The object of the research are explosive properties of the pyrotechnic composite consist of fine grade magnesium-aluminium powder (PAM) and highly dispersed polytetrafluorethylene (PTFE). The composite reveals high resistance to all mechanical and thermal impulses and is extremely sensitive to hot sparks and open fire. The burning rate of the composition changes from 1 cm·s^-1 to 100 m·s^-1 along with decreasing its density. Charges of the composition with density below 1 g·cm^-3 burn so violently, that the phenomena is similar to explosion. Charges with density above 1.1 g·cm^-3 burn relatively rapidly and stably. The main part of the paper concerns the pressure impulses in the air generated during high-rate burning of the composition of bulk density. The nature of the generated pressure impulse is not that of a typical shock wave. A rise of pressure over the distance from the point of explosion to the maximum value lasts 50-100 milliseconds, while for shock waves this factor is less than a microsecond for equivalent charges. The methods of initiation of the composition influence the shape and parameters of the pressure impulse. The explanation of the nature of great changes of the composition burning rate has been proposed. The effect described in the paper was used for evaluation of explosive pressure resistance of industrial doors and windows.