Nations stockpiling sarin have tried to overcome the problem of its short shelf life in three ways. One way is to lengthen the shelf life of unitary (pure) sarin by increasing the purity of the precursor and intermediate chemicals and refining the production process. Another way to increase shelf life is by incorporating a stabilizer chemical. Initially used was tributylamine, but later this was replaced by diisopropylcarbodiimide (DIC), which allowed for sarin to be stored in aluminum casings. Finally, stockpiling of sarin can be improved by developing binary chemical weapons, where the two precursor chemicals are stored separately in the same shell, and mixed to form the agent immediately before or when the shell is in flight. This approach has the dual benefit of making the issue of shelf life irrelevant and greatly increasing the safety of sarin munitions. However, experts do not put the shelf life of this type of weapon past 5 years.