Sorry for my English as it's not my native language. I'm trying to give You the general idea of where each key/safe is located. This is the order in which I got them.
1. Safe is right above the knife You pick up from the table (its where You meet Your first enemy), the key lies on the tables few steps forward in this room on the table to your left across the switchbox.
2. (as you enter the next room you can see two enemies talking trough a ‘window’ the next key is located in box to the right where the enemy behind the window is standing). In order to get to the key, after the enemies start walking, you need to hug the wall in the shadow and go all the way to the end where a lamp is, go through the small ‘window’ and get your key. The safe is on a table in the next room just before 2 heavy guards.
3. The key is located in the room with the scaffoldings/firing range behind a big white box at on the bottom floor. The safe is located under the stairs on the same floor.
4. The next key is in the same area as previous one. You need to go upstairs and go all the way to your left, there you’ll find a orange box hanging on the wall. To the left of the box with the key is a yellow box with a lever, pull it to open door to a room on the opposite side of scaffolding in which you’ll find the safe.
5. The next key is in one of the small shacks located in the area with the toxic water. The key is hanging on a cooking pan. The safe is located exactly in a shack above the key.
6. In the same area as the previous one except this one is on the other side of the bridge (on your way out of this area) in a shack on a table. The safe is in a small shack to the right of the exit to the next area.
7. After you exit to the next area you’ll find yourself on stairs, simply go down the stairs and find a orange box on the wall, inside there’s a key. The safe is located in a small locked room after you cross a small area with water and generator at the bottom. Simply use your ‘hand charger’ to power up the cell gate controls located on the wall next to the room.
8. After entering the next area on your left there will be a big area with many enemies and water and to the right you’ll find a small room with the key hanging on a railing. The safe is located at the end of this area after you go through closed door to your left.