There are multiple Geneva Conventions, true. One of them deals with POWs. Other Conventions deal with other war-related topics. If you want to be technical abou

There are multiple Geneva Conventions, true. One of them deals with POWs. Other Conventions deal with other war-related topics. If you want to be technical about it, the one prohibiting the use of gas is formally known as the Geneva Protocol. I linked to the CWC because that is the relevant international convention allowing for the use of tear gas in non-military contexts. IOW, the GP creates the ban, but the CWC provides an exception.)