Journal of the American Society of Trace Evidence Examiners
Volume Number Four Issue Number Two AUGUST 2013
www.asteetrace.org
JOURNAL OF AMERICAN SOCIETY TRACE EVIDENCE EXAMINERS www.asteetrace.org Volume Number Four, Issue Number Two August 2013
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INSIDE THIS ISSUE
ISSN: 2156-9797
The Evidential Value of Fibers Used in Hi-Vis Workwear T. Coyle, M.Sc., C. Shaw, B.Sc., and L. Stevens, M.Sc.
Robyn Weimer, M.S.
ASTEE Journal Editor
c/o Virginia Department of Forensic Science 700 North Fifth Street
Richmond, VA 23219
[email protected]
2
Glycol Ethers: A New Category of Oxygenated Solvents Encountered in Fire Debris Samples Troy Ernst, M.S. and Kevin Streeter, B.S.
17
Plumbum Microraptus: Definitive Microscopic Indicators of a Bullet Hole in a Synthetic Fabric Christopher S. Palenik, Skip Palenik *Reprinted by permission of The Microscope
33
JASTEE Editorial Board:
Vincent Desiderio, New Jersey State Police Troy Ernst, Michigan State Police
JASTEE has established a working relationship with the
Amy Michaud, ATF National Laboratory
Jeremy Morris, Johnson Cty. Crime Laboratory
Scientific Working Group on Materials Analysis
Scott Ryland, FDLE Orlando Laboratory
(SWGMAT); whereby approved SWGMAT standards maybe
Bill Schneck, Washington State Police
published in JASTEE. These standards have been peer
Karl Suni, Michigan State Police
reviewed and approved by the SWGMAT group as a
Michael Trimpe, Hamilton Cty. Coroner’s Office
whole and thus were not subject to peer review through
Diana Wright, Federal Bureau of Investigation
JASTEE.
The mission of ASTEE is to encourage the exchange and dissemination of ideas and information within the field of trace evidence through improved contacts between persons and laboratories engaged in trace evidence analysis. The journal of the American Society of Trace Evidence Examiners is a peer reviewed journal
JASTEE has also established a working arrangement with The Microscope, the journal established and edited by
the McCrone Institute. Under this arrangement, articles published in JASTEE may be selected for publication in
The Microscope, and vice versa.
dedicated to the analysis of trace evidence. All original articles published in JASTEE have been subject to double-blind peer review.
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Coyle, et. al.: Hi-Vis Workwear Fibers
T. Coyle, 1 M.Sc., C. Shaw, 2 B.Sc., and L. Stevens,2 M.Sc.
The Evidential Value of Fibers Used in Hi-Vis Workwear ABSTRACT This paper investigates whether the finding of fluorescent fibers, typical of those seen in Hi-Vis workwear, have any evidential significance. This investigation was performed by combining a color block study (examining a number of samples of Hi-Vis workwear and assessing the extent to which they can be discriminated from each other), a population study (examining tapings taken from the general public to assess the extent to which Hi-Vis fibers are present on a person’s clothing at random) and a target fiber study (examining tapings taken from the general public to assess whether there are any fibers present that are microscopically and chemically indistinguishable from an individual sample of Hi-Vis clothing).
Two case studies are also presented involving the
examination of Hi-Vis fibers. The study shows that whilst it is possible to discriminate between garments constructed from Hi-Vis fabrics, there were instances where significant numbers of samples were found to be indistinguishable from each other. On that basis the authors recommend caution in the interpretation of findings involving HiVis workwear. Keywords: Hi-Vis, Fiber, Evidential Value, Polyester INTRODUCTION For many years, forensic fiber researchers in Europe have been conducting studies
known as ‘color blocks’ [1-8], where multiple sources of very specific colored fiber types
have been examined to determine the types of dyes used in their manufacturing and the degree to which a traditional forensic fiber comparison processes can discriminate
them. This approach, together with information from more traditional population and
target fiber studies, provides very valuable information to the forensic fiber expert. This
information can be used to aid case assessment, prioritize examinations and in the interpretation of fiber links in criminal cases.
Searching for textile fibers recovered from a surface of a textile is not always easy.
Whether or not that search is conducted on tapings, scrapings or vacuumed debris, the
search requires the examiner to be able to identify target fibers against a background of 1
Corresponding Author: Contact Traces Ltd, Unit 26, East Central 127, Milton Park,
Abingdon, Oxfordshire, UK 2
Contact Traces Ltd, Abingdon, Oxfordshire, UK Page 2 of 42
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Coyle, et. al.: Hi-Vis Workwear Fibers
other fibers, most of which are likely to be irrelevant to the criminal activity under
investigation. This task is further complicated by the fact that the most commonly worn colors of clothing are dark in shade, meaning that often forensic fiber examiners find
themselves searching for natural and synthetic fibers that are dark against a background of similar dark fibers.
Forensic fiber examiners are also required to identify populations of fibers, from which the source may be unknown. Such populations can provide valuable intelligence
regarding sources involved in contact with the garment or environments where the
garment may have been stored. The identification of such traces relies entirely on the
examiner to decide which fibers constitute a population and whether such fibers have any significance in the context of the case.
In our experience in casework, target fibers that stand out from the background fiber
population are likeliest to be identified as a fiber population worth pursuing. This
approach is open to criticism over the potential for selective bias, particularly if a fiber
population is selected purely on the basis that the population is distinctive. After all, the probative value of fiber types does not depend on how easy fibers are to find.
We are aware of at least one high profile case from the UK where fibers from high-
visibility (“Hi-vis”) workwear played a role in securing the conviction of a serial rapist [9]
and our casework experiences inform us that fluorescent fibers tend to stand out during examinations, but what value are they evidentially?
The demand for fluorescent, Hi-vis colored clothing has boomed worldwide over the last
few decades. The requirement for such Hi-vis textiles to be used as part of an
organization’s corporate responsibility has become part of health and safety
requirements worldwide, to the degree that the design and construction of such textiles is tightly regulated by governments across the globe (Europe EN471:2003, China
GB20653:2006, Canada CAN/CSA Z96.1-08, CSA Z96-09, USA ANSI/ISEA 207-2006,
ANSI/ISEA 107-2010, Australia/New Zealand AS/NZS 1906.4:2010, AS/NZS 4602:1999).
These standards are likely to be superseded by an International Standard ISO 20471 in the near future. Europe’s EN471:2003 regulation is typical of the restrictions imposed
on the clothing, and whilst it does not specify precisely the types of dyes required to be used in the clothing, it does specify the color space allowable in terms of chromaticity coordinates and luminosity of the material [10].
This work seeks to inform the forensic community regarding the evidential value of
fibers used in the construction of Hi-vis textiles. It comprises a color block study, a
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population study and target fiber study in relation to fibers that are used in the construction of Hi-vis clothing.
This study into these fiber types encompassed the following:
1. An assessment of the characteristics and discrimination of fibers used in the construction of 52 samples of Hi-vis clothing.
2. A population study of fibers, with the characteristics of Hi-vis fibers, on tapings taken from 100 garments.
3. A target fiber study of tapings taken from 100 garments for the presence of specific Hi-vis fibers from the samples examined in part 1.
4. Two case examples of Hi-vis fibers recovered during criminal fiber examinations.
Overall, this paper provides a discussion on the value of finding Hi-vis fibers as evidence in cases.
MATERIALS AND METHODS
Fabric samples Fifty-two Hi-vis fabric samples were obtained from 50 Hi-vis garments being worn by various workers in a busy business park over a period of a few weeks. Samples were taken by cutting a square of fabric out with a scalpel (to obtain a known sample) and by means of a taping of the surface (to assess the sheddability of the fabric). In the laboratory, the 52 samples of fabric were examined using a Leica MZ16 stereomicroscope (magnification range 7.1x – 115x). A representative sample of the fibers from each fabric was removed and mounted on microscope slides in Entellan® under glass cover-slips. Table 1 provides a list of these samples. Constituent fibers were identified using a Leica DM EP polarized light microscope (PLM) at magnifications between 100x and 400x. Information about the color, cross section, diameter and luster of the fibers was recorded and the birefringence characteristics were used to give an initial identification of the fiber type. The constituent fibers were classified according to their thickness, color and cross sectional shape. All of the samples of the Hi-vis clothing were compared to each other by comparison microscopy. A Leica FS 4000 comparison microscope with transmitted white light (bright field) and reflected incident light (equipped with Leica narrow banded excitation filters UV (A) and Blue (I3)) was used.
