Effect of muzzle gases on forward spatter of viscoelastic blood in close-range shooting

Abstract

Because bloodstain patterns resulting from close-range shooting are intrinsically different from those of long-range shooting, an accurate interpretation and delineation of these phenomena are essential in forensic science and crime scene analysis. Such a delineation would be helpful, for example, to distinguish whether a suicide or a homicide had happened. If the shooting was from a long-range (most likely a homicide), muzzle gases would not be able to influence blood spatter ejected from a victim. However, in the case of a close-range shooting, muzzle gases would greatly influence blood spatter. Herein, the effect of the muzzle gases on bloodstain patterns is studied. A de Laval nozzle is used to mimic an issue of supersonic “muzzle” gas from a gun barrel. The supersonic gas flow passes through a cylinder containing defibrinated sheep blood, which is blown off and atomized into numerous drops. These drops fly away and settle onto the floor or onto vertical walls at various distances from the cylinder exit. Viscoelasticity of the defibrinated sheep blood is enhanced by adding Xanthan to model different states of blood corresponding to different conditions. An impact of a vertically-released single drop onto an inclined substrate was also studied to elucidate splashing regimes/criteria of the blood drops of different viscoelasticity levels. We found that stronger elastic forces facilitated formation of bloodstains with higher ellipticity at a higher impact angles.

Impact of anti-coagulant choice on blood elongational behavior

“…21 Therefore, a quantitative understanding of the magnitude of the elongational viscosity is essential for studying physiological blood flow, including vascular flow instabilities, 22 as well as for the design and optimization of biomedical devices, such as cell sorters 23 and ventricular assist devices, 24 and for forensic investigations of blood stains. 9,25,26 Measuring the elongational viscosity of low-viscosity fluids is a challenging task. Besides some microfluidic technologies, 27 the most established method is the capillary break-up extensional rheometry (CaBER) that involves observing the thinning process of a capillary bridge between two plates that are drawn apart.…”