An adverb clause should be separated from the rest of the sentence by commas if it acts as an introduction and when it's placed in the middle of the independent clause.
Explanation:
An adverb clause is a subordinate clause that acts as an adverb. Adverbs are words that modify (describe) verbs, adjectives, and other adverbs.
There are two instances when an adverb clause should be separated from the rest of the sentence by commas:
When it acts as an introduction, i.e. when it's placed at the beginning of the sentence, before the independent clause. - <u><em>When he showed up</em></u><em>, I was very surprised.</em>
When it's placed in the middle of the independent clause. - <em>My sister, </em><u><em>although she studied very hard,</em></u><em> failed the math test.</em>
