An Alabama inmate would be the test subject for the “experimental” execution method of nitrogen hypoxia, his lawyers argued, as they asked judges to deny the state’s request to carry out his death sentence using the new method.

In a Friday court filing, attorneys for Kenneth Eugene Smith asked the Alabama Supreme Court to reject the state attorney general’s request to set an execution date for Smith using the proposed new execution method. Nitrogen gas is authorized as an execution method in three states but it has never been used to put an inmate to death.

Smith’s attorneys argued the state has disclosed little information about how nitrogen executions would work, releasing only a redacted copy of the proposed protocol.