The Model 851 Investigator`s Aid is a rugged, calibrated detector which detects the presence of hydrocarbons/accelerants/gases that may be present at a fire scene. It is equally effective as a general purpose gas detector. It incorporates advanced signal processing techniques and features two modes of operation: a high sensitivity search mode for locating very small gas leaks, and a calibrated mode that indicates 0% to 100% of the lower explosive limit (methane is test gas). In addition to its uses in the arson investigation field, the Model 851 is an excellent tool for use in detecting Methane Outgassing, Leaking Underground Storage Tanks, Hazardous Materials and Petrochemicals.