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Table 1. Collected fabric samples and sheddability information from Hi-vis garments No.
Manufacturer
Garment Type
Color
Label Description
# fibers on shed tape
1
Viz Lite
Yellow
100% Polyester
1
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 17a 18 19 20 21 22 23 24** 25 26 27* 28 29 30 31 32 33 34 35 35b 36 37 38 39 40 41 42 43 44 45 46 47 48
Yokotex JSP Unknown
Green
No label 100% Polyester No label
4 0 1 2 6 1 N/A 0 2 0 1 3 7 1 1 69 50 50 80 8 6 0 0 2 0 0 3 4 1 0 2 3 51 1 4 10 1 5 3 8 2 9 0 11 0 N/A 12 31 4
Uneek Unknown Strada Functional Aggressive Safety Unknown Wceng
100% Polyester Vest
100% Polyester BSEN 471 No label 100% Polyester
Jacket Unknown
Yellow Vest
ARCO Unknown Leo Workwear Beartex Dimensions
100% Polyester BSEN 471:2003 100% Polyester BSEN 471:94 Dir
Inside Mesh Vest T-Shirt Vest Coat
100% Polyester No label 100% Polyester BSEN 471:1994
Leo Workwear Retromax ST Workwear Buck and Hickman H Protection Work
100% Polyester Orange Yellow Green
Vest
Unknown
Yellow
Sainsbury's Unknown UPS Partwest Royal Mail
Orange
Unknown
100% Polyester BSEN 471:2003 No label 100% Polyester No label
100% Polyester Dir 89/686/EEC 100% Polyester
No label
Yellow T-Shirt Orange
Vest
100% Polyester BSEN 471:1994 100% Polyester BSEN 471:2003
Yellow
Inside Mesh
Virgin
Red
No label
Vest Yellow Unknown
TP Worksafe Unknown
Jacket Jumper Inside T-Shirt
Orange
Vest
Yellow
100% Polyester BSEN 471:2003 100% Polyester Dir 89/686/EEC
No label
100% Polyester BSEN 471:2003
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49 50 51 * ** N/A
Coyle, et. al.: Hi-Vis Workwear Fibers
Hoody Jacket TP Worksafe Vest Label states- ‘Does not conform with Hi-Vis BSEN:471’ No sample present No sheddability tape taken Dickies
100% Polyester BSEN 471:2003
Spectral characteristics of all of the identified fiber types in each of the 52 samples were analyzed using a Zeiss/TIDAS Microspectrophotometer (MSP) in the region of 380 nm – 730 nm. The spectral characteristics of the fibers were compared in order to determine the level of discrimination across the samples obtained. A selection of fibers was analyzed with a Thermo DXR Smart Raman Microscope using both a 532 nm and a 780 nm laser. Spectra were obtained over a range of 2000 – 200 cm-1. The chemical composition of some of the fibers was determined using a Thermo Nicolet iN10 Fourier Transform Infrared (FTIR) spectrometer. Fibers were flattened using a diamond window and placed into the path of the IR beam. Spectra were obtained over a range of 4000 – 650 cm-1.
Population study – clothing From a previous study [7], tapings had been taken from 100 every-day garments worn by several volunteers over a period of time. Tapings were taken by using low adhesive tape-lifts which were secured to clear plastic sheets. One tape-lift was used to tape the front of the garment and one to tape the back of the garment. It is accepted that some of the garments in this study may have been worn by people who shared similar environments such as workplace, home or transport. These tapings were examined for any fibers that could have come from a Hi-vis garment (selected by color) using a Leica MZ16 stereomicroscope. Target fibers were identified, removed and mounted on microscope slides in Entellan® under glass cover-slips. Microscopic identification was performed as previously described for the 52 fabric samples.
Target fiber study – clothing All fibers recovered from the tapings of the garments used in the population study that were identified as being visually similar to those typical of the type used in Hi-vis clothing were compared to the Hi-vis fabric samples. If fibers were found to be
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microscopically indistinguishable, under all of the lighting conditions, the MSP spectra of the fibers were compared.
Case Examples Two case examples involving Hi-vis clothing are described in the context of the findings of this research. RESULTS
Fabric samples Sheddability of the Hi-vis garments was assessed by placing a strip of sellotape on the garments once and recording the number of constituent fibers present, as shown in Table 1. Of the areas samples 22% yielded no constituent fibers on the sheddability tape and 26% had either one or two fibers present. Thirty percent of the areas sampled yielded between three and nine fibers, 22% yielded 10 fibers or more. Seven sources yielded over 30 fibers and can be considered to be shedding fibers considerably well. The majority of samples (83%) were yellow in color; the other colors found were red, orange or green. Without exception, the fabric samples consisted of fabric constructed using a single color. All of the 52 fabric samples were constructed from polyester fibers (Table 2). Fifty-two percent were constructed from a single type of polyester fiber, whereas the remaining 48% consisted of a blend of more than one type of polyester fiber. Most blends consisted of two fiber types; however two fabric samples were constructed from blends of more than two fiber types. In terms of levels of delustrant particles, 87% of the samples contained fibers that were classified as being “semi-dull”, whereas 27% contained fibers classified as “bright”. Some samples were constructed solely of “bright” fibers, whilst some formed a blend of “semidull” and “bright” fibers. Owing to the small number of red, green and orange samples only the yellow samples were analyzed in further detail for the purposes of this study. The fiber types contained within the remaining 43 samples were separated morphologically, according to their thickness, cross-section and levels of delustrant particles; thus giving 69 identified fiber
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types. They were compared against each other under the microscope. It became evident through this exercise that comparison of the fibers under incident light fluorescence was very difficult due to the intensity of the fluorescence, rendering it difficult to discriminate between fibers of the same color and morphology. The microscopic color of the fibers was very consistent from one sample to another and did not in itself contribute much, if anything, to the discrimination of the fiber samples. The most discriminating features of these samples using comparison microscopy were morphological ones, namely: thickness, delustrant levels and cross-section. Table 2. Microscopic properties of fabric samples SAMPLE
BLEND
FIBER TYPE
COLOR
1 2 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 10 11 11 12 12 13 14 14 15 16 16 17 17 17A 18 19 20 20 21 22
NO NO NO YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES NO YES YES NO YES YES YES YES NO NO NO YES YES NO NO
POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER
YELLOW GREEN YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW
LUSTRE SEMI SEMI SEMI SEMI BRIGHT SEMI BRIGHT SEMI BRIGHT SEMI BRIGHT SEMI SEMI SEMI SEMI SEMI SEMI BRIGHT SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI BRIGHT BRIGHT SEMI SEMI SEMI BRIGHT
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DIAM (μm)
CROSS-SECTION
17.5 20 15 15 10 17.5 12.5 17.5 12.5 12.5 10 20 15 17.5 15 15 15 10 15 17.5 12.5 17.5 20 25 15 15 12.5 15 12.5 17.5 17.5 10 10 17.5 15 20 10
TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL ROUND ROUND TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL TEXTURED / TRILOBAL TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL ROUND ROUND ROUND ROUND TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL ROUND
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SAMPLE
BLEND
FIBER TYPE
COLOR
23 25 26 27 28 29 29 30 31 32 33 34 34 35 35 35B 36 37 38 39 39 40 40 41 41 41 42 43 44 45 45 46 46 47 47 48 48 49 49 50 51 51
NO NO NO NO NO YES YES NO NO NO NO YES YES YES YES NO NO NO NO YES YES YES YES YES YES YES NO NO NO YES YES YES YES YES YES YES YES YES YES NO YES YES
POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER POLYESTER
YELLOW RED YELLOW GREEN YELLOW YELLOW YELLOW RED YELLOW YELLOW YELLOW ORANGE ORANGE YELLOW YELLOW YELLOW RED RED RED YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW ORANGE YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW YELLOW
LUSTRE BRIGHT SEMI BRIGHT SEMI SEMI SEMI BRIGHT BRIGHT SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI BRIGHT BRIGHT SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI SEMI
DIAM (μm)
CROSS-SECTION
10 17.5 10 25 20 15 10 10 17.5 15 12.5 15 17.5 20 17.5 20 20 20 20 17.5 17.5 17.5 17.5 15 17.5 10 12.5 15 22.5 17.5 20 20 17.5 20 15 17.5 17.5 15 22.5 20 17.5 17.5
ROUND TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL TEXTURED / TRILOBAL ROUND ROUND ROUND TEXTURED / TRILOBAL TEXTURED / TRILOBAL TEXTURED / TRILOBAL TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL TEXTURED / TRILOBAL TEXTURED / TRILOBAL TEXTURED / TRILOBAL TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL ROUND ROUND ROUND ROUND TEXTURED / TRILOBAL TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL ROUND TEXTURED / TRILOBAL TEXTURED / TRILOBAL TEXTURED / TRILOBAL TEXTURED / TRILOBAL ROUND
MSP analysis of the yellow samples showed that the sample set consisted of three different types of spectra. Thirty-four of the samples produced spectra consisting of a doublet (maximum at approx. 440 nm and a shoulder at 460 nm, Figure 1), these were indistinguishable from each other. Three of the samples produced spectra consisting of a single band with a symmetrical shape (single maximum at approx. 447 nm, Figure 2), these were indistinguishable from each other. Five of the samples produced spectra with
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a single band with an asymmetrical shape (single maximum at approx. 442 nm, Figure 3) these were indistinguishable from each other. Only one sample contained multiple fiber types whose MSP spectra differed within the sample (sample 46).
