C.S.I: Calculating Splatter Information
A Forensic Blood Analysis of Drop Height Diameters, Satellite
Numbers, and Finger Development.
Mayson Husband, 9th grade, Latta Junior High
Respectfully Submitted to the Oklahoma Junior Academy of Science
Abstract
The purpose of this experiment was to examine how drop height and type of
surface affect blood splatter diameter, number of finger extensions, and number of
micro droplet satellites formation. It was hypothesized that as height increases, blood
droplets will produce larger diameters, more fingers, and greater numbers of droplet
satellites. Also, it was hypothesized that the type of surface material will cause
significance variation in these characteristics.
Seven different surfaces (Resin, Ceramic tile, Asphalt tile, Wood, Glass, Sheet
Rock, and Concrete) were tested by dropping synthetic blood from six different heights
(15 cm, 30 cm, 45 cm, 90 cm, 105 cm, and 120 cm).
In general as the drop height increased the splatter diameter did also, but not in
every case (from 10.8 mm at a height of 15 cm up to 14.8 mm at a height of 120 cm).
The Resin surface produced the largest mean diameter at 15.7 mm and Wood
produced the lowest, 9.5 mm. As the drop height increased the number of fingers did
also, but not in every case either. The mean finger development for all surfaces
combined increased from 0 at a height of 15 cm up to 3.2 at a height of 120 cm with the
Sheet Rock surface at 5.8 fingers where Asphalt Tile produced the lowest, 0.8.
The mean number of satellites also increased with height (from 0.1 up to 6.3).
When all surfaces were compared, the Resin surface produced the highest mean with
4.1 satellites. The fewest number of satellites was produced by the Concrete surface
with a mean of 1.7.
Introduction
Bloodstain Pattern Analysis is one of several specialties in the field of forensic
science. Studying the drops of blood at the crime scene can help the investigators
determine what must have happened during the crime and the characteristics of the
person who committed the crime. The use of bloodstains as evidence isn’t new,
however the application of modern science has brought it to a higher level. New
technologies and advancement in DNA analysis are available for detectives and
criminologists to use in solving crimes and apprehending offenders.
Blood splatter evidence plays a key part in forensic science in forensic analysis.
Actually, it’s called Blood Pattern Interpretation. Herbert Leon MacDonell is the leading
authority on blood stain interpretation. It was his observations that lead the way. In his
published study, he gives the following tips to investigators: “It is possible to determine
the impact angle of blood on a flat surface by measuring the degree of circular distortion
of the stain. In other words, the shape of the stain tends to change depending upon the
angle of impact which caused the stain. For example, the more the angle decreases,
the more the stain is less circular and longer”. (2)
Surface texture is one of the key components in determining spatter type. By this,
MacDonell means that the harder the surface is, the fewer spatters will result. It is
therefore extremely important to duplicate the surface in a controlled test. When a
droplet of blood hits a surface which is hard as well as smooth, the blood usually breaks
apart upon impact. This in turn causes smaller droplets. The smaller droplets will
continue to move in the same direction as the original droplet. It involves reconstructing
the events that must have happened to produce the bleeding. It’s not something that
most law enforcement officials can do, it usually requires a specialist. The specialist will
try to determine what the position and shape of the drops indicate.
The science of physics is very closely linked to blood pattern interpretation.
He/She take measurements to determine the trajectory as well as execute carefully
controlled experiments. These experiments will use surface material like those found at
the crime scene to try to reproduce what has happened.
The smaller the size of blood splatter, the greater the energy required to produce
them. Low, medium, high velocity impact spatter may be identified by their respective
sizes but exceptions must also one be considered. Before a drop of blood can fall,
absent any other form of applied energy, gravitational attraction acting on blood must
exceed its surface tension. Diameter of a large bloodstain will be of little or no value in
estimating the distance a drop of blood has fallen prior to impact. When considering the
shape of a bloodstain for use in calculating its angle of impact, only a sharp, well
defined bloodstain should be used for measuring its width and length. Correct
interpretation of bloodstain patterns must include consideration of the surface texture of
the material upon which the bloodstains have been deposited. Surface tension prevents
spattering regardless of the distance a drop of blood has fallen before impacting a
smooth, hard surface, for instance glass. The water molecules in blood are both
cohesive and adhesive so they stick to themselves as well as other materials.
