This document provides principles for characterizing the measured production of toxic gases from a laboratory fire test and provides bases for comparing the results between different types and scales of such tests. It also includes consideration of the uncertainties in the gas determinations. The combined uncertainty is a key factor in the ability to establish similarity or difference of test results.The sufficiency of the agreement between a bench-scale test and a real-scale test depends on the precision needed in the fire hazard or risk assessment, which is not covered by this document.This document defines the relevance and significance of toxic gas data from measurements in different fire tests. With such a definition it is possible to provide generic guidance on how such data can be compared between different sizes and types of fire tests.The combustion conditions represented by the fire test, other specific characteristics of the test and the test specimen, the sampling strategy of the fire effluents, and the analysis technique for the toxic gas species are the most important factors when defining the significance of the toxic gas data.This document is intended to serve as a tool for the definition of the relevance and significance of toxic gas data from fire tests, comparison of toxic gas data from fire tests of different scales and characteristics, and prediction of toxic gas data from a large-scale test based on small-scale data or vice versa. This document gives general guidance regarding comparison of toxic gas data between physical fire models of different scales, but is principally developed for the gases listed in ISO13571, i.e. carbon dioxide (CO2), carbon monoxide (CO), hydrogen halides (HCl, HBr, HF), sulfur dioxide (SO2), hydrogen cyanide (HCN), nitrogen oxides (NO, NO2), formaldehyde (CH2O) and acrolein (C3H4O).This document is not applicable to characterization and comparisons of the toxicity of the effluents from fire tests.