Copper Mill - Multi-Level Building with Flammable Gas Leaks (Part 1)

As you enter this room Lara spots, 3 Trinity soldiers attempting to crack a safe. If you're quiet and stay hidden behind the rusty mine cart so they don't notice you, you can then shoot the generator behind them to cause an explosion that should kill one or two of them. Then finish off any survivors.

You could also toss a molotov into the pool of gasoline behind them to burn them and the surrounding storage crates.

Or, use a single poison arrow to take out all of them, but I recommend saving at least 3 poison arrows for the final enemies in this area

Once they're dead, toss another molotov at the cosmonaut poster (7/7) on the upper level to destroy it for the Difference of Opinion Challenge. If you've burned the other posters as well, you'll receive XP and Expedition Credits for your efforts.

NOTE: If you return here later in the game, there are no more bottles to make molotovs. So don't bother coming back until you've unlocked FIRE ARROWS or you'll just waste your time.

Search the bodies and gather other ammo and supplies. Then craft another molotov and use it to destroy the flammable barrier blocking the hallway to the northeast. The decaying wooden building begins to burn, making your escape a bit more challenging.

As you move along the hallway, pick up more rifle ammo, and get ready to meet more enemies just around the corner.

In the heat of combat it's easy to miss the brief tutorial about gas leaks. When you see a pipe wrapped in red tape, with vapor leaking out of it, you can add fire—by throwing a molotov or shooting the hanging lanterns—to cause an explosion, injuring nearby enemies. Lara can also be hurt if she's standing too close. But of course, you can also kill these 4 guys with regular weapons if you prefer.

Move through this room, picking up ammo and magnesite and looting bodies as you go. Then go up the stairs to the next level.