# Numerical Analysis of EOD Helmet under Blast Load Events Using Human Head Model
## 1 Introduction  
Nowadays, due to armed conflicts and terrorist threats, people injured and killed by explosive devices as weapons represent a significant percentage worldwide. Improvised explosive devices (IEDs) are the leading cause of death among Western troops on missions in conflict zones. IEDs have caused, for example, some 312,000 mild traumatic brain injuries (mTBI) among the US military between 2000 and 2018 [1]. The use of explosive weapons in conflict scenarios has to lead to the need of protecting troops from blast explosions, particularly the bomb squad, whose specialty is handling explosives. First personal protection equipment appeared in the First World War and has evolved to the modern suits worn by the explosive deactivation technicians or EOD (explosive ordnance disposal) suits. The analysis of combat helmets, usually ACH (Advanced Combat Helmet) or similar, has been done for ballistic threats using international standards such as STANAG 2920 [2] or NIJ 0106 [3]. These studies vary from the analysis of the mechanical behavior of the helmet to the analysis of brain injuries. Regarding the analysis of combat helmets subjected to blast waves, very few studies are found, and these are mostly performed on the same ACH combat helmet. The first few relevant studies on the analysis of blast-induced traumatic brain injury (bTBI) in users of military combat helmets were published around 2010 [4; 5; 6; 7; 8]. [PERSON] et al. [9] analyzed the attenuation capacity of an explosive wave in an ACH helmet. They have developed a finite element model in the LS-Dyna(r) software to evaluate the actions on thehead, with and without the combat helmet. They have used four levels of overpressure of [PERSON]'s lung damage threshold curves, between 0.27 and 0.66 MPa; also analyzing the influence of head orientation. The modeled head has been previously validated with Intracranial Pressure (ICP) measurements on corpses in shock tube experiments. They concluded that the presence of the ACH helmet attenuates the explosive wave in comparison to the unprotected case/situation: the stress in the head and on the cranial cavity and the general ICP levels (Intracranial Pressure) are reduced. Moreover, a fraction of the impact energy is absorbed by the compression of the helmet-pads; meanwhile, a part is transmitted directly to the head but to a lesser extent than without a helmet. [PERSON] et al. [10] used a Finite Element Method (FEM) model in the ABAQUS software to analyze the effect of a fully covered ACH helmet, that is, a visor and a jaw guard have been added as complements to improve its effectiveness. They concluded that the presence of additional protective equipment reduces maximum pressures in the brain (ICP) by up to 5 times, and this guarantees that no skull fracture occurs. The underwash effect of military helmets as a mechanism for blast-induced traumatic brain injury has also been studied by different authors [11; 12; 13; 14]. [PERSON] et al. [15] have developed a virtual model of finite elements of a human head and a helmet in order to help in the design of the next generations of helmets for ballistic and explosion protection. They carried out simulations of the head (with and without the helmet) under explosion using a Eurelian-Lagrangian approach and using the CoBi-FEM code to simulate the problem. The model has been validated with experimental tests in shock tubes and focuses on defining possible transmission paths of the energy of the blast wave. [PERSON] et al. [16] analyzed numerically the performance of face shields of a polycarbonate-aerogel composite with ACH helmet subjected to different blast loadings. The use of aerogel showed better protection capability than the classical polycarbonate face shields. Recently, [PERSON] et al. (2020) carried out an experimental and numerical study to obtain the overpressure on the head in different blast wave directions. They used an ACH helmet without complements to protect the face.