Why does heating an aerosol can cause it to explode?

An aerosol can is pressure vessel, that is the contents are at a higher pressure than the atmosphere. As such it is deigned to contain pressures up to a certain point. As it is heated the pressure increases because of the ratio of P=VT until the mechanical strength of the can is exceeded. It then ruptures (not explodes) allowing the contained material to expand. If the contents are a flammable liquid they may become a BLEVE or fireball of deflagrating material. Again this is not an explosion.