NASHVILLE (AP) — A Tennessee inmate is scheduled to become the second person to die in the state's electric chair in as many months Thursday evening, nearly two decades after Tennessee adopted lethal injection as its preferred method of execution.

Both David Earl Miller, 61, and Edmund Zagorski before him chose the electric chair over lethal injection, a process that proponents said would be painless and humane.

But the inmates argued in court that Tennessee's current midazolam-based method causes a prolonged and torturous death. They pointed to the August execution of Billy Ray Irick, which took around 20 minutes during which he was observed coughing and huffing before turning a dark purple.

Their case was thrown out, largely because a judge said they failed to prove that a more humane alternative was available. Zagorski was executed Nov. 1.

In recent decades, states have moved away from the electric chair, and no state now uses electrocution as its main execution method, said Robert Dunham. Dunham is the executive director of the Death Penalty Information Center, which doesn't take a stand on the death penalty but is critical of its application.

Georgia and Nebraska courts both have ruled the electric chair unconstitutional, and about two decades ago it looked as though the U.S. Supreme Court would weigh in on the issue. It agreed to hear a case out of Florida after a series of botched executions there. But Florida adopted lethal injection, and the case was dropped.

Dunham said he wasn't aware of any state other than Tennessee where inmates were choosing electrocution over lethal injection.

In Tennessee, inmates whose crimes were committed before 1999 can chose electrocution over lethal injection. Zagorski's execution was delayed about three weeks after he requested the electric chair amid a last-minute flurry of legal maneuvers. The state initially refused his request until a federal court judge ordered the state to comply.

Gov. Bill Haslam ordered a brief reprieve to "give all involved the time necessary to carry out the sentence in an orderly and careful manner."

The builder of Tennessee's electric chair warned that it could malfunction, but Zagorski's execution seemed to be carried out without incident. It was only the second time Tennessee had put an inmate to death in the electric chair since 1960.

The courts have said Miller can't challenge the constitutionality of the electric chair because he chose it, even though his attorneys have argued the choice was coerced by the threat of something even worse.

Miller was convicted of killing 23-year-old Lee Standifer in 1981 in Knoxville. Standifer was a mentally handicapped woman who had been on a date with Miller the night she was repeatedly beaten, stabbed and then dragged into some woods.

Miller has spent 36 years on Tennessee's death row, the longest of any inmate.