Theresa Stotesbury

Blood drop size in passive dripping from weapons

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.

Passive Drip Stain Formation Dynamics of Blood onto Hard Surfaces and Comparison with Simple Fluids for Blood Substitute Development and Assessment

The spreading dynamics of blood dripping onto hard surfaces is compared to two spreading models. Samples of human blood, porcine blood, and Millipore® water were dripped onto cardboard, foamcore, and glass surfaces in low velocity passive drip simulations. Final stain diameter, the total number of spines and scallops, and angle of impact were measured and analyzed. Spreading is best predicted by applying the concept of effective viscosity to the Scheller and Bousfield (R2 = 0.91) and Roisman (R2 = 0.89) spreading models. In the tested conditions, blood spreads with Newtonian tendencies; however, has quantifiable differences in stain appearance to Newtonian fluids like water. This is encouraging for the development of water‐based fluids as synthetic blood substitutes (SBSs). The work presents an assessment platform to quantify and score the performance of simple water‐based fluids using final stain diameter (6 points) and number of spines and scallops (6 points) at six dripping heights between 20 and 120 cm. The angle of impact of a stain alone is not a sensitive measure of SBS performance, but stain formation scores the SBSs performance with another 1 point. Together these features generate a quantitative relative ranking system, of a maximum possible 13 points, that can be used to support the use of a particular fluid for the creation of a drip stain. The performance of twenty simple fluids in the simulated dripping assessment test is described.

The application of silicon sol–gel technology to forensic blood substitute development: Mimicking aspects of whole human blood rheology

Solution-gelation chemistry has promising applications in forensic synthetic blood substitute development. This research offers a silicon-based sol-gel approach to creating stable materials that share similar rheological properties to that of whole human blood samples. Room temperature, high water content, silicon sol-gels were created using the organosilane precursors 3-glycidoxypropyltrimethoxysilane and tetraethylorthosilicate along with various concentrations of filler and pigment. Shear-thinning non-Newtonian properties were observed within most formulations of the presented materials. The effects of colloidal concentration, temperature, age and filler addition on the viscosity of the sol-gels were investigated. SEM-EDS analysis was used to identify the behavior of the fillers within the film and support their inclusion for basic bloodstain pattern simulation. A final proposed candidate sol-gel was assessed using a previously reported passive drip simulation test on a hard, dry surface and passed. This works represents encouraging development in providing safe material alternatives to using whole human blood for forensic training and research.

Design Considerations for the Implementation of Artificial Fluids as Blood Substitutes for Educational and Training Use in the Forensic Sciences

ABSTRACT Strengthening education and training in the forensic sciences requires the implementation of new and innovative technologies into existing teaching strategies. Scientific research in the design and use of artificial substitutes can offer new and advantageous contributions to such initiatives. This article describes the relevant considerations and advantages to designing a forensic blood substitute for use in forensic education and training facilities. BPA training materials must ensure safety, reliability, feasibility, and value added. Each of these considerations is addressed with a particular focus on the educational benefits (value added) that a forensic blood substitute can offer. In particular, the visual affordances of the material designed for this study will be highlighted in terms of its educational benefits to the training of scientists.

An Impact Velocity Device Design for Blood Spatter Pattern Generation with Considerations for High-Speed Video Analysis.

A mechanical device that uses gravitational and spring compression forces to create spatter patterns of known impact velocities is presented and discussed. The custom‐made device uses either two or four springs (k1 = 267.8 N/m, k2 = 535.5 N/m) in parallel to create seventeen reproducible impact velocities between 2.1 and 4.0 m/s. The impactor is held at several known spring extensions using an electromagnet. Trigger inputs to the high‐speed video camera allow the user to control the magnets release while capturing video footage simultaneously. A polycarbonate base is used to allow for simultaneous monitoring of the side and bottom views of the impact event. Twenty‐four patterns were created across the impact velocity range and analyzed using HemoSpat. Area of origin estimations fell within an acceptable range (ΔXav = −5.5 ± 1.9 cm, ΔYav = −2.6 ± 2.8 cm, ΔZav = +5.5 ± 3.8 cm), supporting distribution analysis for the use in research or bloodstain pattern training. This work provides a framework for those interested in developing a robust impact device.

