Yes, it's a dependent clause—and, because it's going first, there should be a comma after it.
From "Commas with Subordinate Clauses—A Reader’s Question" at "The Editor's Blog", Beth Hill says the following:
An adverbial clause often starts with a subordinating conjunction. A short list of subordinating conjunctions:
although
after
as
because
before
once
since
though
until
when
while
A subordinate clause that stands alone is a sentence fragment . . .
When an adverbial dependent clause comes before the independent clause, we put a comma after the dependent clause (between the clauses). We don’t have to give any consideration to the topic of essential or nonessential—when the dependent clause comes before the independent, use a comma to separate them.
Note that it's a dependent clause because it wouldn't make sense on its own unless it were in response to what somebody else said:
"As a member of the rescue team."
"Sorry, what?"
but
"In what capacity did I have a terrifying experience?"
"As a member of the rescue team."
In short, in order for it to be meaningful in any way, it has to have context—either within a dialogue or linked to an independent clause in the same sentence.
