Ann Marie Bailey University of Virginia, 4040 Lewis and Clark Drive, Charlottesville, VA 22911 e-mail: amb9um@virginia.edu John J. Christopher University of Virginia, 4040 Lewis and Clark Drive, Charlottesville, VA 22911 e-mail: jjc2c@virginia.edu Robert S. Salzar University of Virginia, 4040 Lewis and Clark Drive, Charlottesville, VA 22911 e-mail: rss2t@virginia.edu Frederick Brozoski United States Army Aeromedical Research Lab, Fort Rucker, AL 36362 e-mail: frederick.brozoski@us.army.mil Comparison of Hybrid-Ill and Postmortem Human Surrogate Response to Simulated Underbody Blast Loading Response of the human body to high-rate vertical loading, such as military vehicle under body blast (UBB), is not well understood because of the chaotic nature of such events. The purpose of this research was to compare the response of postmortem human surro gates (PMHS) and the Hybrid-Ill anthropomorphic test device (ATD) to simulated UBB loading ranging from 100 to 860 g seat and floor acceleration. Data from 13 whole body PMHS tests were used to create response corridors for vertical loading conditions for the pelvis, Tl, head, femur, and tibia; these responses were compared to Hybrid-Ill responses under matched loading conditions. [DOI: 10.1115/1.4029981J Introduction Despite the availability of automotive-rate data collected for the purpose of determining the response of the human [1^4], there is lit tle information on the response of the seated human to vertical load ing scenarios at high rates, such as those experienced during an UBB. While injuries due to UBB loads were discussed in a previous work [5], this paper will characterize the subsequent response of the human using biofidelity response corridors, as well as compare the response of the PMHS to the Hybrid-Ill ATD. A great deal of biomechanical knowledge currently exists for the lower extremities [1^4] and pelvis [6-11], but a majority of this data is limited to automotive rates. The existing literature pro vides data from lower loading rates and has not included personal protective equipment such as boots and used boundary conditions which make comparing to UBB conditions difficult. Understand ing how results from these previous studies relate to responses from UBB-like loading remains an important goal for this and future studies. While antipersonnel landmine blast studies such as Bass et al. in 2004 performed tests on PMHS and surrogate limbs exposed to C4 landmine blasts, the loading conditions involved direct expo sure to the conflagration and are not as well defined as a high-rate impact tests [12]. Because of this, these results are difficult to compare to UBB conditions and do not provide insight into the response of the whole body. Similarly, component lower extrem ity tests, such as those performed by McKay and Bir [13] and Quenneville et al. [14], provide some information about injuries from higher rate axial loading conditions; however, the boundary conditions of these tests may prove insufficient for examining the kinematic response of the legs and may inaccurately represent the mass recruited at these high rates. Characterization of how the higher loading rates of UBB affect the response of the lower limb and pelvis in situ will provide valuable information toward Manuscript received August 6, 2014; final manuscript received February 24, 2015; published online March 18, 2015. Assoc. Editor: Brian D. Stemper. This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited. understanding the relevant injury mechanisms in UBB events and is essential in the process of developing biofidelic ATDs. This paper presents analysis on the response of a human passen ger to a vertical load delivered through the seat and floor to a human passenger. Though various component PMHS tests have been performed for vertical loading scenarios [7,12-14], this study aims to compare whole body PMHS and Hybrid-Ill ATD response to laboratory-simulated UBB events. Data and analysis in this paper supplement whole body simulated UBB test results presented in a previous work [5], while presenting preliminary response corridors for PMHS and ATD occupants under these high rate loads, with particular attention to the lower extremities and pelvis. Experimental Methods The University of Virginia’s Odyssey blast rig [5] was used to perform a total of ten whole body Hybrid-Ill ATD tests and 13 whole body PMHS tests using eight specimens with an average specimen age of 64.3 ± 3.5 yr, mass of 88.7 ± 14.9 kg, and stature of 177.8 ±4. lcm (Table 1). Fresh-frozen PMHS were obtained through the Virginia State Anatomical Board and other approved tissue suppliers and screened for Hepatitis A, B, C, and Human Immunodeficiency Vims (HIV). The University of Virginia Cadaver Use Committee approved all protocols. Pretest computed tomography (CT) and femoral neck bone mineral density scans were performed on each test specimen to ensure no pre-existing fractures were present and that the bone mineral density fell within ±2.5 standard deviations of the average bone mineral den sity of a 30yrold male [15]. The ODYSSEY blast rig, described in a previous work [5], used a hammer sled to impact the seat and floor pan of a carriage sled holding the specimen in a supine, seated position (Fig. 1), to simulate the positive and negative phase accelerations of UBB events [16,17] (see Fig. 2). Pulse shapers consisted of 40- and 60- durometer polyurethane blocks mounted to the impacting surface of the seat and floor pans, while velocity of the hammer sled was controlled by a Via Systems Model 713 pneumatic sled (Via Sys tems, Brighton, MI). Journal of Biomechanical Engineering MAY 2015, Vol. 137 / 051009-1