Understanding of the Patterns and Shapes Formed when Blood Droplets Impact Upon Various Surfaces - Lab Report Example

Blood Pattern Analysis Student Name: Institution: Date: Introduction Over the past decades, bloodstain pattern analysis of human blood has acquired a greater recognition as blood spatter patterns are commonly found at crime scenes. Bloodstain pattern interpretation is usually undertaken to recreate the likely actions that may have caused the blood to spatter (Bevel & Gardner, 2008). Blood stain pattern expert analysts examine details such as location, size, shape, appearance of stains and patterns, geometry and location of the bloodstains to come up with opinions of what happened at a crime scene. Thus, it is important that blood stains are well documented and preserved so that they remain in their original state for later examination. The factors essential to be recorded in a bloodstain pattern analysis in order to have a correct interpretation of a bloodstain pattern include: the overall shape of the pattern, the shape of blood spatter, absorbance properties of the substrate, surface characteristics of the substrate, and the texture of the substrate (The Forensic Library, 2017). Bloodstain pattern analysis uses principles of biology, physics and mathematics to help forensic investigators to interpret bloodstain patterns correctly and answer questions such as: Why did the blood originate? What caused the bleeding? From what directions was the person wounded? How was the perpetrator and victim positioned as the time of the event? What movements occurred after wounding? How many crime perpetrators were actually present at a crime scene? Is there agreement between bloodstain evidence and witness statement? Bloodstain pattern analysis also provides information on what could have not possibly happen, assisting the investigator to reconstruct crime events, refute or support witness statement, include or exclude suspected perpetrators of the crime from the investigation, and exonerate perpetrators of a crime. Interpretation of a bloodstain pattern is subject to the information available and the analyst’s ability to perform the blood examination process (Albalooshi & Eltabie, 2015). Principles of Bloodstain Pattern Interpretation To understand how interpretation of bloodstains is performed, one must be able to the basic properties of blood. Analysts use the behavior of blood [biology], capillary action, cohesion, and velocity [physics], distance, geometry and angle [mathematics] to interpret bloodstain patterns. Blood is composed of both liquid part and solids part. The liquid part is made of blood plasma and serum, while the solids part is made of white blood cells, red blood cells, proteins and platelets (James, Kish, & Sutton, 2005). When inside the body, the blood is in liquid state. Except for people with hemophilic condition, blood does not remain in liquid state for long after exiting the body, but begins to clot in some few minutes to form a dark, shiny gel-like substance that hardens with time. Blood may exit from the body in different ways depending on how the injury is inflicted. These ways include: dripping, flowing, spurting, spraying, gushing or oozing [for wounds]. Because drops of blood demonstrate cohesion forces, or surface tension, they drop at an angle which may also be affected by the surface of impact (Bevel & Gardner, 2008). Smoother surfaces have little distortion whereas rougher surfaces affects the surface tension causing the drops to break apart. The location, number and volume of bloodstains influence the amount of useful information that can be gathered from a scene (Parker, 2014). In this practical, we performed a blood pattern analysis on artificial blood to study the patterns formed due to height impact, the angles of impact on different surfaces, blood smears, and also observed latent bloodstains. Aim of the Experiment The primary objective of this lab experiment was to gain an understanding of the patterns and shapes formed when blood droplets impact upon various surfaces and from different angles. This was achieved by: Learning the basics of bloodstain geometry Learning how to recognize blood patterns Learning how to document and interpret bloodstains Using chemiluminescence to detect bloodstains and learn how to avoid false positive results. Methods Materials: The following list of materials were required in order to complete the experiment: Artificial blood Disposable plastic pipettes Sheets of white A4 paper 30 cm square sheets of cardboard Acrylic and plywood Tissues/paper towels Tape measure Ruler Protractor Bluestar forensic training reagent with instructions Spray bottles Source of UV light Safety glasses Camera Procedures Part 1: Height impact Using a disposable pipette, some artificial blood was drawn up the pipette, ensuring no air bubbles are trapped and wiping the excess using a tissue. A single blood drop of the pipetted blood was dropped straight down at 90o on each of the surfaces provided from a height of 5 cm, 10 cm, 20 cm, 30 cm, 40 cm, 80 cm, 180 cm, and 210 cm, to observe and record the photographs of the patterns formed when the drops are wet, and after the drops were completely dry. Part 2: Angles of impact on various surfaces Blood was drawn into the pipette as in part 1 above. Each of the test surfaces was then placed at different angles to the floor, starting at 45o, then 60o and finally 70o. After setting the surfaces at these angles, a drop of blood was released at 30 cm above the surfaces, from an angle of 90o. The height was then adjusted to 60 cm and the test repeated. The patterns of the blood drops were then observed and photographed when the drops were wet and after drying completely. Part 3: Blood smears In this part, one blood smear and one contact pattern were made on separate pieces of plain white paper. The observations made were recorded with a scale bar in place. Results and Discussion Part 1: Height impact The photographs of blood stain pattern of blood dropped at 90o at heights of 5 cm, 10 cm, 20 cm, 30 cm, 40 cm, 80 cm, 180 cm, and 210 cm. Figure 1 [A-H]: Photographs