12 A new optical tool, which will help petrochemical refinery and chemical processing plant personnel locate the source of a toxic or hazardous gas leak while remaining outside the perimeter of the processing area, has been demonstrated. This sensor is capable of locating leaks from a distance of about 20 m, with a response time of less than 1 second. By enhancing the speed with which leaks can be located, the risk of an incipient failure becoming a catastrophic failure is reduced significantly. The tool is based on Tunable Diode Laser Absorption Spectroscopy (TDLAS). TDLAS is currently being utilized in these industrial environments in permanently-installed open-path configurations to sense releases of selected gases as they exit the processing area. The sensor described here combines a lightweight, portable optical transceiver with battery-operated electronics in a single hand-held package. By standing in a safe area and `shining' the eye-safe laser beam emanating from this device onto suspected leak sources, operators may rapidly isolate the source while minimizing their potential exposure to the hazard. The sensor can be configured to sense leaks resulting in path-integrated concentrations of, for example, 2 ppm-m of hydrogen fluoride, 200 ppm-m of hydrogen sulfide, or 10 ppm-m of methane.