Learn Spanish (Latin America): De revisar la turbina, ustedes usarán el casco correcto. - If inspecting the turbine, you will use the correct helmet.

Using de followed by an infinitive is a stylized, often formal way to set up a conditional statement. It means the exact same thing as using si (if) plus a conjugated verb. In this case, de revisar is just an alternative way to say si ustedes revisan (if you all inspect).

Since revisar is an infinitive, how do we know who is doing the inspecting?

When you use the de + infinitive structure, the person performing the action is assumed to be the same as the subject of the main sentence. Because the second half of the sentence specifies ustedes usarán (you all will use), we naturally understand that ustedes are the ones inspecting the turbine.

Why use the future tense usarán (will use) instead of a direct command like usen (use)?

Just like in English, the future tense in Spanish can be used to express a strong, non-negotiable command or rule. Saying ustedes usarán (you will use) sounds more like an official safety regulation or a strict mandate than a simple request.

How would the meaning change if the sentence used the perfect infinitive (de haber revisado)?