Is it safe to use pressure-treated wood for a workbench in my shed?
Offgassing has never really been a concern with treated lumber. Direct skin contact and ingestion were concerns with CCA treatment, and to a lesser degree with the products that have replaced it. 

As long as you're not spending a lot of time in contact with wet wood, and as long as your pets and family members aren't gnawing on it, I wouldn't be concerned.