# Numerical Analysis of EOD Helmet under Blast Load Events Using Human Head Model
## 3 Results and Discussion
### Cerebrospinal Fluid Pressure  
The analysis of the pressure in the cerebrospinal fluid due to the action of external loads allows us to know the degree of injury suffered. This criterion was formulated by [PERSON] et al. [55] and related the cavitation in the cerebrospinal fluid with the probability of suffering a subdural hematoma. According to Reference [55], three pressure levels are differentiated, each related to the probability of suffering brain damage:  
* For pressures, lower than \(-\)94 kPa, there is a 5% probability of subdural hematoma.
* For pressures between \(-\)94 kPa and \(-\)134 kPa, the probability increases to 50%.
* And, finally, when pressure is between \(-\)134 kPa and \(-\)177 kPa, the probability of subdural hematoma increases to 95%.  
The pressure in cerebrospinal fluid shows that the area with a higher probability of suffering a subdural hematoma injury is located between the cerebellum and the lower temporal and occipital lobes (in Figure 13, this area is bounded by letters A, B, and C) and the middle occipital lone  
Figure 12: Intracranial pressure evolution with and without helmet for the blast loads of 0.050, 0.075, and 0.100 kg.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Case** & **TNT [kg]** & **Intracranial Pressure Peak [kPa]** & **Time [ms]** \\ \hline \multirow{3}{*}{Without Helmet} & 0.050 & 282.8 & 1.74 \\  & 0.075 & 418.6 & 1.66 \\  & 0.100 & 540.6 & 1.54 \\ \hline \multirow{3}{*}{With Helmet} & 0.050 & 80.2 & 4.40 \\  & 0.075 & 121.7 & 4.28 \\ \cline{1-1}  & 0.100 & 150.2 & 4.04 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Maximum intracranial pressure and time in when it occurs for both cases studied.  
(location D). Although there is also a risk of injury in zone E, the probability of injury is reduced to 50% (pressure between \(-94\) and \(-135\) kPa).  
Figure 13 shows the evolution of the pressure in the cerebrospinal fluid during the simulation. This pressure has been calculated as an average of the ABC areas since they are the most critical areas for damage. It has been observed that the calculated average value is slightly lower than point pressure peaks in each of the zones. This assumption is acceptable since, for the evaluation of the criterion, it is a more conservative position.  
In addition, the pressure value is reduced and does not reach \(-94\) kPa in D and E areas, so no injury is observed wearing helmet in these brain locations.  
Figure 13, and more detailed in Table 9, show a reduction in the peaks pressure of these critical areas due to the presence of the helmet: \(28.40\%\) for the \(0.050\) kg load, \(29.95\%\) for the \(0.075\) kg of TNT, and finally a reduction \(31.56\%\) for the maximum explosive load studied, \(0.100\) kg. A reduction of around \(30\%\) of the pressure in these areas is observed due to the action of the protective helmet for the cases studied.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Case** & **TNT [kg]** & **Cerebrospinal Fluid Press [kPa]** & **Time [ms]** \\ \hline \multirow{3}{*}{Without Helmet} & 0.050 & \(-151.73\) & 1.78 \\  & 0.075 & \(-163.30\) & 1.66 \\  & 0.100 & \(-170.03\) & 1.58 \\ \hline \multirow{3}{*}{With Helmet} & 0.050 & \(-108.64\) & 4.28 \\  & 0.075 & \(-114.39\) & 4.12 \\ \cline{1-1}  & 0.100 & \(-116.37\) & 3.88 \\ \hline \hline \end{tabular}
\end{table}
Table 9: Maximum cerebrospinal fluid pressure for both cases studied, with/without helmet.  
Figure 13: Cerebrospinal fluid pressure evolution comparison for all cases studied.