NCJ Number
220412
Journal
Journal of Forensic Sciences Volume: 52 Issue: 5 Dated: September 2007 Pages: 1044-1049
Date Published
September 2007
Length
6 pages
Annotation
By examining the angled impacts of blood droplets onto paper, this study shows how equations can be used to determine the impact-velocity of blood droplets over a wide range of angles, for which the vertical impact is but one special case.
Abstract
Study results show that it is possible to use a single equation that takes into account the impact-angle when calculating a blood stain's size and number of spines. This information can then be used to determine the position of the source of the blood droplet. Previous results of studies at Cranfield University have shown that as long as the person counting the spines of a blood stain is consistent, useful equations can be found and used. The exact form of the equation for determining the number of spines will require further work with various liquids in order to determine the exact dependency of the number of spines. Currently, work has only been conducted with blood droplets on paper, so further work is required in order to determine whether there are any relationships for other surfaces and whether they can also be incorporated into a single equation for all surfaces by taking into account the contact angle and/or surface roughness. Before being used for crime-scene work, any equation developed must be validated with blind trials. Droplets of pig's blood were dropped onto paper at different angles to the horizontal in order to produce blood stains. Impact velocities varied from 1.82 to 5.76 m/sec, drop size from 3.7 to 5.0 mm in diameter, and the surface sloped at angles between 22.7 degrees and 90 degrees to the horizontal. From the data collected, a single equation was produced, relating stain size to drop size and velocity for all impact angles. 3 tables, 8 figures, and 21 references