This achievement is earned by killing 30 enemies with explosive crates. Kills made with Volatile Test Tubes do not count towards this.
There are numerous parts of the game with explosive crates. A good place to work on this is in Act 3. Just after you pull the lever to open the door and activate the slicers, you enter a room with several red crates, a stairway, and three enemies in the room. You can try getting enemies from the previous room to follow you. Lure the enemies near the crates, then attack the crates, causing them to explode, killing the enemies nearby and very likely you. Repeat until you unlock the achievement.