Does mustard gas have an “expiration” date. Would mustard gas manufactured years ago be effective today?
"One of the more frequently-dumped weapons was the "Sprühbüchse 37" (SprüBü37, Spray Can 37, 1937 being the year of its fielding with the German Army). These weapons contain sulfur mustard mixed with a thickener, which gives it a tar-like viscosity. When the content of the SprüBü37 comes in contact with water, only the sulfur mustard in the outer layers of the lumps of viscous mustard hydrolyzes, leaving behind amber-colored residues that still contain most of the active sulfur mustard. On mechanically breaking these lumps, e.g., with the drag board of a fishing net or by the human hand, the enclosed sulfur mustard is still as active as it had been at the time the weapon was dumped. These lumps, when washed ashore, can be mistaken for amber, which can lead to severe health problems."
https://en.wikipedia.org/wiki/Sulfur_mustard
Could be a few weeks to a few months. Needs dry storage.