Credit to soliunasm at X360A.org
Chapter 1 - This one is mandatory. It's the tutorial on how to shut the decompression off, and you get one kill for free.
Chapter 3 - Right at the beginning you get your first area you can decompress stuff. You get attacked by one of those bombing guys(With the orange exploding sack on their left arm), two children, and one normal Necromorph. Ignore these four. Kill them but do not hit the glass in back. Then, run up to the glass and you should be attacked by five kids. Kite them all until you can see all five of them in front of you(You should go back to the entrance of Chapter 3, the elevator) and then shoot the glass. You get five kills here for a total of six overall.
Chapter 4 - In the Unitologist Indoctrination room, right after you fix the fuses to allow you to enter the other room, you get attacked by three Necromorphs one you leave the fuse room, so once the three pop out, destroy the window in front of you and now you have a total of nine overall.
Chapter 7 - This is the area with the rogue AI. I can't remember where it is, but once you enter the center of the room you get barricaded in by two Detonator Mines and some explosive barrels at the end of those mines, so you are unable to move them. You can move the explosive barrels at the end prior to the mines being triggered though, then you can shoot out the window yourself and get about 6 kills from all the explosive babies.
Chapter 9 - This is the last one. After you kill the Divider and proceed into the next room, there should be a Power Node on the right. Go to that and you will have a Black Necromorph drop on you and an exploder on the right walking toward you. Shoot out the window directly in front of you.