The short answer is that I don’t know the shelf life of chemical weapons, but please read on.
According to Wikipedia, Sarin has a very short shelf-life of only a few weeks to a few months but can be extended up to five years with advanced chemistry and that the “production and stockpiling of sarin was outlawed as of April 1997 by the Chemical Weapons Convention of 1993”
However, this doesn’t align with other information that I have. I live near the Blue Grass Army Depot in Central Kentucky which is constructing a chemical destruction facility so that the chemical weapons stored there can be destroyed on site. This is a major construction project. “Groundbreaking for the chemical destruction facility took place on October 28, 2006. Final design of the facilities should be complete in 2010 and actual construction in 2018, after which destruction of the weapons will begin.” BTW, none of this 12 year construction project is visible from the roads that surround the Depot.
So if it’s true that Sarin was last produced in the U.S. in 1997 and has a maximum shelf life of 5 years, then the stuff should have deteriorated down to nothing by 2002. So why begin a major construction project in 2006 that won’t even be ready to operate until 2018, 16 years past the date of the end of production plus the stated shelf-life?
Something doesn’t add up but the construction project tells me that the shelf life is much longer than 5 years.
I wonder if, as another freeper described it on another thread, many of these chemicals are “binary” - that is, 2 stable compounds with a long shelf life are stored separately, then mixed when the resultant agent is desired. The images on another thread of 2-sided containers lends to that possibility.
So, the gas could have a short shelf life, but the compounds that, when mixed, create the toxic gas are more stable.