Figure 1 Spectra from several samples showing a ‘doublet’
Figure 2 Spectra from two samples showing a “symmetrical” curve
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Figure 3 Spectra from several samples showing an “assymetrical” curve
When the findings from comparison microscopy and MSP were combined, the samples could be sub-classified into eight separate groups which contained fibers that were indistinguishable from each other, and 11 individual samples that were distinguishable from all others (Table 3). Table 3. Distinguishable fiber groups after both comparison microscopy and MSP spectroscopy Semi-Dull (≤15μm)
Semi-Dull (>15μm)
Round No. of Group Samples
Textured No. of Group Samples
Round No. of Group Samples
Textured No. of Group Samples
A
(D)
4
B
(D)
6
E
(D)
13
F
(D)
14
Unique
3
C
(S)
2
Unique
1
G
(As)
2
D
(D)
5
Unique
1
Unique
5
Bright Group H
No. of Samples
NOTE:
(D)
Doublet in the MSP spectrum
(D)
12
(As)
Asymmetrical band in the MSP spectrum
Unique
1
(S)
Symmetrical band in the MSP spectrum
Raman analysis of the fiber samples did not yield much in the way of useful spectral data of the dye. Using 532 nm laser excitation most of the samples fluoresced so much that no spectral data was obtained, on only a few samples were some bands observed
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and these arose from the polyethylene terephthalate (PET) polymeric constituent of the fibers. At 780 nm there was significantly less fluorescence however only bands arising from PET were observed.
Population study - clothing Thirty-eight of the 100 every-day garments contained fibers on their surfaces considered to be likely to have arisen from “Hi-vis” sources. Sixty-five fibers were recovered from these garments (Table 4). Most were either yellow (42%) or orange (45%), with the remainder (14%) being green. One recovered yellow fiber was lost prior to identification and therefore was not included in subsequent calculations. Thirty-three percent of the fibers were polyester, 27% were wool, 19% were cotton and the remainder consisted mainly of acrylic and cellulosic fibers. The largest number of such fibers found on any garment was four. Eighty-two percent of the garments where “Hi-vis” fibers were found contained one or two fibers only.
Target fiber study - clothing All of the fibers recovered from the clothing were compared to the samples of Hi-Vis garments. None of the fibers recovered from the clothing were indistinguishable from any of the 52 samples of “Hi-vis” clothing.
Case examples Case 1 - Offenders stole a construction vehicle (JCB) and used it to extract a cash machine (ATM) from the wall of a bank. Tapings were submitted for examination. Two fibers were found on the tapings from the JCB that were considered likely to have come from yellow Hi-vis clothing. One of these fibers was found to be microscopically and chemically indistinguishable to fibers used in the construction of several Hi-vis garments sampled in this study. Case 2 - A cyclist was involved in a hit-and-run with a vehicle. The cyclist’s jacket was Hi-vis (a light waterproof material) and was found to be constructed from a yellow nylon exterior and a yellow polyester mesh interior. A vehicle was examined several weeks later and fibers were recovered from the hood and roof. Three Hi-vis yellow polyester fibers were found on the outside of the vehicle, however, all three fibers differed in cross-section from those used in the construction of the inside mesh of the cyclist’s
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jacket. No fibers were found that could have come from the yellow nylon material that comprised the outer shell of the cyclist’s jacket. Table 4. Hi-Vis fibers found on the surfaces of clothing Garment Number and Description
# of Fibers
Yellow
Microscopic Color Green
Orange
Polyester
Wool
Microscopic Identification Cellulosic
Acrylic
Cotton
Other
2 - Blue Top
2
2
-
-
1
-
-
-
1
-
6 - Blue T-Shirt & Trousers
2
2
-
-
2
-
-
-
-
-
11 - Blue & White T-Shirt & Denims 12 - Blue Jeans
1
-
-
1
-
-
1
-
-
-
2
-
2
-
-
-
-
-
2
-
13 - Blue Jeans
4
1
2
1
-
-
-
-
4
-
15 - Grey Hooded Top
1
1
-
-
-
-
1
-
-
-
16 - White, Red & Green T-Shirt 21 - White T-Shirt
1
-
-
1
-
-
-
1
-
-
2
1
-
1
-
1
1
-
-
-
22 - White Blue Striped TShirt 23 - Blue T-Shirt
3
2
-
1
2
-
-
1
-
-
2
2
-
-
1
-
-
-
1
-
25 - Grey & Black Top
3
2
1
-
2
-
-
-
-
1
26 - Black T-Shirt
1
1
-
-
1
-
-
-
-
-
28 - Brown T-Shirt
1
1
-
-
1
-
-
-
-
-
32 - Beige/Yellow T-Shirt
3
-
-
3
3
-
-
-
-
-
38 - Grey Rugby Shirt
1
1
-
-
-
-
1
-
-
-
40 - Black Trousers
4
1
-
3
-
4
-
-
-
-
42 - White Shirt
1
1
-
-
-
-
-
-
1
-
44 - Beige Top
2
1
-
1
1
-
-
-
1
-
45 - Blue T-Shirt
2
-
1
1
1
1
-
-
-
-
46 - Blue & Grey Jacket
1
-
-
1
-
-
-
-
1
-
48 - Black Fleece Jacket
2
-
-
2
1
-
-
1
-
-
53 - Green Top
3
-
-
3
-
2
-
-
-
1
55 - Black Top
2
-
-
2
2
-
-
-
-
-
59 - Yellow T-Shirt
1
1
-
-
-
1
-
-
-
-
62 - Pink T-Shirt
1
-
1
-
-
1
-
-
-
-
63 - Green top
1
-
-
1
-
-
-
1
-
-
64 - Grey Cardigan
1
1
-
-
1
-
-
-
-
-
66 - Blue Skirt
1
-
1
-
-
-
-
-
-
1
73 - Blue Dress
1
1
-
-
-
-
1
-
-
-
74 - White Shirt & Black Trousers 76 - Blue Jeans
1
-
-
1
-
1
-
-
-
-
1
1
-
-
-
-
1
-
-
-
77 - Black Blazer
1
-
-
1
-
1
-
-
-
-
78 - Teal Jumper
1
-
-
1
-
1
-
-
-
-
82 - Grey Top
2
1
-
1
-
1
-
1
-
-
87 - Blue Jeans
1*
1
-
-
-
-
-
-
-
1
90 - Navy Polo Shirt
1
1
-
-
-
1
-
-
-
-
94 - Blue Jumper
1
1
-
-
-
1
-
-
-
-
95 - Blue Jumper
4
-
1
3
2
1
-
-
1
-
Total
65
27
9
29
21
17
6
5
12
4
* Fiber lost prior to identification.
