While tripping out of the hole and after an aborted attempt to download an MWD tool, two crewmembers were exposed to what is believed to have been acid from a Lithium/Thionyl Chloride Battery. The MWD engineer had opened a download port in the tool (see photo) in order to download tool memory and found it to be slowly leaking drilling fluid. After unsuccessful attempts to reinstall the plug back in the port, the tool was raised 20 feet and a second port was used. While the tool was being downloaded, a “mist/gas” was observed escaping from the original top port. The affected employees were approximately 15 feet from the rotary table and suffered severe vomiting and shortness of breath.