Reply to Response to Vacuous standards - Subversion of the OSAC standards-development process.

This Letter to the Editor is a reply to Mohammed et al. (2021) https://doi.org/10.1016/j.fsisyn.2021.100145, which in turn is a response to Morrison et al. (2020) "Vacuous standards - subversion of the OSAC standards-development process" https://doi.org/10.1016/j.fsisyn.2020.06.005.

Vacuous standards - Subversion of the OSAC standards-development process.

In the context of development of standards for forensic science, particularly standards initially developed by the U.S. Organization of Scientific Area Committees for Forensic Science (OSAC), this perspective paper raises concern about the publication of vacuous standards. Vacuous standards generally state few requirements; the requirements they do state are often vague; compliance with their stated requirements can be achieved with little effort - the bar is set very low; and compliance with their stated requirements would not be sufficient to lead to scientifically valid results. This perspective paper proposes a number of requirements that we believe would be essential in order for a standard on validation of forensic-science methods to be fit for purpose.

Experimental investigation of the mechanical properties of brain simulants used for cranial gunshot simulation.

The mechanical properties of the human brain at high strain rate were investigated to analyse the mechanisms that cause backspatter when a cranial gunshot wound occurs. Different concentrations of gelatine and a new material (M1) developed in this work were tested and compared to bovine brain samples. Kinetic energy absorption and expansion rate of the samples caused by the impact of a bullet from .22 air rifle (AR) (average velocity (uav) of 290m/s) and .22 long rifle (LR) (average velocity (uav) of 330m/s) were analysed using a high speed camera (24,000fps). The AR projectile had, in the region of interest, an average kinetic energy (Ek) of 42±1.3J. On average, the bovine brain absorbed 50±5% of Ek, and the simulants 46-58±5%. The Ek of the .22 LR was 141±3.7J. The bovine brain absorbed 27% of the .22LR Ek and the simulants 15-29%. The expansion of the sample, after penetration, was measured. The bovine brain experienced significant plastic deformation whereas the gelatine solution exhibited a principally elastic response. The permanent damage patterns in the M1 material were much closer to those in brain tissue, than were the damage patterns in the gelatine. The results provide a first step to developing a realistic experimental simulant for the human brain which can produce the same blood backspatter patterns as a human brain during a cranial gunshot. These results can also be used to improve the 3D models of human heads used in car crash and blast trauma injury research.