A standard material flammability assessment method, the Microscale Combustion Calorimetry (MCC), was modified and utilized to examine incomplete combustion of gaseous decomposition products of polymeric materials. The incomplete combustion conditions were attained by changing the MCC combustor temperature, oxygen concentration and residence time. A numerical model of the combustor, taking account spatial non-uniformity of its temperature, was developed and employed in inverse modeling mode to derive the global combustion kinetics for polystyrene and poly(butylene terephthalate) and their blends with gas-phase active flame retardant additives. The kinetic parameters were found to be highly sensitive to the presence of these additives. The speed of laminar flame propagating in a stoichiometric mixture of the pyrolyzates and air was estimated from the derived kinetics and proposed as a quantitative measure of gas-phase flame retardant effectiveness. (C) 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.