The invention relates to gas generating compositions for use in safety devices for vehicles. In particular, the invention relates to said compositions based on guanidine nitrate used in pedestrian protection devices. The composition substantially comprises 75 to 98% by weight of guanidine nitrate as fuel and 2 to 25% by weight of a burn accelerator selected from the group of the transition metal compounds, the metal nitrates, metal chlorates, metal perchlorates, ammonium perchlorate and mixtures thereof, wherein the transition metal compounds are selected from the compounds of the transition metals Ti, Cr, Mn, Fe, Cu, Zn, Zr and Mo and wherein the gas generating composition exhibits a burn rate of from 3 to 17 mm/s at 20 MPa.