If you can prove full body exposure to Mustard gas - either sulfur or nitrogen, or Lewisite while on active duty, you may be eligible for presumptive disability.  There are certain locations in both the Army and Navy where exposure qualifies for a service connection.

There are 14 conditions that qualify for presumptive disability under Mustard Gas Exposure, and 5 Conditions that qualify.  If you can prove exposure during your time of service in any of the locations with any of the conditions, it becomes much easier to qualify for Disability.