of blood stain pattern dropped onto a surface from different heights at 90o. Calculating the Impact angle: The angle of impact refers to the angle that is formed when the blood drop hits the horizontal surface. The angle of impact is computed from the equation: Angle of impact = sin-1(W/L) Where: – Width of drop – Length the drop The calculations of impact angle are summarized in the table below: Table 1: Impact angle calculations Blood Drop Height of fall (cm) Width (mm) Length(mm) Angle of impact = sin-1(W/L) A 5 11.9 12.0 87.55o B 10 14.0 14.1 83.17o C 20 15.8 16.0 80.93o D 30 17.8 18.0 81.45o E 40 19.9 20.2 80.11o F 80 24.1 24.8 76.35o G 180 25.9 26.8 75.10o H 210 26.2 27.3 73.68o When blood drops from a height, it drops on a surface with a forceful impact. This causes the blood to split up into smaller droplets. The higher the height of dropping, the greater the force of impact between the surface and wet blood. From the photographs shown in figure 1 above, it is observed that as the drop height increases from 5 cm to 210 cm, more blood breaks into smaller droplets, and both the length and width of the drop increases as the drop height increases. At a greater height, with a greater force, blood drops typically produce smaller droplets, and the density of the blood drops decreases and moves further away from the initial blood impact source. This is observed from image C through to H (20 cm – 210 cm), but it is more pronounced in images G and H with drop heights of 180 cm and 210 cm respectively, where the blood drops move even further away from the initial source. It is also observed that as the blood drops strike the surface at an angle of 90o, it forms a stain with a circular shape. However, as the force of impact increases with increasing drop height, the size of the circular stain increases (Wonder, 2011). This can be observed by comparing the size of the drop in photograph A and that of the drop in photograph D through to H. A smooth textured surface, such as a polished tile, or a piece of glass, the surface tension would hold the drop in a circular pattern. Thus, in addition to the height of drop, the texture of the surface also has an effect on the outflow and the circular pattern (James, 1998). Essentially, surface tension allows the blood drop to collapse more uniformly. A smoother surface typically means a uniform rim outflow. Rougher surfaces such as wood and concrete distort the shape of a blood drop, making it less circular. The angle of impact reduces from 87.55o to 73.68o as the drop height increases from 5 cm to 210 cm. The increase in the length and width of the drops [drop size] is attributed to the velocity with which the blood drop sputters on the surface. This velocity increases with height because the force due to gravity increases with height. As the blood drops through air, they are deformed into different shapes and patterns and hit the surface at an angle slightly less than 90o. The higher the height of drop, the greater the effect of air pressure and subsequently, the greater the variation from the angle of origin (Kettner, et al., 2015). This explains why the angle of impact reduces from 90o to 73.68o. Determining the angle of impact, size and shape of blood droplets can assist forensic investigators to determine the convergent point [point of origin], how the victim lost the blood, the type of weapon used to perpetrate the crime and the amount of blood lost. Studying the blood drop impact spatter is also useful in providing an insight into how the victim and the perpetrator were relatively positioned with respect to objects during an event and the nature of the event (Gardner & Bevel, 2009). Part 2: Angles of impact on various surfaces In this part, the blood drops were released from heights of 30 cm and 60 cm, normal to the ground [90o], but with the target surfaces raised at varying angles. Figure 2 below shows the photographs of the drops taken during the experiment. Figure 2: Photographs of blood stain pattern dropped on different surfaces [wooden and ceramic tile] raised at angles of 45o, 60o and 70o. Impact angle calculations: The calculations of impact angle for the blood drops I to O are presented in table 2 below: Table 2: Impact angle calculations Blood Drop Height of fall (cm) Angle between target surface and the floor Width (mm) Length(mm) Angle of impact = sin-1(W/L) I 30 45o 14.9 17.2 60.0o J 60 45o 19.6 21.2 67.60o K 30 60o 22.1 40.0 33.54o L 30 70o 21.8 42.0 31.27o M 30 45o 22.3 27.0 55.68o N 30 60o 22.0 39.4 33.94o O 30 70o 22.4 37.1 37.14o From the images presented in figure 2, it is observed that the angle and the nature of surface has an influence on the shape and pattern of the blood drops. The droplets tend to be oblong shaped after hitting the surface. Blood pattern images I, J and M have angles of impact less than 40o (see table 2), which explains why the pattern of the drops has a tail shape with high ratio of length to width. The size of the drop is also influenced by the height of fall due to effects of air pressure as it travels through the air. The surface texture on which the blood drops plays a significant role on the shape of the blood pattern. As the blood drops hit a ceramic surface at an angle, they form a tail [see images K to O] which typically points the direction in which the blood drop was travelling before hitting the surface. On the other hand, wood has a rough surface and this explains why the blood patterns in images I and J have irregular, jagged edges that become more pronounced as the angle of impact between the source and the surface reduces, and as the impact height increases (Eckert & James, 1998). Cloth fabrics or carpets have soft surfaces which absorb blood, making it to spread more. These surfaces are absorbent and may alter the ratio of width to length of a blood stain, producing an incorrect angle of impact (White, 2004). This may in turn produce inaccurate reconstruction for locating the source of a blood pattern. From figure 2J, it is observed that as the blood strikes the rough wood surface, the blood drop breaks up into smaller particles. Part 3: Blood