# Ballistic Head Protection in the Light of Injury Criteria in the Case of the Wz.93 Combat Helmet
## 6 Conclusions  
Based on the analysis of development trends for combat helmets currently used in the largest army in the world (the United States) and the Polish armed forces, it has been concluded that the helmets used for protection purposes in our army are capable of withstanding only the first two threats (see Table 2). In the case of blast explosives, there is a very high risk of the wearer suffering a traumatic brain injury from the acoustic effect of propagation of the free explosion wave. The helmets used in our army correspond to the American Advanced Combat Helmet (ACH) and Future Assault Shell Technology (FAST) programs (2005-2010), which means that they are from three generations ago with helmet electronics and display system (heads-up), and future (ballistic/blast/blunt trauma) or the latest standard intelligent hypersensor processing system (IHPS).  
Nonetheless, based on the obtained results, it can be stated that the analyzed structure is only capable of dealing with a single strike. If hits like those of the multi-hit model were recorded, the standards (\(x_{\mathit{def}}\)) would be exceeded. The obtained dynamic deflection and permanent deflection results did not exceed the limit values (see Table 4). As shown in Figure 11b, the estimated dynamic deflection for shot number three or four could cause serious skull trauma, although other results from the firing were within the tolerance limits of current standards (see Figure 18) [51]. In comparison with data received from the impact machine, dynamic deflection was found to be outside the desired range. The duration of the event was within the required range and (based on [30]) did not exceed 15 m/s. Estimating the depth of the deflection (\(x_{\mathit{BFD}}\)) when determining the BC, where the limit of permanent deflection was estimated to be approximately 7-15 mm [38], the registered deflections (see Figure 18) were on the borderline of skull injury (fracture). Referring to Table 3, the likelihood of injury occurrence is, therefore, AIS 3+ for BC.  
The results presented in this paper were performed on the helmet only, and are burdened with error, future studies should endeavor to estimate headform injuries using standardized equipment. A detailed analysis of changes in the impactor surface (mushroom projectile) is planned as it would be a mistake not to consider increasing the diameter of the surface involved in the process of absorbing impact energy when estimating actual indicators of the BC.  
Figure 18: Estimation of deflection \(x_{\mathit{BFD}}\) as a function of speed from the ballistic test in the light of standards and literature.  
**Author Contributions:** Conceptualization, K.J., M.B. ([PERSON]), and S.P.; Methodology, M.B. ([PERSON]), M.K., R.S., and M.M.; Validation, K.J., and M.K.; Formal Analysis, K.J., M.B. ([PERSON]), and S.P.; Investigation, K.J., R.S., and M.K.; Resources, M.B. ([PERSON]), and M.M.; Data Curation, K.J., M.K.; Writing--Original Draft Preparation, K.J., M.K., and M.B. ([PERSON]); Writing--Review & Editing, M.M., and S.P.; Visualization, M.B. ([PERSON]), and S.P.; Supervision, K.J., and M.B. ([PERSON])  
**Funding:** This research received no external funding.  
**Conflicts of Interest:** The authors declare no conflict of interest.  
**Acronyms and Abbreviations**  
ACH Advanced Combat Helmet  
AIS Abbreviated Injury Scale  
BC blunt criterion  
BFD backface deformation  
ECH Enhanced Combat Helmet  
FAST Future Assault Shell Technology  
FMJ full metal jacket  
HEADS-UP Helmet Electronics and Display System-Upgradeable Protection  
HIC head injury criterion  
IED improvised explosive device  
IHPS integrated head protection system  
NIJ National Institute of Justice  
PASGT Personnel Armor System for Ground Troops  
TBI traumatic brain injury