The purpose of this experiment was to examine how drop height and type of
surface would affect blood splatter diameter, number of finger extensions, and number
of micro droplet satellites formation. It was hypothesized that as height increases blood
droplets will produce larger diameter, more fingers, and greater numbers of droplet
satellites. Also, it was hypothesized that the type of surface material will cause
significance variation in these characteristics.
Procedure:
Simulated blood, from Carolina Biological Company, was loaded into pipettes
and suspended over seven different surfaces (resin, glass, concrete, sheet rock,
ceramic tile, asphalt tile, and varnished wood). The simulated blood had a density very
close to actual blood. The pipettes were perpendicular to the surfaces. The tips of three
replicate pipettes were fifteen cm from the surface, and then moved upward six times to
120 cm at fifteen cm increments. Single drops of simulated blood were squeezed out
onto the surfaces. A ruler was used to measure the diameter of each blood droplet. The
number of fingers (extensions from the main circular droplet) was counted. The number
of satellites ( micro droplets which landed away from the primary droplet) were also
counted and recorded. The mean diameters, number of fingers, and number of satellites
were calculated for each height and record the values in the data table.
Results
Three different types of analyses were made. One was for diameter, one was for
the number of fingers, and the other one was for the number of satellites that beyond
the main droplet. Seven different surfaces were evaluated for each of these
characteristics.
In general, as the drop height increased the splatter diameter did also, but not in
every case. The mean splatter diameter for all surfaces combined increased from 10.8
mm at a height of 15 cm up to 14.8 mm at a height of 120 cm. The Resin surface
produced the largest mean diameter at 15.7 mm where the Wood surface produced the
lowest at 9.5 mm. The results are seen in Graph 1 on the following page.
Graph 1:
In general, as the drop height increased the number of fingers did also, but not in
every case either. The mean finger development for all surfaces combined increased
from 0 at a height of 15 cm up to 3.2 at a height of 120 cm. The Sheet Rock surface
produced the largest mean finger development at 5.8 fingers where the Asphalt Tile
surface produced the lowest at 0.8 fingers. These results are seen in Graph 2.
Graph 2:
In general as the drop height increased the mean number of satellites did also
(from 0.1 up to 6.3). However, at the 120 cm height the mean dropped back to 4.5
satellites produced. When all surfaces were compared, the Resin surface produced the
highest mean number of satellites with 4.1 satellites produced. The fewest number of
satellites was produced by the Concrete surface with a mean of 1.7 satellites. The
results are seen in Graph 3. Data tables are found in the appendix section of this
paper.
Graph 3:
Analysis and Conclusion
The results of this experiment supported the hypotheses even though there was
not a perfect linear relationship between the drop height and the three tested factors of
satellite formation, diameter, and finger development. When the trend lines and slopes
were analyzed for each characteristic there was a stronger relationship between the
satellite formation and the drop height (m=1.83). The next strongest correlation was the
splatter diameter (m=1.41), and the least strong relationship was finger development
(m=0.38).
The mean diameters increased by 37% from 10.8 mm at 15 cm to 14.8 mm at
120 cm. The mean diameters produced by the Resin surface were 65% larger than the
mean diameters produced on the Wood surface.
Most likely the results were caused by the variations in the characteristic
properties of the seven different surfaces. When evaluating the surfaces, they varied in
porosity, hardness, and smoothness. Hard and smooth surfaces produced more
satellites. Porous materials produced greater numbers of fingers.
The results of this experiment can be important in crime scene investigations.
Blood splatters can provide information about the position and identity of the perpetrator
of the crime. It would be good to analyze blood splatters at different temperatures, on
more surfaces, and at different angles.
