There are some structures in which changes consistent with primary blast may be found despite secondary and tertiary blast being the most frequent sources of injury. The Central Nervous System for example, especially the brain, is well protected yet there are historical and experimental accounts of damage which cannot be attributed to secondary or tertiary blast or even air embolism resulting from pulmonary disruption. Similarly, analysis and experimental simulation of specific skeletal injuries has shown that primary blast alone can fracture bones and that it is likely to be responsible for limb avulsions in victims exposed to stress waves of sufficiently high intensity.