An experimental study of the flammability properties of PMMA at low pressures and oxygen concentrations was performed. The work was motivated by the importance of these effects on fire safety in the aviation industry. Measurements were obtained in a mass loss calorimeter inside a large 10 m(3) pressure vessel capable of reaching pressures as low as 0.1 atm. The PMMA flammability was characterized by measuring the burning rate and the time to ignition of small test samples. These were ignited and burned under different external heat fluxes, total pressures and oxygen concentrations. The combined effects of pressure and oxygen concentration on the burning rate, combustion flow field, and ignition were evaluated. Results showed that at low pressure, the burning rate was less intense with a decrease in the mass loss rate. However, the reduction in pressure caused a shortened ignition delay time. Experimental measurements were compared with a simple analytical model showing good agreement. The results also show how pressure and oxygen concentration contributed to the heat transfer from the flame. The model revealed that a single function in oxygen and pressure could account for both flame radiative and convective effects. As a result, a power law fit was obtained for the relation of the combined pressure and oxygen effect on the burning rate. This correlation shows a good agreement with the measurements and predicts the burning rate behavior for the full range of pressure and oxygen tests. (C) 2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved.