Dispel Field

In order to properly deal with magical fields, the Dispel Field spell is needed.

Spell Description
Magic fields might be useful for some magic users, but for most of them they are very annoying, if not even downright dangerous obstacles that have to be overcome. So if passage is needed through an area that is blocked by a magic field, regardless of its nature, then Dispel Field comes really in handy. Casting it will dissipate the field for the conjurer without any side-effects, freeing the way. This spell is very useful in dungeons and caves, which are notorious for their magic fields. This spell works on Energy Fields, Fire Fields, Poison Fields and Sleep Fields.

Triva

 * The Sceptre of Lord British in Ultima V can do the same, without using mana.
 * In Ultima VII Part Two, this spell is treated as a plot-related item, as only with it in the spellbook the plot can be advanced further. It is not even present in the game's documentation.