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Coyle, et. al.: Hi-Vis Workwear Fibers
DISCUSSION AND CONCLUSIONS The construction of Hi-vis clothing used for textiles is subject to very strict regulation and this, the authors believe, has led to a very high degree of uniformity between samples, far higher than would be expected from the general textile market. In relation to the most commonly occurring colored sample, yellow, the microscopic comparison was mainly found to be of value when samples were compared based on the morphological characteristics of the fibers, namely their thickness, cross-section and levels of delustrant particles. Comparison using incident light fluorescence was less effective than expected, in general the samples fluoresced very brightly within a narrow range of color. MSP analysis offered additional discrimination of samples, but not to the degree observed in other studies for other types of colored fibers. When considered together the combination of comparison microscopy and MSP (visible range) only managed to separate a small sample set of randomly chosen clothing into a small number of groups, some of which were densely populated by samples indistinguishable from each other. Raman and FTIR analysis did not assist in discriminating any further. We can conclude from this study that when compared to normal colored clothing and textiles, yellow Hi-vis garments are generally poorly discriminated from each other using traditional methods. Eight percent of the every-day garments chosen at random were found to contain yellow polyester fibers on their surfaces. Where such fibers were found, the highest number recorded was two. It is therefore reasonable to expect fiber examiners to encounter these fibers as part of their general case working experiences, although only a small number of fibers. We believe that the reason that so few fibers are encountered so infrequently on clothing is that 48% of Hi-vis sources did not tend to shed fibers well (i.e. two or fewer fibers noted on sheddability tapings), reducing the pool of fibers transferred during contact amongst the general population. No fibers were found on the everyday garments that could have come from the Hi-vis clothing samples in this study. This is somewhat surprising given how difficult it was to discriminate the samples from each other. However, given the low number of fibers recovered from the tapings and the fact that 48% of the sources in this study did not tend to shed, it should not be regarded as unusual.
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Coyle, et. al.: Hi-Vis Workwear Fibers
There was also a considerable number of Hi-vis type fibers recovered from these everyday garments that were not polyester. We are aware that Hi-vis colored fibers are used in a wide range of garments that are not workwear, including sports and leisure wear and winter clothing (fleeces, hats and gloves). It is possible that sources of leisure wear do not fall under the regulatory requirement as they are not supplied by an employer to an employee for the purposes of work activity. On that basis they may fulfill a requirement of being “Hi-vis” (i.e. fluorescent and/or reflective) without meeting the precise regulatory needs in terms of luminosity and color space. We believe that the case example of the cyclist’s jacket illustrates this point clearly showing that just because a garment is Hi-vis, does not necessarily mean that it should be treated as a poor target fiber type. This does however present somewhat of a conundrum for those who need to interpret the findings in a case where yellow Hi-vis fibers are found on a surface that are indistinguishable from clothing of an offender. Whilst it may be unlikely to find such fibers on clothing by chance, the discrimination power in respect of such samples is so low that it raises the possibility that the fibers arose from a source other than the questioned garment. It is our opinion that in general, interpretation of the evidential value of a textile fiber link involving these types of fibers should be treated with considerable caution. In particular, for case assessment purposes, pursuing such links should generally be given a low priority, unless there are case circumstances that dictate otherwise – such as supporting witness testimony that an offender wore such an item of clothing, or determining whether or not a weapon was used to damage the clothing, or the use of non-polyester Hi-vis fibers in the construction of the garment. In the case of the hitand-run cyclist, three Hi-vis fibers were found on the outside of a car seized shortly after the alleged offence occurred. However the car was in a secure storage area for several weeks prior to the fibers being recovered by police. It was our view that the three (non-matching) Hi-vis fibers more likely arose from environmental factors. This demonstrates that in cases involving Hi-vis fibers, there is a need to understand what other sources of Hi-vis fibers could have been involved, particularly given how prolific the use of Hi-vis clothing is amongst police, paramedics, fire-fighters and other emergency services.
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The manufacturing of Hi-vis clothing is an excellent example of government regulating the textile industry in terms of its manufacturing, to produce a product of very high uniformity in order to accomplish a very specific task of protecting employees’ health and safety. It is in complete contrast to the manufacturing of clothing for everyday wear, which by its very nature requires manufacturers to produce clothing that is highly variable by design and construction. REFERENCES 1. Grieve MC, Biermann TW, Schaub K. The individuality of fibers used to provide
forensic evidence - not all blue polyesters are the same. Sci Justice 2005; 45(1):13 –
28.
2. Grieve MC, Biermann TW, Schaub K. The use of indigo derivatives to dye denim material. Sci Justice 2006; 46(1):24-26.
3. Grieve MC, Biermann TW. The evidential value of black cotton fibers. Sci Justice 2001; 41(4):245-260.
4. Biermann TW. Blocks of colour IV: The evidential value of blue and red cotton fibers. Sci Justice 2007; 47(2):68–87.
5. Grieve MC, Biermann T. The occurrence and individuality of orange and green cotton fibers. Sci Justice 2003; 43(1):5–22.
6. Grieve MC, Deck S. Black cellulosic fibers - a "bete noire"? Sci Justice 2002; 42(2):81– 88.
7. Jones J, Coyle T. Synthetic flock fibers: A population and target fiber study Sci Justice 2011; 51(2):68–71.
8. Jones J, Coyle T. Automotive flock and its significance in forensic fiber examinations Sci Justice 2010; 50(2):77–85.
9. Wiggins K, Cheshire S. The M25 Rapist, Proceedings from the European Fiber Group Meeting, Prague 2004:134-140.
10. Szuster L, Kaźmierska M, Król I. Dyes Destined for Dyeing High-Visibility Polyester Textile Products Fibres Text East Eur January/March 2004; 12(1):70-75.
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Troy Ernst,1 M.S.
Ernst & Streeter: Glycol Ethers
and Kevin Streeter, 1B.S.
Glycol Ethers: A New Category of Oxygenated Solvents Encountered in Fire Debris Samples ABSTRACT In early 2010, information was received regarding the possible involvement of scented oils containing glycol ethers in intentionally set and accidental fires. Based on comparisons of mass spectral library search results and information from Material Safety Data Sheets from scented oils, it was discovered that a case that had been recently analyzed in the authors’ forensic laboratory may have contained these compounds. Consumer products containing glycol ethers – mostly plug-in room fresheners and vehicle deodorizers – were purchased for analysis. Additionally, reference standards of several glycol ethers were obtained from The Dow Chemical Company (“Dow”) 2. The consumer products and the glycol ether reference standards were subjected to flame tests and analyzed by gas chromatography – mass spectrometry (GC-MS). Some of the glycol ether reference standards showed agreement in retention times and mass spectra to the consumer products and to the case samples. In the last three years, several case samples containing oxygenated solvents consistent with glycol ether reference standards have been encountered. Identification of these compounds may provide arson investigators with probative information in regards to crime scene observations and/or fire causation. Keywords: Fire debris, Oxygenated solvents, Glycol ethers, DOWANOL™, Scented oils, Air fresheners, GC/MS INTRODUCTION The ignitable liquid classification scheme within ASTM International 3 E1618-11 [1]
encompasses most ignitable liquids that are encountered in the forensic analysis of fire debris. Laboratories often develop reference collections of ignitable liquid consumer products for comparison to fire debris samples. Occasionally, a fire debris analyst
comes across compounds that may be classified by the ASTM scheme, but are not
similar to any liquids within the laboratory reference collection. For an oxygenated
solvent to be identified, each major oxygenated compound must be identified by gas 1 2 3
Michigan State Police Grand Rapids Laboratory, 720 Fuller Ave NE, Grand Rapids, MI 49503
The Dow Chemical Company, 2030 Willard H. Dow Center, Midland, MI 48674
ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959
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chromatography retention time and mass spectral characteristics [1]. Without a
reference sample containing these compounds, a comparison of retention times cannot be performed; therefore, identification of that oxygenated solvent is not possible. If an ignitable liquid is present, but the threshold for its identification is not met, the fire
investigator does not receive information that may be probative to the investigation. This was the situation for a fire debris case in 2009, in which a fire investigator
submitted two fire debris samples from the area in which the fire originated. The fire
had self-extinguished, causing minimal damage and leaving a clearly defined origin
area. The fire was determined to have originated inside of a kitchen cabinet at or near
floor level. In the course of the fire scene examination, the fire investigator eliminated all accidental and other potential causes except for intentional activity.
