Photothermographic thermal processor filtration system

A thermal developing unit for the thermal development of photothermographic media which comprises a means for thermally developing photothermographic media by placing said media in contact with a heated element within a case, a first and second opening for venting gas from said case, said first opening being connected to an area surrounding said heated element said second opening being connected to an area within said unit where said media passes after it has been thermally developed, and in a path by which said gas can be vented through at least one of said first or second openings from said case there is a filter cartridge comprising a filter housing containing a chemical filtration media having no bonded absorbent partculates therein.