In recent years, casualties due to the impacts of falling lapilli and ballistic ejecta resulting from volcanic eruptions with unclear precursors have increased. However, while research and development efforts aimed at protecting people from such scattered ejecta via improved volcanic shelters are progressing, there has been little research on volcanic disaster prevention measures aimed at directly protecting the human body. Accordingly, this study reports on the development of an impact test apparatus and a human head model that can be used to evaluate the impacts of volcanic lapilli as well as the results of our impact resistance evaluation of a commercially available mountaineering helmet (ravina FLUQUE made by Tanizawa Seisakusho, Ltd.). In our experiments, vitrified grindstone with a standard density of approximately 2400 kg/m3 were used as simulated lapilli and launched at the helmet at velocities of approximately 40-80 m/s. Impact safety was evaluated from the damage sustained by the helmet and the head injury criterion (HIC) value, which was calculated via a triaxial accelerometer installed on the head model. Experimental results show that the damage to mountaineering helmet used in this study was small and that the HIC value was low even when it was impacted by lapilli equivalents with diameters up to 30 mm travelling at velocities of up to approximately 60 m/s, thereby suggesting that the mountaineering helmet provided sufficient protection up to that impact velocity. Additionally, summarizing the relationship between the interior/exterior damage of the helmet and the HIC value, it was found that the HIC values can vary significantly due to deformation and fracture of the protective foam material mounted inside the helmet.
