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    Blood drop size in passive dripping from weapons

    Year: 2013

    Journal: Forensic Science International, Volume 228, Issues 1–3, 10 May 2013, Pages 75–82, 20131119

    Authors: N. Kabaliuk 1, M.C. Jermy 1, K. Morisonb, T. Stotesbury 3 4,, M.C. Taylord, E. Williams 3 4

    Organizations: 1: Department of Mechanical Engineering, University of Canterbury, Private Bag 4800, Christchurch 8041, New Zealand, 2: Department of Chemical and Process Engineering, University of Canterbury, Private Bag 4800, Christchurch 8041, New Zealand, 3: Forensic Science, School of Chemical Sciences, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand, 4: Christchurch Science Centre, Institute of Environmental Science and Research, 27 Creyke Road, Christchurch 8041, New Zealand

    Passive dripping, the slow dripping of blood under gravity, is responsible for some bloodstains found at crime scenes, particularly drip trails left by a person moving through the scene. Previous work by other authors has established relationships, under ideal conditions, between the size of the stain, the number of spines and satellite stains, the roughness of the surface, the size of the blood droplet and the height from which it falls. To apply these relationships to infer the height of fall requires independent knowledge of the size of the droplet. This work aims to measure the size of droplets falling from objects representative of hand-held weapons. Pig blood was used, with density, surface tension and viscosity controlled to fall within the normal range for human blood. Distilled water was also tested as a reference. Drips were formed from stainless steel objects with different roughnesses including cylinders of diameter between 10 and 100 mm, and flat plates. Small radius objects including a knife and a wrench were also tested. High speed images of the falling drops were captured. The primary blood drop size ranged from 4.15 ± 0.11 mm up to 6.15 ± 0.15 mm (depending on the object), with the smaller values from sharper objects. The primary drop size correlated only weakly with surface roughness, over the roughness range studied. The number of accompanying droplets increased with the object size, but no significant correlation with surface texture was observed. Dripping of blood produced slightly smaller drops, with more accompanying droplets, than dripping water.