H2O2 decomposition is highly exothermic (23.44 kcal/mole). Even 10% H2O2 can boil if it becomes grossly contaminated.
The effect of temperature is such that an increase of 10 °C increases the rate of decomposition by a factor of 2.3 (i.e., a first order rate equation). Therefore, decomposition can accelerate if the solution becomes grossly contaminated.
As the concentration of H2O2 in solution increases, there is less water to absorb the heat of decomposition. A crossover occurs at 63-64% H2O2 where rapid, accelerated decomposition becomes self-sustaining and the concentration of H2O2 in the decomposing solution can actually increase.