A dimensionless index was suggested as a measure of flue-gas toxicity, I-tox(t) = [CO]/[CO](permis) + ((4.6/3)[NO] + [NO2])/[ NO2](permis) + Sigma([C-org,C-j]/[C-org,C- j](permis)) + Sigma([C-inorg,C- k]/[C-inorg, k](permis) where [C-org,C- j] and [C-inorg,C- k] are normalized (with respect to fixed O-2, e.g. 11 vol.% in flues) concentrations of jth organic and kth inorganic components, resp., and the permissible concentrations are the lawfully permitted thresholds. The I-tox(t) varies significantly only when any quotient term varies essentially. Paint shop solvent vapors and 1-propanol afterburnt with CO, NO, NO2, and O-2 determined in flue gases, gave I-tox(t) of 740-1013 over 715-770degreesC and 49-15 over 825-860degreesC, resp., e.g., over 715-770degreesC CO fell to 1/7th and NO rose by 56%, showed the temp. raised in the combustion chamber to have had an adverse effect. Methane, 1-propanol and benzene were burnt in a 0.375-043 mm quartz sand fluidized bed at 700-1050degreesC and air excess varied over1.1-2.2 and CO, NOx, CxHy concentrations were recorded (at 11 vol% O-2) and flue-gas toxicity was followed in terms of I-tox(t).