Gas chromatography – mass spectrometry (GC-MS) analysis of a passive headspace
adsorption extraction of each submitted sample produced a cluster of strong peaks
(Figure 1). Initial mass spectral library searches indicated the presence of tripropylene
glycol methyl ether (TPM) (Figure 2). However, without a reference standard to which to compare the retention time and mass spectrum, an identification was not possible. An online search of ignitable liquid consumer products [2] at the time of analysis did not
yield any products containing similar components. With no reference samples containing these compounds, the samples were reported as containing no identifiable ignitable liquid residues.
In the ensuing months, information was received regarding the possible involvement of
scented oils in intentionally set and accidental fires. This information was contained
within a forwarded e-mail message that originated from an organization associated with
insurance and law enforcement. The message indicated that the scented oils are not
petroleum based, are difficult to detect in the laboratory, and are not detected by arson dogs. Pictures were included demonstrating the ignitability of several of the scented
oils. Contact with the author of the message was made, and it was determined that no chemical analysis of the scented oil products had been conducted [3].
Literature searches and discussions with ignitable liquid analysts and researchers
yielded no studies conducted in regards to the identification of glycol ethers in fire
debris samples. It should be noted, however, that one sample containing a glycol ether (a brick and stone cleaner) has been added to the online ignitable liquid consumer product database [2] since the initial casework encounter.
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Figure 1. GC-MS data of two casework samples of fire debris and of n-alkane standard.
Figure 2. Structure of tripropylene glycol methyl ether (TPM) [pubchem]
MATERIALS AND METHODS Twelve room and vehicle air fresheners with a liquid component were obtained for
analysis. An additional product (adhesive remover) was obtained from an analyst who was analyzing a case containing similar compounds. These products were labeled as
letters A through M.
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Fourteen liquids were obtained from Dow. These included 13 glycol ether reference
standards in the DOWANOL™ product line and dipropylene glycol (DPG). According to
Dow’s website [4], DOWANOL™ products are hydrophilic glycol ethers used in a broad range of applications, including coatings, cleaners, and printing inks.
Each of the 27 samples was subjected to a flame test. In addition, four liquids that may be encountered in typical fire debris samples (gasoline, charcoal lighter fluid, kerosene,
and diesel fuel) were tested in order to provide context to the flame test results. For this purpose, a cotton-tipped swab was soaked with the liquid and introduced to an open
flame. The noted observations included ignition speed, flame color, and smoke
characteristics. Table 1 displays the published flash points and classifications of the reference samples, the four additional liquids, and the consumer products.
The 27 samples were then diluted with carbon disulfide (20 µL sample added to 2 ml
carbon disulfide) and analyzed by GC-MS using the following instrument configuration and parameters:
Autosampler: CTC Analytics 4 PAL; 1.0 µL injection volume GC: Thermo Finnigan 5 Trace GC 2000; Phenomenex 6 Zebron ZB-1MS Guardian
column (30m plus 5m guard, 0.25mm inner diameter, 1 µm film); split injection (50:1) at 220°C; temperature program of 40 °C isothermal for 3.7 min, ramp
12°C/min to 100°C, ramp 25°C/min to 250°C for 1 min, ramp 25°C/min to 280°C,
isothermal for 3 min; helium carrier gas at 2.0 ml/min
MS: Thermo5 DSQ: electron ionization, full scan 30-500 m/z, 4 scans/sec The glycol ether reference standards were compared to the consumer products, and the identified components in the consumer products were added to Table 1.
Case samples were processed using a passive headspace method. The fire debris
samples were received in nylon bags or metal cans. An activated carbon strip 7 was
suspended by a wire and inserted into the headspace of each bag or can. The samples
were placed into an oven set to 80⁰C for approximately four hours and then allowed to cool to room temperature. Half of each carbon strip was eluted with carbon disulfide. The eluate was analyzed by GC-MS using the same conditions described previously.
Case samples were compared to the consumer products and reference standards.
4 5 6 7
CTC Analytics AG, Industriestrasse 20, CH-4222 Zwingen, Switzerland
Thermo Fisher Scientific, 81 Wyman Street, Waltham, MA 04254, United States Phenomenex, 411 Madrid Avenue, Torrance, CA 90501, United States
Albrayco Technologies, Inc., 38 River Road, Cromwell, CT 06416, United States
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Table 1. Information regarding the liquids in this study. Reference
DOWANOL™ Product Name
Flash Point (⁰C)
GHS# Flammable Liquid Classification Category
ASTM E1618-11 Classification>
DPM
Dipropylene glycol monomethyl ether
75†
4†
Medium Oxygenated Solvent
†
†
DPMA
Dipropylene glycol methyl ether acetate
86
4
Medium Oxygenated Solvent
DPnB
Dipropylene glycol n-butyl ether
100†
not classified†
Heavy Oxygenated Solvent
†
†
DPnP
Dipropylene glycol n-propyl ether
88
4
EPh
Ethylene glycol monophenyl ether
119†
not classified†
Medium Oxygenated Solvent Heavy Oxygenated Solvent
PGDA
1,2-Propanediol, diacetate
86†
4†
Medium Oxygenated Solvent
PM
Propylene glycol monomethyl ether
31†
3†
Light Oxygenated Solvent
†
PMA
Propylene glycol monomethyl ether acetate
46
3†
Medium Oxygenated Solvent
PnB
1-Butoxy-2-propanol
63†
4†
Medium Oxygenated Solvent
†
†
Medium Oxygenated Solvent
PnP
1-Propoxy-2-propanol
48
3
PPh
Propylene glycol phenyl ether
115†
not classified†
Heavy Oxygenated Solvent
†
†
Heavy Oxygenated Solvent
TPM
Tripropylene glycol methyl ether
121
not classified
TPnB
Tripropylene glycol monobutyl ether
126†
not classified†
Heavy Oxygenated Solvent
DPG
Dipropylene glycol
138‡
not classified†
Medium Oxygenated Solvent
Reference Liquid
Flash Point (⁰C)
GHS# Flammable Liquid Classification Category
ASTM E1618-11 Classification>
Unleaded Gasoline
-38‡
2‡
Gasoline
^
^
Kingsford Odorless Charcoal Lighter
41
3
Medium Isoparaffinic Product
Kerosene
82‡
4‡
Heavy Petroleum Distillate
‡
‡
No. 2 Diesel Fuel
80
4
Heavy Petroleum Distillate
Components (from GC-MS analysis)
ASTM E1618-11 Classification>
Reference
Consumer Product Name
A
Plug-in room freshener (Glade)
DPM
Medium Oxygenated Solvent
B
Crystal air freshener (Snuggle)
none
C
Scented oil (Elegant Expressions)
Medium Oxygenated Solvent
D
Scented oil (aromafresh)
not identified diethylene glycol monobutyl ether DPnB
E
Vehicle air freshener (Liquid Aire Xtreme)
DPMA
Medium Oxygenated Solvent
Heavy Oxygenated Solvent
F
Plug-in room freshener (febreze)
DPM
Medium Oxygenated Solvent
G
Vehicle air freshener (Refresh your car)
DPM
Medium Oxygenated Solvent
H
Vehicle air freshener (Arometrics)
DPMA
Medium Oxygenated Solvent
I
Vehicle air freshener (Fragrance Pendant)
DPG
Medium Oxygenated Solvent
J
Scented oil (Home Essense)
DPG
K
Plug-in room freshener (Air Wick)
DPM and TPM
L
Plug-in room freshener (Yankee Candle)
DPM
Medium Oxygenated Solvent Medium/Heavy Oxygenated Solvent Medium Oxygenated Solvent
M
Solvent (Goo Gone Painters Pal)
TPM
Heavy Oxygenated Solvent
#: Globally Harmonized System of Classification and Labeling of Chemicals by Society for Chemical Hazard (http://www.schc.org/pdf/fact_sheets/SCHC_GHS_FS2_Flammable_Liquid.pdf, accessed 12/28/2012) > : Ref [1]. Due to overlapping ranges of subclasses in E1618-11, the subclass designations used in this table correspond to the following n-alkane ranges: Light: C 13 † : Information from Material Safety Data Sheet (MSDS) provided by Dow ‡ : From Sigma-Aldrich MSDS (http://www.sigmaaldrich.com/safety-center.html, accessed 12/28/2012) ^ : From The Clorox Company MSDS (http://www.thecloroxcompany.com/downloads/msds/charcoalproducts/kingsfordodorlesscharcoallighter.pdf; accessed 12/28/2012)
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RESULTS All of the glycol ether reference standards ignited and supported a flame, but varied in how quickly they ignited. This confirms that, if identified in fire debris samples, these compounds can be described as ignitable. The flame test observations of most of the reference standards were generally similar to flame test observations of kerosene or diesel fuel.
