The characterization of fire atmospheres is discussed. A complete description would require more than 10¹⁷ measurements. This is beyond present capabilities, but the requirements could be reduced by separating the problem into three regimes, each characterized by a minimum volume-time (v, t) increment. They are: (a) overall fire atmospheres (v = 1 m³, t = 10 s) for hazard and detection, (b) fire plumes (v = 10⁻⁶ m³, t = 10⁻¹ s) for heat transfer and fire propagation, and (c) flames (v = 10⁻¹⁵ m³, t = 10⁻⁴ s) for microscopic and molecular combustion processes. By systematically applying these characterizations to the regions where they are required, the data base can be reduced to 10⁶ measurements for a typical small fire. This is feasible with present technology. However, the application would require a substantial investment in facilities and the development of sampling and analytical technique. Some sampling and analytical problems associated with characterizing fire atmospheres are discussed. The current status is illustrated using several recent studies.