Crossing to the Other Side Achievement Guide
This is where you defeat Liam O'Neal, he's armed with a Flamethrower and around the arena are buttons that turn on the sprinklers
. You will want to press the button every so often as the area will be burning around you meaning that you will not have as much space to move around.
Best strategy I found was to use the Explosive and Smoke Bolts along with the Sniper Rifle and Shotgun.
Hope this helped.