Abstract: An infrared radiation measuring pyrometer whose output is used to calculate both particle and gas temperatures from an explosion or fire. Preferably four infrared wavelength measurements are made to compute the particle temperature and two infrared wavelength measurements to compute the gas temperature. Especially constructed to operate in an explosion environment, the invention allows the simultaneous and continuous measurements for both particle and gas temperatures. Planck's Law is used to relate the radiation emitted from the particles and/or gas to the wavelengths observed, the emissivity of the object at that wavelength, and the temperature of the particles and/or gas. For each specific wavelength detected at the pyrometer there is an output voltage which can be related to the flame radiation.