Visualization of the air ejected from the temporary cavity in brain and tissue simulants during gunshot wounding

M. S. Lazarjan, P. H. Geoghegan, M. C. Taylor, Mark C. Jermy

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Abstract

One hypothesis for the physical mechanism responsible for backspatter during cranial gunshot wounding is that air is ejected by the collapse of the temporary cavity formed around the bullet path. Using bovine and ovine heads and simulant materials, evidence of this ejection was sought by measuring the velocity of the air that was drawn in and ejected from the cavity in front of the wound channel after bullet impact. A laminar flow of fog-laden air was arranged in front of the wound channel and two high speed cameras recording at 30,000 frames/second captured the air motion. All samples were shot with standard 9mm × 19 mm FMJ ammunition. Different concentrations of ballistic gelatine were used to characterize the effect of elasticity of the material on the velocity of the air. Fresh bovine and ovine heads were shot with the same experimental set up to investigate if there was induction of air into, and ejection of air from the entrance wounds. The results show, for the first time, that the temporary cavity does eject air in gelatine. The velocity of in-drawn air for 3, 5 and 10% concentration of gelatine was 81, 76 and 65 m/s respectively and the velocity of ejected air for 5 and 10% concentration of gelatine were 43 and 72 m/s respectively. The results show that when the concentration of gelatine is increased, the velocity of the air drawn into the cavity decreases and the velocity of the ejected air increases. However, no ejection was observed in 3% gelatine, ovine or bovine heads. Although ejection of air was not observed, ejection of brain from the wound channel was seen. Using the velocity of the ejected brain, the minimum intracranial pressure required to eject the brain tissue was estimated to be 712 kPa and 468 kPa for the sheep and bovine heads respectively.

Original languageEnglish
Pages (from-to)104-109
Number of pages6
JournalForensic Science International
Volume246
DOIs
Publication statusPublished - 1 Jan 2015

Keywords

  • Backspatter
  • Bloodstain pattern analysis
  • Brain tissue simulant
  • Cranial gunshot
  • Flow visualization
  • Temporary cavity

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    • 3 Article
    • 2 Conference contribution

    Experimental measurement of breath exit velocity and expirated bloodstain patterns produced under different exhalation mechanisms

    Geoghegan, P. H., Laffra, A. M., Hoogendorp, N. K., Taylor, M. C. & Jermy, M. C., 1 Sep 2017, In : International Journal of Legal Medicine. 131, 5, p. 1193-1201 9 p.

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  • Experimental and computational investigation of the trajectories of blood drops ejected from the nose

    Geoghegan, P. H., Spence, C. J. T., Wilhelm, J., Kabaliuk, N., Taylor, M. C. & Jermy, M. C., 1 Mar 2016, In : International Journal of Legal Medicine. 130, 2, p. 563-568 6 p.

    Research output: Contribution to journalArticle

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

    Lazarjan, M. S., Geoghegan, P. H., Jermy, M. C. & Taylor, M., Jun 2014, In : Forensic Science International. 239, p. 73-78 6 p.

    Research output: Contribution to journalArticle

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