Eleven of the 13 consumer products ignited and supported a flame (see Table 2). The
flame test results did not always correspond between the consumer products and the components identified in those products. Notably, one of the products (Goo Gone
Painters Pal) did not ignite even when held in a flame despite containing a component (TPM) that does ignite and support a flame. This product was not miscible in diethyl
ether or carbon disulfide, indicating that it was aqueous. These results demonstrate that the ignitability of the products may be influenced by other components. A searchable
consumer product website [5] demonstrated that at least one of the other tested glycol ethers (DPM) is present in some aqueous products (e.g., StoneTech Stone and Tile Cleaner).
The glycol ether reference standards contained either a single peak or multiple peaks in
a narrow retention time window (Figures 3A and 3B). The retention times for these
samples were between the retention times for n-alkanes C 6 -C 15 ; therefore, they could be described as light, medium or heavy oxygenated solvents. The mass spectra varied
from sample to sample, but some ions were present in multiple samples (Figures 4A and 4B). Some of the prominent ions among the samples included m/z 43, 45, 57, 59, 73,
87, 89, 94, 101, 103, and 117. Because of the differing chemical structures among the
reference standards, a variety of prominent ions can be expected. Although not present
in all of the samples, the m/z 59 ion may be useful as a diagnostic peak for some glycol ethers. Additional work elucidating the formation of the ions was not conducted.
Eleven of the consumer products could be correlated to five of the reference standards
based on the presence of components with similar retention times, overall appearance of chromatographic patterns, and mass spectral characteristics. The Air Wick brand
room freshener displayed peaks corresponding to both dipropylene glycol methyl ether
(DPM) and TPM, demonstrating that mixtures of glycol ethers may be encountered from
a single product. One consumer product (Elegant Expressions scented oil) contained an apparent glycol ether (diethylene glycol monobutyl ether) that was not among the
reference standards in our collection. The remaining consumer product (Snuggle crystal air freshener) had no components similar to the reference standards and was not
ignitable. Most of the consumer products contained additional peaks that were not further characterized in this study. These peaks may be useful, however, for
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comparisons of fire debris samples and reference liquids for sourcing or associative
purposes. Figures 5-10 demonstrate the similarities in chromatographic and spectral data observed between the consumer products and the reference standards. Table 2. Flame test results for the liquids in this study. Reference
DOWANOL™ Product Name
DPM
Dipropylene glycol monomethyl ether
DPMA DPnB
Dipropylene glycol methyl ether acetate Dipropylene glycol n-butyl ether
Flame test results ignition speed*
color
smoke
medium
orange/yellow
none
medium
orange/yellow
none
medium
orange/yellow
none
orange/yellow
none
DPnP
Dipropylene glycol n-propyl ether
medium
EPh
Ethylene glycol monophenyl ether
slow
orange
heavy
PGDA
1,2-Propanediol, diacetate
slow
orange/yellow
none
PM
Propylene glycol monomethyl ether
medium
orange/yellow
none none none
PMA
Propylene glycol monomethyl ether acetate
fast
orange/yellow
PnB
1-Butoxy-2-propanol
orange/yellow
PnP
1-Propoxy-2-propanol
fast fast
orange/yellow
none
PPh
Propylene glycol phenyl ether
slow
orange
heavy
TPM
Tripropylene glycol methyl ether
orange/yellow
none
orange/yellow
none
orange/yellow
none
TPnB
Tripropylene glycol monobutyl ether
slow slow
DPG
Dipropylene glycol
slow
Flame test results
Reference Liquid
ignition speed*
color
smoke
Unleaded Gasoline
fast
orange/yellow
moderate
Kingsford Odorless Charcoal Lighter
fast
orange/yellow
moderate
medium
orange/yellow
moderate
slow
orange/yellow
heavy
Kerosene No. 2 Diesel Fuel Reference
Flame test results
Consumer Product Name
color
smoke
orange/yellow
A
Plug-in room freshener (Glade)
ignition speed* medium
B
Crystal air freshener (Snuggle)
none
N/A
moderate N/A
C
Scented oil (Elegant Expressions)
slow
orange/yellow
none
D
Scented oil (aromafresh)
medium
orange/yellow
none
E
Vehicle air freshener (Liquid Aire Xtreme)
fast
orange/yellow
heavy moderate
F
Plug-in room freshener (febreze)
fast
orange/yellow
G
Vehicle air freshener (Refresh your car)
medium
orange/yellow
heavy
H
Vehicle air freshener (Arometrics)
medium
orange/yellow
moderate moderate
I
Vehicle air freshener (Fragrance Pendant)
slow
orange/yellow
J
Scented oil (Home Essense)
slow
orange/yellow
none
K
Plug-in room freshener (Air Wick)
medium
orange/yellow
heavy
L
Plug-in room freshener (Yankee Candle)
medium
orange/yellow
heavy
M
Solvent (Goo Gone Painters Pal)
none
N/A
N/A
*: Relative speed at which the liquid started to burn. "Fast" indicates the flame started and continued burning at approximately the same height; "Medium" indicates the flame started low and gradually increased in height; "Slow" indicates the flame started only after holding in the burner's flame for a short time.
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Figures 3A (top) and 3B (bottom). Chromatograms of reference standards.
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Figures 4A (top) and 4B (bottom). Mass spectra of selected peaks from reference standards.
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Figure 5. Consumer products A, F, G, and L; reference standard DPM
Figure 6. Consumer products E and H; reference standard DPMA
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Figure 7. Consumer product D; reference standard DPnB
Figure 8. Consumer products I and J; reference standard DPG
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Figure 9. Consumer product M; reference standard TPM
Figure 10. Consumer product K; reference standards DPM and TPM
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Glycol ethers have been encountered in eight fire debris cases in the authors’ laboratory in the three years since learning of these products. Two of these comparisons are
displayed in Figures 11 and 12. Seven of the cases involved dipropylene glycol n-butyl ether (DPnB) and one case involved TPM. In addition, DPM was encountered in an
atmosphere control sample that was collected after the floor of the evidence processing room had been refinished. The attribution of DPM to this product (U.S. Chemical, Misco
Genesis GX-2003 High Speed Floor Finish) was verified by consulting its label and MSDS.
Figure 11. Fire debris case A, Items 1 and 2; reference standard DPnB
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Figure 12. Fire debris case B, Items 1 and 2; reference standard TPM; consumer product M
DISCUSSION This paper informs fire debris analysts of a new category of oxygenated solvents –
glycol ethers – that may be encountered when processing fire debris using a passive
headspace adsorption method with parameters typically employed in recovering and
analyzing ignitable liquid residues. Several consumer products containing these solvents were located. By recognizing these compounds and comparing them to reference
standards or available consumer products with known components, the identification of glycol ethers in fire debris samples becomes possible. A library of the mass spectra
produced from the reference standards has been added to the searchable library list at the authors’ laboratory. This library has proven successful in generating hit lists with appropriate glycol ethers at the top when searching fire debris sample peaks
corresponding in retention time and chromatographic pattern to the reference standards.
One of the purposes of the fire debris analyst’s report is to provide information to a fire investigator that is attempting to determine the cause of a fire. The presence of
ignitable liquid residues in a fire debris sample may indicate an intentionally set fire. Alternatively, there may be legitimate reasons an ignitable liquid was present at the
scene of a fire [6]. Because of the intended uses of the consumer products examined in
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this study, it would not be unusual for glycol ethers to be present as residues at a house or vehicle fire. However, because of their ignitability, the possibility exists for the intentional use of products containing glycol ethers to start or spread a fire.
It should be recognized that the ignitability of the glycol ether-containing products may
be influenced by other components, which may or may not also be identified in the
report. According to information from their MSDSs [4], four of the tested glycol ethers
(DPM, PM, PnP, and TPM) are 100% soluble in water at 25˚C; the remainder have water
solubilities ranging from 2% (PPh) to 19% (PMA). One of the products (Goo Gone Painters Pal) was not ignitable and was likely aqueous. The floor finish that contained DPM was aqueous. It would be expected that some of these glycol ethers are present in other aqueous, non-flammable household products. Their solubilities in water would also
impact their likelihood of detection if water was used for fire suppression.
