Here is what I see in the 5E Player's Handbook, but I do not know if this is what is actually done in BG III:
"Sculpt Spells
Beginning at 2nd level, you can create pockets of
relative safety within the effects of your evocation spells.
When you cast an evocation spell that affects other
creatures that you can see, you can choose a number
o f them equal to 1 + the spell’s level. The chosen
creatures automatically succeed on their saving throws
against the spell, and they take no damage if they would
normally take half damage on a successful save."
There is a "no damage" provision, but I also note there is a limit to the number of safe people based on the spell level. So for a fireball spell, you can spare 3+1 = 4 people.
Edit: I can’t read, apparently.
