Don't play through this game twice if you're simply trying to get this achievement. If you are playing through on a different difficulty then do that and shoot the few you notice, but if you're limited on time and just want this achievement, this is what I did.
Choose the second level on the easiest difficulty. Quickly hide behind something as three guys will run at you. Kill all three. Next we are going to group two achievements together, this one and the "say no to pots" - shoot potted plants. You'll notice there are potted plants hanging out on top of the stuff, including a couple in the corners. To destroy them you have to shoot them so you actually phsyically hear a break and you see a crack in the pot.
Now, move forward. There will be two guys shooting at you. Ignore them. Shoot the three fire extinguishers in the room. You can't miss them, I promise. Let the two guys kill you, which will restart the level. This will prevent you from actually having to physically restart the level, saving some loading time.
Rinse and repeat 10 times if you somehow didn't shoot a single fire extinguisher throughout the whole game. Probably more like 6 times.