In order to provide context to the fire investigator, a statement in the report that offers
some possible sources of glycol ethers may be included, such as, “Consumer products
that contain this category of oxygenated solvents include but are not limited to some
scented oils used in home and vehicle air fresheners, some paint and adhesive solvents, and some household cleaning and maintenance products. It should be noted that some of these consumer products are ignitable and some are not ignitable.”
Based on the number of recent submissions containing a glycol ether and the ignitability
of some of the products containing these compounds, it is conceivable that these
compounds, or mixtures thereof, may produce fire patterns that cause a fire investigator to suspect that an ignitable liquid may have been used. This may be particularly true
when the fire origin is clearly defined. The identification of a glycol ether in a fire debris sample may help explain the appearance of the fire scene and aid in the fire
investigator’s assessment regarding whether the fire under investigation was intentionally set or accidental. ACKNOWLDGEMENTS The authors would like to thank their employer for allowing the time necessary to complete this project. Thanks go to Christopher Dean for providing fire investigation perspective and to Dow for supplying the reference samples. DOWANOL™ and Dow are registered trademarks of The Dow Chemical Company. REFERENCES 1. ASTM E1618-11, Standard Test Method for Ignitable Liquid Residues in Extracts from Fire Debris Samples by Gas Chromatography – Mass Spectrometry
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2. http://ilrc.ucf.edu (accessed 10/30/2009 and 09/24/2012) 3. Personal communication with Tony Capozzi, insurance investigator 4. http://www.dow.com/products/product-line/dowanol/ (accessed 09/24/2012) 5. http://householdproducts.nlm.nih.gov/index.htm (accessed 04/01/2013) 6. Stauffer E, Dolan J, Newman R, Fire Debris Analysis, 2008, Elsevier, Burlington, MA.
Page 32 of 42
THE MICROSCOPE
•
Vol. 61:2, pp 51–60 (2013)
Plumbum Microraptus: Definitive Microscopic Indicators of a Bullet Hole in a Synthetic Fabric* Christopher S. Palenik1, Skip Palenik1 Microtrace, LLC Peter Diaczuk2 John Jay College of Criminal Justice and the CUNY Graduate Center
KEYWORDS Ammunition, backscattered electron imaging, bullets, energy-dispersive X-ray spectroscopy, fabrics, fibers, firearms, forensic science, Fourier transform infrared microspectroscopy, lead, primer gunshot residue, polarized light microscopy, secondary electron imaging, scanning electron microscopy ABSTRACT A central question in a criminal forensic investigation involved a hole (later termed a “defect”) observed in a garment and whether it was produced by a bullet or some other means. The individual wearing the item was known to have fired or been in the vicinity of a firearm that was discharged, rendering the presence or absence of gunshot residue on the garment irrelevant. The micromorphology and elemental composition of the severed fiber ends in a series of exemplar bullet holes were characterized to identify specific physical indicators of the bullet-garment interaction on a microscopic scale. This study confirms prior research indicating that fiber failure, due to the highenergy transfer from a bullet to a synthetic fabric, is consistent with a high-speed tensile fracture mechanism, which results in characteristic fiber-end micromorphology due to partial melting. In addition, scanning electron microscopy (SEM) imaging and elemental analyses by energy-dispersive X-ray spectroscopy (EDS) provide direct evidence of the capture of detectable microscopic lead particles both on and within the
melted fiber ends, a process termed here as plumbum microraptus (microscopic lead capture). These lead particles are observed primarily as planar abrasion fragments but also as spherical particles, the latter of which further illustrates the high-energy transfer. Through the study of individual broken fibers from within a suspected bullet hole, these characteristic indicators provide a minimally invasive and direct means to definitively associate or (equally important) dissociate a fabric defect with a bullet perforation. INTRODUCTION The question of whether or not a bullet has perforated a fabric is a discrete question with relevance to the field of forensic science. In many instances, the presence of secondary evidence such as blood, tissue or an associated wound can render such a question trivial. In close range events, the presence of primer gunshot residue (pGSR) on a fabric can provide strong evidence of a ballistic association. At greater distances, a dark ring of debris, called “bullet wipe,” is often observed (Figure 1) or can be detected (even on dark clothing) and has been stated to consist of traces of bullet metal, lubricant and residue from the gun barrel (1, 2) (Figure 2). In some cases, bullet wipe may not be visible or the presence of pGSR on a garment may not be sufficient to provide a definitive answer as to the origin of a particular hole. For example, in the event that an alleged bullet hole was located on a garment worn by a person who fired or was in the vicinity of a discharged firearm, such ancillary evidence may not be
* Originally presented at Inter/Micro 2011, Chicago. 1 790 Fletcher Drive, Suite 106, Elgin, IL 60213;
[email protected] 2 524 W. 59th Street, New York, NY 10019;
[email protected] Page 33 of 42
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Photo courtesy of Peter Diaczuk
Photo courtesy of Peter Diaczuk
Figure 1. This hole in a woven cotton fabric was made by a 7.62 mm full metal jacket bullet. The discoloration at the perimeter of the hole is an example of “bullet wipe,” the deposition of bullet and barrel material transferred as the bullet perforated the fabric. Shown is the entry side of the hole, which has the greatest concentration of deposited material and can be more closely examined microscopically to assess fiber failure mechanisms and spectroscopically to identify the foreign material. The presence of lead can also be determined at such a site by using the classic sodium rhodizonate test. Each line on the scale equals 1/16 inch.
conclusive. In such cases, we have demonstrated that a direct microscopical examination of the hole, often termed the “defect area” (in contrast to the area surrounding the hole), can provide a definitive answer to this question. This approach is based on a fundamental principle of forensic science, which suggests a strong likelihood of transfer between objects that come into contact with each other. In the case of a bullet that perforates a synthetic fabric, at least two possible types of transfer are hypothesized to occur at the interface of the bullet and fabric. The first is a transfer of energy, which results in fiber (and fabric) failure; the second is a transfer of material from the bullet to the broken ends of the fibers (or the transfer of polymer to the bullet). The energy transfer resulting in high-speed synthetic fiber breakage, due to an event such as a bullet perforation, has been mechanically classified as a “high-speed tensile break” (3) or “rapid shear.” Physically, such a break can be understood by considering the brief interaction of a fired bullet as it passes through a synthetic fabric whereby a portion of the kinetic en-
Figure 2. Gases shown were emitted at the muzzle of an AK-47 rifle one millisecond after the bullet exited the barrel. This plume contains a rich supply of lead, which originates from both the primer (containing lead styphnate) and the base of the bullet that is not enclosed by the jacket, thus exposing the lead core (seen in Figure 3) to the hot gases impinging on the base. When the firing sequence begins, the firing pin strikes the primer, creating a shower of sparks that ignites the smokeless powder, which burns rapidly, generating a huge volume of hot gas. Some of the exposed lead is vaporized by the hot gases impinging on the base of the bullet and results in the heavy contribution of lead in the plume exiting the muzzle. A portion of this vaporized lead is left behind in the barrel and condenses inside the barrel circumference when the temperature cools, so when the next bullet travels down the barrel it can carry with it lead from prior discharges.
ergy is transferred from the bullet to individual fibers of the fabric. This tension mechanism stretches and eventually breaks the fiber. The energy transfer is sufficient to melt the stretched portion of the thermoplastic polymer comprising the fiber. This result has been observed in several forensic research efforts specifically involving the perforation of synthetic (nylon or polyester) textiles by a bullet (4, 5). This mechanism does not apply to cellulose-based fibers such as cotton or rayon, which do not melt (6). It is also anticipated that particle transfer will occur during the bullet-fiber contact period, resulting in the presence of firearms-related particles around this area and embedded in the molten fiber. While SEM/ EDS and atomic absorption spectroscopy have been used to identify lead (Figures 3 and 4) and primer particles (Figure 5) in the vicinity of bullet holes (7), it is hypothesized that such particles will also be found on and embedded within the broken fiber ends. Although the distinction between “around” and “embedded within” is minor, the latter provides definitive evidence that the fiber end was created by a high-speed lead or lead-laden object and eliminates the argument of in-
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Photo courtesy of Peter Diaczuk
Figure 3. A full metal jacket bullet that was removed from a 7.62 x 39 mm cartridge has been cut in half lengthwise to reveal its construction. Despite the name “full metal jacket,” the base of the bullet is not jacketed and, therefore, the exposed lead is susceptible to attack by the energetic gases generated by the burning propellant. These gases impinge upon the exposed lead, some of which is volatilized, allowing it to migrate to the outside surface of the bullet’s jacket; it can also condense on the inside of the gun barrel. This lead becomes one source of material that can be deposited at the perimeter of a bullet hole. (Scale is in millimeters.)
