i didn't explained, i usually use free weights.

let's say, bench press, 198lbs when i do this kind of lift i use bench under the fixed bar (machine, usually used for squats), if i get a power loss, just turn my wrist and the bar is locked, and that seams safe to me. This is the only cases i use machine, when i do this kind of lift.
keep in mind that i don't have a training partner, so i don't have anybody to assist me if i get with the bar on the chest, ehehe