smears Figure 3 below shows a blood smear pattern on the upper part of the image, and contact pattern on the lower left part of the image. Figure 3: Blood smear and contact pattern It is observed that, smears form a larger pattern than contact pattern. Bevel & Gardner (2008) affirm that contact pattern is made when an object wet with blood comes into contact with a surface and transfers the blood stains onto the surface, while a smear is formed when blood are transferred to another surface by another object. A smear is also characterized by diminishing volume, as opposed to contact pattern that shows a larger volume of blood. The contact stains form a transfer pattern which is characterized by limited movement. Conclusion From the results obtained in this practical, we can conclude that the appearance of blood stain patterns is influenced by the force of the impact, angle and height from which the blood originate in relation to the surface, the characteristics of the surface on which the blood drop lands, the volume of the blood drop, as well as the manner in which the blood exits the source. Smaller heights of blood drop at an angle of 90o form rounded patterns than when the height is increased or the angle of the impact is varied. On the nature of surface, smoother surfaces produce rounded patterns compared to rougher surfaces that produce irregular, jagged edge patterns. Hence, by carrying out this practical, more understanding of the patterns and shapes formed when blood droplets impact upon various surfaces and from different angles has been achieved. References Answers to Review Questions Part 1: 1. [a] Texture of the surfaces: Ceramic surface – This surface can be described as hard, smooth and non-porous. Wood – Wood is rough, and porous [b] Edge characteristics of the stains: The blood stains formed on the ceramic surface are characterized by round, smooth edges, while the patterns formed on the wood surface are irregular and jagged in shape. [c] The diameter of the drops: (See in the practical, measured as length (mm) for the calculation of angle of impact). [d] Peripheral satellite spattering refers to small drops of blood breaking from the original spatter as the drop strike the surface. The extent of puttering is becomes more pronounced as the height of drop increases as in figure 1 H. It is also experienced more on rougher wood surface and less on smooth ceramic surfaces (see figure 2J). [e] Effects of changing the dropping height: The height from which a blood drops affects the size of the stain pattern. As the height of fall increases, the size of the blood stain becomes larger. The falling height also affects peripheral scattering and how far the small blood drop will travel from the initial drop. The extend of peripheral scattering increases as the height of fall increases due to increase in gravitational force acting on the drops. Part 2: 2. The size of the blood drop and even the shape falling from 30 cm is different from that of the drop released from a height of 60 cm, from an impact angle of 60o. The blood stain dropped at a height of 60 cm forms a larger pattern, and forms a longer tail than that released from a height of 30 cm. The variation on height causes variation in the velocity impact. 3. Smear and contact transfer patterns usually originate from either a primary or secondary transfer where an object with wet blood comes into contact with another object in the form of swipes, wipes, and smears. This basically means that the two patterns are the same (Hodge, Short, & Page, 2017). GENERAL 4. Blood stain pattern analysts can determine the direction of travel of blood drops by studying the shape that the blood sputter forms when it hits a target surface. The tail of the elongated blood drop usually points in the direction of travel. 5. It is possible to determine the angle of blood impact. To determine the angle of impact, we measure the width and the length of the blood stain. If the width is mm and the length is mm, then the angle of impact is determined as: Angle of impact = sin -1 () It should be noted that the tail of the stain is not measured when determining the angle of impact. This is because the tail is formed by the gravitational force and the impact force of the weapon used. The larger the size of the tail, the smaller the angle of impact. 6. Blood spatter analysis provides an interpretation of the events that may have occurred during a crime scene based on the knowledge that blood stains and blood patterns are characterized by the forces that created them. The accurate interpretation of blood stain patterns provides vital clues to investigators as to the nature of the crime, possible recreation of events, disturbances that may have occurred at a crime scene, the relative position of the victim and the perpetrator, or the evidence of weapons used (Albalooshi & Eltabie, 2015). The evidence collected is later used to either confirm or refute witness statement concerning events at the crime scene. 7. There are 3 main categories of stain groups that are based on the size of the stain and the magnitude of force with which the blood exits the source. The three categories help to understand the nature of the impact, as well as the force causing the blood stain pattern. Low velocity impact blood spatter - This spatter is caused by a force considered to be equivalent normal force due to gravitational pull (which is about 5 ft. /sec.). The stain formed with low velocity blood spatter is relatively large ( 4mm). Medium velocity impact blood spatter – The medium velocity blood spatter occurs when the origin of blood is subject to a force of 5-20 ft. /sec. The size of the resulting stains range within 1-4 mm in diameter. They are most associated with stabbings and beatings. High velocity impact blood spatter – This type of stains result from a source of blood that has been subjected to a force which is 100 ft. /sec. The stains obtained are predominantly 1 mm in diameter, although both large and small stains may be obtained. High velocity blood stains are typically associated with injuries resulting from gun shots.   Read More