For the second time in just over a month, the doors to 20 cells at the Varner Supermax prison opened accidentally and without warning yesterday. The cells house some of Arkansas` most violent criminals. Prison spokeswoman Dina Tyler said the doors to the cells on death row were unlocked for about three minutes. No one was injured or escaped. This happened before -- a few days before Christmas. That time, an inmate was found dead in a cell with a second inmate inside. Tyler said that human error is likely the reason the doors unlocked. The Varner Supermax is near Grady in Lincoln County. It houses Arkansas` 38 death row inmates.