Thermal imaging cameras are rapidly becoming integral equipment for first responders for use in structure fires and other emergencies. Currently there are no standardized performance metrics or test methods available to the users and manufacturers of these instruments. The Building and Fire Research Laboratory (BFRL) at the National Institute of Standards and Technology is conducting research to establish test conditions that best represent the environment in which these cameras are used. First responders may use thermal imagers for field operations ranging from fire attack and search/rescue in burning structures, to hot spot detection in overhaul activities, to detecting the location of hazardous materials. In order to develop standardized performance metrics and test methods that capture the harsh environment in which these cameras may be used, information has been collected from the literature, and from full-scale tests that have been conducted at BFRL. Initial experimental work has focused on temperature extremes and the presence of obscuring media such as smoke. In full-scale tests, thermal imagers viewed a target through smoke, dust, and steam, with and without flames in the field of view. The fuels tested were hydrocarbons (methanol, heptane, propylene, toluene), wood, upholstered cushions, and carpeting with padding. Gas temperatures, CO, CO2, and O2 volume fraction, emission spectra, and smoke concentrations were measured. Simple thermal bar targets and a heated mannequin fitted in firefighter gear were used as targets. The imagers were placed at three distances from the targets, ranging from 3 m to 12 m.