There are no BF keys in barrels that I recall. In act 1 there are 2 level 1 BF keys (one on the ground that you can't miss and the other in a locked chest near the start of the game). The level 2 BF key can be found shortly after you reach the citadel; <span class='standouttext'>Spoiler : </span><span class='spoiler'>it is in the area guarded by DK Patrols, in one of the side rooms hidden behind some packages and crates</span> (highlight the text to read).
AFAIK, there are no keys for locked barrels. You need to use the Lockpick skill to open them. Some people stash locked barrels in the BF until they can boost the skill enough to open them, but they only contain random loot, so you wouldn't be missing anything vital by leaving them behind.
