Recent military conflicts in Iraq and Afghanistan have resulted in an increase in the number of blast related traumatic brain injuries (blast-TBI). It is assumed that the primary mechanism for blast-TBI is the interaction between the blast pressure wave and the central nervous system, but the details of this mechanism are poorly understood. The conditions of such blast injuries are highly variable, and the presence or absence of protective devices such as vehicles or helmets is presumed to have a strong influence on pressure waves. Because of the complexity of this problem and the difficulty of in situ measurement of these effects in actual combat scenarios, one approach is to develop efficient numerical simulations that have the fidelity to reliably model the interaction of the brain and the pressure and shear waves. Here we examine the distribution of pressures and principal strains (stretches) in a brain impinged upon by a blast wave incident from orthogonal directions as simulated by a finite element coupled fluid-solid dynamic interaction framework. We assess the various sources of errors in finite element simulations of wave propagating through tissue, the modeling error, the discretization error, and the error of input parameters (data uncertainty). We conclude that the least important source of error is the assumption of linear kinematics and linear constitutive equation. The discretization error is significant, and controlling it will remain a challenge. The most significant source of error is found to be the input parameter uncertainty (experimental variability) and lack of knowledge of the detailed mechanics of deformation of the brain tissues under conditions of blast loading.