Estimating Brain Injury Risk from Shipborne Underwater Blasts Using a High-fidelity Finite Element Head Model
Authors: Nakarmi Sushan , Wang Yaohui , Fawzi Alice Lux , Franck Christian , Carlsen Rika Wright 
Published: June 2024

ABSTRACT

Introduction
Assessing the survivability of, and potential injury to, a ship’s crew from underwater blast is crucial to understanding the operating capability of a military vessel following blast exposure. One form of injury that can occur and affect a crew member’s ability to perform tasks is traumatic brain injury (TBI). To evaluate the risk of TBI from underwater blasts, injury metrics based on linear head acceleration have traditionally been used. Although these metrics are popular given their ease of use, they do not provide a direct measure of the tissue-level biomechanical responses that have been shown to cause neuronal injury. Tissue-based metrics of injury, on the other hand, may provide more insight into the potential risk of brain injury. Therefore, in this study, we assess the risk of TBI from underwater blasts using tissue-based measures of injury, such as tissue strain, strain rate, and intracranial pressure, in addition to the more commonly used head acceleration-based injury metrics.

Materials and Methods
A series of computational simulations were performed using a detailed finite element (FE) head model to study how inertial loading of the head from underwater blast events translates to potential injury in the brain. The head kinematics loading conditions for the simulations were obtained directly from Floating Shock Platform (FSP) tests where 3 Anthropomorphic Test Devices (ATDs) were positioned at 3 shipboard locations (desk, bulkhead, and bench), and the head acceleration was directly measured. The effect of the position and orientation of the ATDs and the distance of the underwater blast from the FSP (20–50 ft) on the risk of brain injury were assessed from the FE analysis.

Results
The head accelerations and estimated TBI risk from the underwater blasts highly depend on the positioning of the ATDs on the FSP and decrease in severity as the charge standoff distance is increased. The ATD that was seated at a desk had the largest peak linear head acceleration (77.5 g) and negative intracranial pressure (−51.8 kPa). In contrast, the ATD that was standing at a bulkhead had the largest computed 95th percentile maximum principal strain (19%) and strain rate (25 s−1) in the brain. For all tested conditions, none of the ATDs exceeded the Head Injury Criterion (HIC-15) threshold of 700 for serious or fatal brain injury; however, the predicted tissue strains of the bulkhead ATD at the 20-ft charge standoff distance were within the range of proposed strain thresholds for a 50% risk of concussive injury, which illustrates the added value of considering tissue-level measures in addition to head acceleration when evaluating brain injury risk.

Conclusions
In this work, we assessed the risk of brain injury from underwater blasts using an anatomically detailed subject-specific FE head model. Accurate assessment of the risk of TBI from underwater explosions is important to evaluate the potential injury risk to crew members from underwater blast events, and to guide the development of future injury mitigation strategies to maintain the safety of crew members on military ships.