There are a number of aspects that you need to take into consideration.
- you could try immersing the bag in a bell jar full of water and creating a vacuum. if the bags leak, then their not sealed.
- Visual checks of the seal
- you don't say if the bags are gas flushed. if so just measure the level of oxygen in the bag ( mind this could indicate a problem with your gas flush)
- As Tony says, you need to risk assess your process. Unfortunately that something YOU need to do, but he's given you some very good pointers above.