Glass fractures

A forensic examination of glass

1. FORENSIC EXAMINATION OF GLASS & GLASS FRACTURES SUBJECT NAME – INTRODUCTION TO FORENSIC SCIENCE (IFS) STUDENT NAME – MUDASSAR PINJARI

2. glass is reasonably hard, transparent or translucent material composed of fused inorganic materials, primarily of silicon dioxide (sand) Glass is super cooled liquid, amorphous in nature. It found in many shapes, size ,colour and types. The wide variety of chemical compositions can alter its characteristics . GLASS

3. TYPES OF GLASS ,THEIR COMPOSITION & USES

4. Laminated glass Laminated glass is found in automobile windshields. Basically, it is two separate panes of plate glass adhered together with a clear laminated layer. It was designed to reduce injuries to passengers in cases of accidents Types of glass

5. • Tempered glass/ safety glass Tempered glass is a single pane glass that is durable and difficult to fracture due to its significant surface tension. When enough force is applied to break this surface tension the entire pane of glass fractures into thousands of small pieces (dicing). It is made stronger than ordinary glass by introducing stress through rapid heating and cooling of glass surface.

6. Terminology - • Radial cracks are fractures extending outward from the point of impact. • Concentric cracks are fractures forming in an approximately circular pattern around the point of impact. They are usually in straight segments that terminate in an existing radial crack. • Cone or crater (Hertzian cone) is a funnel-shaped area of damage caused by a high-velocity impact. • Wallner lines (ridges) are rib-shaped marks with a wave-like pattern. Wallner lines are called rib marks or ridges or conchoidal marks to describe their shape and are almost always concave in the direction from which the crack was propagating . • 3R Rule- Radial cracks form a Right angle on the Reverse side of the force. • Hackle is a line on the crack surface running parallel to the local direction of crack spreading. GLASS FRACTURES

7. A) Low-velocity impact fractures Low-velocity projectiles produce cracks in the glass, which radiate outward from the point of impact (radial cracks). If a pane is firmly held on all sides, concentric cracks can form around the point of impact. By observing the Wallner lines (ridges) on the radial cracks, the direction of breaking force can often be determined. Observe only the Wallner lines on the radial cracks nearest the point of impact. TYPES OF FRACTURES

8. B) High-velocity impact fractures A high-speed projectile striking a piece of glass will produce a cone or crater. If the projectile passes through the glass, the opening on the exit side will be larger than the opening on the entry side. The size of the hole and the diameter of the crater cannot be used to reliably predict the size of the projectile. Projectiles that pass through the glass at an angle to the surface produce an elongated hole. Radial cracks may also develop from high-velocity impact.

9. C) Thermal fractures In non-tempered glass a typical heat crack is curved, has a smooth edge, and has no indication of the point of origin of the crack. If a pane of glass has been cracked by the action of heat, it shows characteristic long wavy fractures. When glass is exposed to fire, it begins to melt at about 1200 degree Fahrenheit. It becomes runny at about 1600 degree Fahrenheit. Glass that contains many cracks indicates a rapid heat build-up. Glass that is heavily stained indicates a slow, smoky fire.

10. Mechanism of glass fracture

11. • After a striking force, glass first bends in the direction of applied force due to elasticity. • When the elastic limit exceeds, glass begins to crack beginning with the formation of a radial crack or fracture on the surface opposite to the penetrating force. • As the stress on the glass continues, concentric fracture form on the front surface (surface where penetrating or striking force applied) of the glass. • Fracturing continues with alternating radial and concentric fractures until the process ends. • When the first radial fracture begins, stress occurs along the edges closest to the point of impact, and the stress lines form called conchoidal fractures. • Conchoidal marks are shaped like arches. On the one side of the radial edge (near the point of impact), the rib marks form right angles i.e. perpendicular with the edge and nearly parallel to the opposite edge. • Since these conchoidal marks form right angles opposite the side from where the force is applied, they are useful to determine the direction of the applied force (3R Rule).

12. Forensic glass analysis A comparison of two or more glass fragments in an attempt to determine if they originated from same/different source(s). Glass evidences provides class as well as individual characteristics “EXAMINATION AND COMPARISON OF GLASS EVIDENCE”

13. Physical properties (colour,thickness) Optical properties (index or density) refractive Elemental analysis SEM LA ICPMS LIBS XRF ICP End of analysis End of analysis End of analysis NO NO NO YES YES YES MATCH MATCH MATCH Write report METHODOLOGY 15

14. Forensic glass examination has a well-established analytical pathway. First, glass fragments are recovered, observed, and identified by microscopy, usually using a stereomicroscope prior to cleaning. To examine the physical shape and colour of glass fragments. To examine a surface on a fragment. To examine other trace evidences such as fingerprints , hair, blood , fibers , etc. MICROSCOPIC EXAMINATION

