ANDREW WELSH-HUGGINS,Associated Press Writer

LUCASVILLE, Ohio (AP) — Ohio has begun final preparations for executing the first person in the U.S. to die by lethal injection with a single drug rather than a three-drug method.

The execution of Kenneth Biros, originally scheduled for 10 a.m. Tuesday, was expected to begin about 11 a.m. following a delay while Biros awaited word from the U.S. Supreme Court on a last and unsuccessful emergency appeal.

In a brief statement Tuesday, the court said it was denying Biros' request for a stay of execution.

Biros had argued the state's new method would be painful. The state's switch to one drug was meant to end a lawsuit that claims the three-drug system could cause severe pain, and experts have agreed that the single anesthetic will not cause pain.

Biros would become the first person in the U.S. to die by lethal injection with a single drug, a process most death penalty experts agree will take longer than the old method.

Ohio inmates generally have taken about seven minutes to die after injection.

The Department of Rehabilitation and Correction estimates it will take from 15 to 30 minutes for Biros to die, prisons spokeswoman Julie Walburn said Tuesday.

"Every person's body absorbs drugs and processes them differently, but we don't really expect a demonstrative difference," she said.

Anesthesiologist Mark Dershwitz, who consulted with Ohio, estimated death could now come after 15 minutes.

Biros' procedure would be the first lethal injection since the state's switch last month from using a three-drug combination. If that method fails, a backup plan allows executioners to inject drugs directly into muscles instead of veins.

Walburn said Tuesday that executioners will move to that backup sooner rather than later.

"They will make a reaonsable attempt to insert the IV lines, but given that we have a backup system in place now with intramusuclar injection, we certainly don't anticipate that we would attempt that process as long as we have in the past," she said.

Biros requested and drank four cups of water late Monday night and another eight Tuesday morning, an unusual activity compared to previous executions. Walburn said she didn't know why he was drinking so much water.

Ohio overhauled its procedure after the failed attempt at rapist Romell Broom's execution, which was halted by Gov. Ted Strickland in September. Executioners tried for two hours to find a usable vein for injection, hitting bone and muscle in as many as 18 needle sticks that Broom said were very painful.

One theory is that Broom was dehydrated and his veins were harder to access.

Checks of Biros' arms Monday and again Tuesday morning found accessible veins, Walburn said.

Ohio made the change as a way to end a 5-year-old lawsuit that claims the state's three-drug system was capable of causing severe pain.

Death penalty opponents have long argued that the three drugs could cause offenders severe pain if the first drug didn't adequately knock out an inmate, and Biros' lawyers have argued the same point. The state contends that replacing the old system with a single dose of anesthetic renders Biros' complaint moot.

Injection experts and defense attorneys agree the single dose of thiopental sodium will not cause pain, similar to the way veterinarians euthanize animals. However, Biros' lawyer has argued that the new lethal-injection plan is so untested it would amount to human experimentation.

The backup procedure allowing muscle injection was created in case a situation like Broom's attempted execution happens again, to avoid painful poking around for other usable veins. The state's previous protocol didn't allow for the muscle injection.

The previous system used one drug that put inmates to sleep, a second that paralyzed them and a third that stopped their heart.

Dr. Jay Chapman, who developed the lethal three-drug cocktail in the 1970s, has said there was no particular reason he didn't propose a single drug, other than a concern that it might take a little longer to work. He has said it doesn't matter whether three fatal drugs are used or one as long as the drug works efficiently.

Other states are watching Ohio's change, but none has made a similar switch. Florida, Kentucky, South Carolina, Texas and Virginia are among those saying they will keep the three-drug method.

Biros, 51, reached the holding area for death row inmates at the Southern Ohio Correctional Facility in Lucasville on Monday morning.

In the afternoon, he was given a snack of peanut butter and jelly sandwiches. At night, he ate most of a meal of cheese pizza, onion rings, fried mushrooms, Doritos chips, French onion dip, blueberry ice cream, cherry pie and Dr Pepper soda.

He requested several cups of water throughout the evening without explanation, Walburn said. He visited with his mother, a brother and two sisters Monday and had visits from a brother and sister Tuesday. He relaxed most of the evening and slept from about 2:30 a.m. to about 6 a.m., Walburn said.

It's the second trip to Lucasville for Biros, who spent more than 30 hours in the holding cell in March 2007 before the U.S. Supreme Court stopped his execution and allowed him to challenge the state's method at the time, involving three drugs.

Biros' attorney John Parker and two friends will witness on Biros' behalf. The mother, brother and sister of Biros' victim, 22-year-old Tami Engstrom, also will witness.

Biros killed Engstrom near Warren, in northeastern Ohio, in 1991 after offering to drive her home from a bar, then scattered her body parts in Ohio and Pennsylvania. He acknowledged killing her but said it was done during a drunken rage.

A federal judge earlier Monday refused to delay the execution, and Biros immediately appealed to the 6th U.S. Circuit Court of Appeals in Cincinnati. The appeals court rejected his request for a stay Monday night, so Biros then appealed to the U.S. Supreme Court.

All 36 death penalty states use lethal injection, and 35 rely on the three-drug method. Nebraska, which recently adopted injection over electrocution, has proposed the three-drug method but hasn't finalized it.