Predictive tools and experiments for blood backspatter: incorporating tissue simulants and muzzle gas interactions

The proposed project is an integrated modeling and experimental effort to improve the state of forensic bloodstain pattern analysis (BPA). Significant advances in modeling aim to incorporate the role of recently observed behavior for the formation (atomization) of liquid blood drops from (1) sheet breakup and (2) flow-induced breakup. Both of these mechanisms are expected to significantly alter the blood droplet size distribution, which will lead to cascading effects in the flight of these drops through air, and their ultimate formation of bloodstains when landing on surfaces. The models will improve upon current state-of-the-art knowledge, and provide a predictive capability incorporating the significant effects of muzzle gases at close- to mediumrange. Such predictive capability will provide the first quantitative comparison and validation with corresponding experimental bloodstain pattern and in-flight droplet measurements. The proposed effort will also examine the role of biological simulant materials in the production of backspatter. A direct comparison between postmortem pig brains and a series of cranial backspatter simulant materials will provide a guide for use of biological simulants in backspatter BPA testing. Configurations with biological simulant materials will be compared to a prior configuration using a simple blood cavity to directly establish the key mechanisms for production of bloodstain pattern material (tissue and blood). High-speed imaging measurements will provide for detailed measurements of the timescales of backspatter formation, flight, and allow for direct comparison with sampled bloodstain patterns. Finally, the high degree of variation in these complex interacting physical phenomena (blood atomization, interaction with turbulent muzzle gas jets, and biological variation) will be considered through comprehensive experimental datasets designed to establish the repeatability and variance in both simple blood cavity and simulated cranial backspatter configurations.