Learn German: Ich arbeite hiermit, sofern das Labor frei ist. - I am working with this, provided that the lab is free.

When referring to inanimate objects or abstract ideas (like a tool or a chemical in the lab), German prefers combining hier- with a preposition rather than using the preposition with a pronoun. hiermit literally means "here-with" or "with this." If you were talking about working with a specific person, however, you would have to use mit diesem or mit ihr/ihm.

What kind of word is sofern and how does it affect the sentence structure?

sofern is a conditional subordinating conjunction that translates to "provided that" or "as long as." Because it is a subordinating conjunction (just like weil or dass), it kicks the conjugated verb (ist) to the very end of its clause.

Could I just use wenn instead of sofern here?

Yes, replacing it with wenn works perfectly fine grammatically (..., wenn das Labor frei ist). However, sofern is slightly more formal and precise. While wenn can mean either "if" or "when," sofern strictly sets a condition ("provided that").

In spoken German, is it possible to split hiermit into two words?