad are cruel and unusual punishments.

Lawyers for the inmates also plan to argue on Tuesday that a 2023 law meant to allow lethal injections to restart keeps too many details secret about the new drug and protocol used to kill prisoners.

The death sentences of 33 inmates who are on South Carolina’s death row now hang in the balance as legal proceedings continue.

The state has not performed an execution in nearly 13 years after the drugs it used for lethal injection expired, and pharmaceutical companies refused to sell more to prison officials unless they could hide their identities from the public.

South Carolina says all three methods fit existing protocols.

A lawyer for governor Henry McMaster’s office, Grayson Lambert, said: “Courts have never held the death has to be instantaneous or painless.”

Four inmates are suing, and four more have run out of appeals. However, two of them face a competency hearing before they can be executed, according to Justice 360, a group that describes itself as fighting for the inmates and fairness and transparency in the death penalty and other major criminal cases.

South Carolina’s current execution law requires inmates to be sent to the electric chair unless they choose a different method.

Politicians allowed a firing squad to be added in 2021.

No legislation has been proposed in South Carolina to add nitrogen gas, which was used for the first time to kill an inmate last month in Alabama.

South Carolina used to carry out an average of three executions a year and had more than 60 inmates on death row when the last execution was carried out in 2011.

Since then, successful appeals and deaths have lowered the number to 33.

Facing rising costs, the lack of lethal injection drugs and more vigorous defences, they are choosing to accept guilty pleas and life in prison without parole.