15. COLOUR Colour may be used for purely aesthetic or for technical reasons. Comparing colour can distinguish between two or more sources of glass. side-by-side comparisons should be made with fragments of approximately equal and sufficient size. The fragments should be visually compared on edge, over a white surface, using natural light. LIMITATION : the fragments usually are too small and their colour density is too low, so it is not possible to perform colorimetry . Colourant Glass colours Iron Green, brown, blue Manganese Purple Chromium Green, yellow, pink Copper Blue, green, red Cobalt Blue, green, pink Nickel Yellow, purple Uranium Yellow, brown, green Titanium Purple, brown Carbon and sulphur Amber, brown Antimony sulphide Red Selenium Pink, red

16. physical examinations could easily corroborate the presence of glass materials vs other transparent materials. These observations are made in the preliminary stages of the analysis. The physical examination of glass can provide important information such as: Type of impact that caused the fracture of glass, e.g. a fracture caused by a gunshot, body impact, or by a hard object such a tool or bat. Direction of the force, e.g. to establish if a window was broken from inside or from outside. Type of material, which may be very useful to corroborate or invalidate alibi i.e. whether the glass is a flat architectural window, a tempered glass, a headlamp, or a container. Source of origin of the glass fragment, e.g. physical fit. Glass appearance (fresh v/s scratched and dirty pieces may be important to determine whether or not the glass transfer was recent, which is particularly important in the transfer of glass to shoes). 18 PHYSICAL MEASUREMENTS 18

17. Physical Fit A physical fit or physical “match” requires the edges of one fragment to perfectly fit into an edge of another , much like a jig-saw puzzle . (Almirall,2001). The match of pieces of glass is three dimensional and the analyst should document the details by aims of photography . The match should also be observed under the microscope in order to determine microscopic match of marks (striations, impressions, etc.). Figure. Photography of a physical match between a known fragment of glass and a questioned fragment of glass. 19

18. In cases where glass is recovered as a fragment that present the full thickness (original surfaces), it may be useful to measure the thickness of the glass. The thickness measurements can provide information about the possible type of object from where it comes, i.e. a vehicle side window , tempered glass, beverage bottle. To measure thickness, a micrometer or caliper with a precision of +/- 0.02mm or better should be used. When two glasses show significant differences in thickness, as determined by the variation in the known-source glass, they can be eliminated as originating from the same source. 20 2.Thickness Figure. Micrometer.

19. Density(D) is defined as the ratio of mass(M) to volume(V). D = M/V (g/ml) Density in glass can be assessed either quantitatively by direct measurement or qualitatively by simultaneous comparison of two or more specimens. Density is a function of chemical composition and atomic arrangement, which are controlled by the composition of the batch and the cooling history of the glass, respectively Accurate density measurements require a sample that is two to three millimeters in diameter 21 DENSITY

20. PRINCIPLE: ‘ solid particles will either float, sink or remain suspended in a liquid depending on its density relative to the liquid.’ Standard/reference glass particle is immersed in a mixture of bromoform and bromobenzene composition of mixture is adjusted until the glass chip remains suspended At this point (match point), the glass chip and the mixture have same density Glass chips of approximately the same size and shape as that of the standard are added to the liquid Liquid is transferred to the density meter 22 Floatation Method

21. 23 2.Displacement method The mass of the pieces of glass(M) is determined using suitable weight balance. The glass is then added to a graduated cylinder containing a previously measured volume of water(V1). After addition, the volume in the graduated cylinder is recorded again(V2). Using the below formula , density of the glass fragment can be determined. Density(D)=M/(V2-V1)

22. Refractive index is defined by Snell’s law as the ratio of the wave velocity in a vacuum to the wave velocity in the transparent medium.( Stoiber and Morse 1981). RI=V VACUUM / V GLASS RI is dependant on: 1)the wavelength of light 2)the temperature of the medium Refractive index (RI) is unitless RI is a function of chemical composition and atomic arrangement 24 REFRACTIVE INDEX

23. Significance of glass and glass fracture evidences • To aid reconstruction of crime scene • To provide information about the events which took place, and assisting in proving or disproving a witness’s story. • Glass fracture patterns are associated with burglary, criminal mischief, shooting incidents, and fire scenes. • To evaluate the direction of impact force applied (from inside out or outside in). • To calculate approximate force of impact, angle of impact of force. • To determine the type of glass fracture, the sequence of firing, direction of firing, and the type of firearm for the projectile holes present.

24. 1. Craig Elliott Kalani , February. On a dark, cloudy night in February, at 9:30 pm, a 19-year-old named Craig Elliott Kalani went for a walk with his dog in his neighbourhood but he never returned because a hit and run driver killed him. Pieces of glass were found on Craig's jacket and around his body at the crime scene. These pieces of glass helped crime scene investigators figure out what happened.  Police searched for a vehicle that had the same damage as the hit and run car. Then they found a car with those damages that belonged to Susan Nutt. In order to connect Susan's car to the glass fragments found at the crime scene to the glass on her car, refractive index tests needed to be done. This job was done by researchers at Oregon State University's Radiation Center . The scientists there found that the windshield glass contained the same 22 chemicals as the ones in Susan's car. They also said that both samples of glass were a definite match.   The glass evidence helped convict Susan Nutt. She failed to perform duties of a driver for an injured person. She was sentenced to 5 years in jail.  26 CASES STUDIES