Novel silica sol–gel passive sampler for mercury monitoring in aqueous systems

A novel passive sampler for mercury monitoring was prepared using organosilica sol-gel materials. It comprises a binding layer with thiol groups for mercury complexation and a porous diffusive layer through which mercury can diffuse and arrive at the binding layer. Our study demonstrated that this new sampler follows the principle of passive sampling. The mass of mercury accumulated in the binding layer depends linearly on the mercury concentration in solution, the sampling rate and the exposure time. A typical sol-gel sampler is characterized by a diffusive layer of 1.2 μm, in which mercury ions diffuse with a coefficient of D=0.09×10(-6) cm(2) s(-1), resulting in an uptake R(s) of 8.8 mL h(-1). The capacity for mercury uptake is approximately 0.64 μg cm(-2). Mercury diffusion and binding in the passive sampler are independent of the type of mercury-chloride complex, which potentially opens the door to use this device for mercury monitoring in a wide range of natural waters.

Investigation of Physical Effects of Acid Yellow 7® Enhancement on Dark and Non-Porous Surfaces in Impact Pattern Area of Origin Estimation

Abstract Impact patterns that are generated on dark surfaces can become camouflaged creating difficulties with conventional photographic methods that are used when estimating the area of origin. Chemical enhancement is an alternative technique that can be used to visualize these latent bloodstains. The application of Acid Yellow 7 to already fixed bloodstains provides a robust enhancement protocol which yields minimal stain distortion. Image J software was utilized to count stains, resulting in an approximate 5% increase in small stain detection post-enhancement. Area analyses also performed with Image J demonstrates that the average area of a single stain increases by a factor of approximately 1.24 post-enhancement. When using the BackTrack™ suite of programs this enlargement does not significantly affect the calculated impact angle of an enhanced bloodstain when compared to that of its original deposition (P= 0.585). As a result, the area of origin can be estimated within the accepted error of ± 7 cm from the known blood source.

The application of silicon sol–gel technology to forensic blood substitute development: Investigation of the spreading dynamics onto a paper surface

This work investigates the spreading dynamics of three candidate sol-gel solutions, of ranging viscosities, surface tensions and densities, and compares them with water and two commercial blood substitute products. Droplets were created with different sizes (10 to75μL) and impact velocities (1.4 to 6.0m/s) to strike 176gsm cardstock. Over 2200 droplets were created using the six different fluids and their final dried stain diameter was measured. Droplet spread was plotted using the Scheller and Bousfield correlation and uses effective viscosity as a parameter for non-Newtonian fluids. Comparing the results to an expected whole human blood range validated the spread of the candidate FBS sol-gel material in passive drip bloodstain pattern simulation. These findings complement the practical application of the material as a safe substitute for demonstrating droplet spread under controlled conditions on hard paper surfaces.

Three physical factors that affect the crown growth of the impact mechanism and its implications for bloodstain pattern analysis

This research uses high-speed video analysis of bloodstain impact events to investigate the influence of impact velocity, fluid depth and free-space on the characteristics of the mechanism. We focus on the changes in the crown growth over time. This work demonstrates qualitative differences in the impact mechanism under a range of impact conditions. These differences are further explained quantitatively as a function of measured crown width and height lengths over time. Fluid dynamic explanations of this growth are featured in the results and discussion. A comparison to water dynamics is reported. Our image analysis demonstrates that droplets are consistently formed at points which are different from the impactor/fluid interface and that this difference is fluid dependent. This fluid dependency demonstrates the importance of accurately modeling fluid dynamics of blood when designing and deploying blood substitutes in forensics applications.

The use of a forensic blood substitute for impact pattern area of origin estimation via three trajectory analysis programs

ABSTRACT This study explores the use of forensic synthetic blood substitute (FBS) for impact pattern simulation and area of origin estimation. Ten impact patterns were created at a known origin using the FBS and were analyzed by groups of undergraduate students participating in a basic bloodstain pattern analysis course. The students selected 20 upward-moving stains from their given patterns to estimate an area of origin. Three linear trajectory models – BackTrack™, Hemospat, and Sherlock – were used to estimate each patterns area of origin. Coordinate data from each models analysis were compared with the known origin and between programs at the x-, y-, z-coordinates, and overall. Results from this analysis yielded estimates comparable to the known. A one-way ANOVA found no significant difference between programs at the x- (p = 0.79), y- (p = 0.84), z- (p = 0.96) coordinates, and overall (p = 0.81). These results support the practical use of the FBS as an alternative to whole blood for impact pattern simulations and area of origin estimation.