To use a lifting belt when doing machine crunches or not.

I start my ab workouts with a weighted ab machine and am starting to get up in the weights now, but was wondering if this might be hazardous to my back or risk hernia etc? Does anyone in here use a lifting belt when doing any weighted ab exercises?
The rest of my ab workout is done with body weight, higher reps, so i was only thinking of the belt when doing weighted crunches.