Throughout Kazakh there are large canisters dotted throughout the landscape. They grant a large boost of health when smashed and are green in colour. These collectibles appear on your map as large green ovals. There are many throughout the game. A general tip is when you are mopping up and going for your collectibles, if you uncover the fog of war in all corridors on each screen then you won't have missed once as none of these are truly hidden away. There are two important things to note with regards to the canisters :
1) There are six/eight (need confirmation) located in the Balrog level. If you uncover all the map, you won't miss any. Be warned, as once you exit the Balrog level it is impossible to return, making this achievement one of two that is 'truly' missable.
2) There are eight canisters after the point of no return located in Meio's tower, so don't worry if you're scouring through the map but your achievement hasn't popped.
NOTE - Some members are claiming they missed canisters located on the Balrog but still got their achievement. Waiting for confirmation on if these count.