References
1.
Blackwell, B., Christner, K., Gamer, C., and Kelley, J. Physics of Bloodstains at a
Crime Scene retrieved from the internet at:
http://www.aspire.cs.uah.edu/aspire/bloodstains.html
2.
Forensic Fact Files, Bloodstain Pattern Analysis retrieved from the internet at:
http://www.nifs.com.au/FactFiles/dynamicblood/activites.asp?page=activities&title=
BloodStainPatternAnalysis.html
3.
Bloodstain Pattern Analysis. Retrieved from the internet at:
http://en.wikipedida.org/wiki/Bloodstain_pattern_analysis
4.
BCSO - Identification Division - Blood Spatter - General Information.htm
5.
BCSO Identification Division - Blood Spatter Terminology Page.htm
6.
Blood Spatter Analysis Lab.htm
7.
Benecke, M. and Barksdale, L. Distinction of Bloodstain Patterns from Fly Artifacts.
Forensic Science International, 137 (2003), 152-159.
Acknowledgements
Thanks go out to the following people: Mrs. Stevens for her hours spent at the
school helping me finish my project, my mom for her patience during science fair, and
Joe and Laura Reed for assisting me with my board.
Appendix: Data Tables
Surface
Height
Mean
Diameter
Mean Number of
Fingers
Mean Number of
Satellites
Resin
15 cm
12 mm
0
0.7
30 cm
14 mm
3.7
0
45 cm
15.7 mm
7.0
1.3
90 cm
15.7 mm
3.7
6.7
105 cm
16 mm
4.7
9.0
120 cm
20.7 mm
2.7
7.0
Surface
Height
Mean
Diameter
Mean Number of
Fingers
Mean Number of
Satellites
Asphalt Tile
15 cm
14 mm
0
0.3
30 cm
13 mm
0
0
45 cm
14 mm
0
1.0
90 cm
14 mm
2.6
5.3
105 cm
14.7 mm
0.6
5.0
120 cm
14 mm
1.7
7.7
Surface
Height
Mean
Diameter
Mean Number
of Fingers
Mean Number of
Satellites
Ceramic Tile
15 cm
12 mm
0
0
30 cm
12.7 mm
0.3
0.7
45 cm
15.3 mm
1.0
3.0
90 cm
13.3 mm
1.3
4.7
105 cm
14.6 mm
3.0
6.7
120 cm
15 mm
1.7
4.7
Surface
Height
Mean
Diameter
Mean Number
of Fingers
Mean Number of
Satellites
Wood
15 cm
6.3 mm
0
0
30 cm
10 mm
1.0
0
45 cm
9.7 mm
0
1.7
90 cm
12.3 mm
3.0
7.3
105 cm
13.3 mm
1.0
5.0
120 cm
15 mm
1.3
5.0
Surface
Height
Mean
Diameter
Mean Number of
Fingers
Mean Number of
Satellites
Sheet Rock
15 cm
5 mm
0
0
30 cm
8 mm
1.3
3.7
45 cm
10.7 mm
8.7
2.0
90 cm
13.3 mm
9.0
4.3
105 cm
12.3 mm
8.7
1.0
120 cm
13.3 mm
12.7
2.3
Surface
Height
Mean
Diameter
Mean Number of
Fingers
Mean Number of
Satellites
Glass
15 cm
10 mm
0
0
30 cm
10 mm
1.3
2.0
45 cm
13 mm
1.3
2.0
90 cm
13 mm
1.3
3.3
105 cm
13.3 mm
4.0
6.0
120 cm
13 mm
2.3
4.0
Surface
Height
Mean
Diameter
Mean Number of
Fingers
Mean Number of
Satellites
Concrete
15 cm
17.3 mm
0
0
30 cm
13.7 mm
0
1.7
45 cm
12.3 mm
1.3
1.7
90 cm
13.3 mm
1.7
2.0
105 cm
10.7 mm
3.0
3.7
120 cm
12.7 mm
0
1.0