Photo courtesy of Peter Diaczuk
Figure 4. Two unfired 7.62 mm soft-point bullets, one is base up (left) and the other is base down (right). The base-up bullet reveals that the jacket material continues around the bullet’s base, sealing off the lead core. The base-down bullet shows that the jacket does not extend fully to the tip, leaving exposed lead to interact with the object that the bullet impacts (therefore, the name “soft point” bullet). Similar to the mechanism described in Figure 3, this lead becomes one source of material that can be deposited at the perimeter of a bullet hole. (Scale is in sixteenths of an inch.)
advertent contamination from non-GSR sources, e.g. airbags (8), fireworks (9), brake pads (10), etc. Confirmation of this hypothesis in conjunction with the distinct fiber-end morphology, as demonstrated in this research, provides a simple and definitive means to confirm or refute the statement that a hole was produced by a bullet using microanalytical methods readily available in most forensic laboratories. EXPERIMENTAL
Photo courtesy of Peter Diaczuk
The bullet holes were initially examined by stereomicroscopy with Leica EZ-4D and Wild M5 stereomicroscopes using a combination of transmitted, oblique and co-axial illumination. Isolated individual fibers were mounted on glass microscope slides in various refractive index oils (n=1.520 and n=1.660 at 20° C). The preparations were then examined by transmitted polarized light microscopy using an Olympus BH2 microscope. Fibers were mounted on carbon tabs on aluminum stubs, which were then gold-coated for SEM analysis. SEM analysis was conducted using a JEOL 6490LV SEM with a Thermo Noran System Six Silicon Drift Detector at 20keV with a spot size that varied from 20 to 65 (nominal value) with backscattered electron (BSE) and secondary electron (SE) imaging detectors.
Figure 5. Ammunition primer removed from an unfired cartridge is shown intact on the right. A similar primer is disassembled to reveal its two main components, the anvil (left) and the cup (center). The yellow mustard color is a result of the lead styphnate initiator. When struck by the firing pin, the impact-sensitive composition is crushed between the inside of the cup and the anvil, igniting it and sending a shower of sparks into the body of the cartridge to then ignite the smokeless powder. These sparks contain combustion by products of the lead styphnate, thus contributing lead to the system. Even if the jacket seals off the lead core of the bullet (as in Figure 4), the lead contribution from the primer will present a source of lead that can be carried with the bullet to the impact site. (Scale is in millimeters.)
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Photos courtesy of Christopher S. Palenik, Microtrace, LLC
Figure 6. The entry (6A) and exit (6B) sides of a single-bullet perforation in a cotton-polyester blended fabric. The entry side (6A) shows a ~2 mm wide annular discoloration that surrounds the hole, which is generally referred to as “bullet wipe.”
Exemplar Preparation An exemplar fabric containing multiple entry and exit points was prepared for this examination by firing Wolf ammunition (7.62 x 39 123 GR. SP, steel jacketed, lead bullet) from an AK-47 rifle at a distance of 3.5 meters normal to the target at an air temperature of 30° C through a 70% cotton and 30% polyester (polyethylene terephthalate) dyed sweatshirt fabric. The fiber composition was confirmed by polarized light microscopy (PLM) and Fourier transform infrared microspectroscopy (FTIR) (6). The entry and exit side of one bullet perforation in the fabric is shown in Figure 6. The entry side of the hole (Figure 6A) shows a ~2 mm wide annular discoloration or staining that surrounds the hole, which is generally referred to as “bullet wipe” (4). Stereomicroscopy was used to determine and document the size of the holes (~0.5 cm), their relatively round shape and to observe a distinct directionality imparted to the broken threads, which are consistent with, though not definitively indicative of, the direction of bullet travel. (Fiber direction may vary in many cases due to removal of clothing and other factors.)
the sample and details of the case, specimens can be prepared in a variety of ways. For SEM, the simplest method is to excise a 2.5 x 2.5 cm fabric square containing the hole in question. In this way, it is possible to study an entire hole in the SEM. The drawbacks of this method are that the broken fibers are not ideally oriented in a direction that is optimal for imaging their ends, and in forensic casework, isolation of an area of this size is not generally an option due to evidence preservation requirements. For these reasons, single fibers were individually isolated and studied. A single fiber of interest was located under the stereomicroscope and held with a pair of forceps approximately 5 mm from the broken tip (taking care not to touch the broken end). Prior to cutting off the thread from the garment, the fiber to be excised was marked (~10 mm from the broken tip) using a fine-tipped permanent marker while observing under a stereomicroscope. A cut was then made through the marker line, effectively isolating the fiber of interest. A benefit to this method is that the freshly cut ends (both that on the isolated fiber and the end remaining in the fabric) are both marked providing a semi-permanent indicator of the cut ends. This ensures that any future analysis is not confused by razor-cut fiber ends.
Fiber-End Isolation and Preparation Once located by stereomicroscopy, a more detailed analysis of the frayed fibers was conducted at higher magnification by PLM and SEM. Prior to this, it was necessary to isolate individual fibers for analysis while tracking the end formed by the bullet. Depending on
Fiber-End Characterization Characterization of the isolated fibers by PLM was conducted using temporary mounts in refractive index oil (n=1.520). In this way, the generic class of the fiber can be easily identified by its optical properties (6) and, if necessary, washed in xylene, dried and
RESULTS AND DISCUSSION
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Photos courtesy of Christopher S. Palenik, Microtrace, LLC
Figure 7. 7A: A stereomicroscope image shows yarn composed of multiple fibers that were all severed by the bullet perforation. The red circle highlights a group of fibers that were fused together as a result of the high-energy transfer that occurred during perforation. 7B: A transmitted light image of a broken polyester fiber end shows the characteristic globular end resulting from a high-speed tensile fracture mechanism. 7C and 7D: Multiple fiber ends observed in secondary electron imaging; 7C shows fused fiber ends. 7D: The result of a stretch, fracture and recoil due to a high-speed, high-energy fiber break are captured in the morphology of a broken fiber end.
mounted for SEM analysis (though care should be taken with respect to fiber orientation because xylene will dissolve the orientation mark on the fiber). SEM analysis was performed in various configurations using a JEOL 6490LV tungsten SEM. Uncoated fibers were successfully examined via backscattered electron imaging in variable pressure mode at 5–20 kV (30–50 Pa). While serviceable, fibers still charged at times under these conditions make the highest quality documentation difficult. For the purposes of publication, fibers were gold coated and observed without issue in both BSE and SE imaging modes. The gold coated fibers were generally preferable for study, documentation and elemental analysis. Despite the thin
gold coating, metallic particles of interest (e.g. lead, chromium, iron etc.) were easily located in BSE imaging and readily characterized by EDS (as demonstrated here). Morphology Indicators of high temperature alteration are visible even at relatively low magnifications obtainable by stereomicroscopy, such as the fusing of multiple fibers shown in Figure 7A. In Figure 7B, the bulbous end typical of a severed fiber resulting from the rapid shear mechanism is shown as observed by PLM. Based on the failure mechanism, which results in partial melting and recoil of the elongated fiber prior to cooling, this characteristic end morphology has been
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Figure 8. A SE-SEM image of a single severed yarn shows numerous polyester ends (circled) all of which have globular ends characteristic of a high-speed, high-energy fracture mechanism. Arrows point to broken cotton fibers, which do not have globular ends.
Photo courtesy of Christopher S. Palenik, Microtrace, LLC
termed a “globular” end. In general, the globular ends of the fibers show remarkably decreased birefringence when observed between crossed polarizers, which are consistent with prior findings (4, 5). This is expected, due to the loss of orientation when the newly formed fiber ends melt and rapidly cool without any specific means of reorientation. While indications of globular ends can be observed by PLM, secondary electron imaging in the SEM provides more definitive evidence of the melting, stretching and rebounding that occurs when a thermoplastic fiber undergoes rapid shear. Figure 7C shows the melted globular ends of several fibers. In Figure 7D, the stretch, fracture and recoil resulting from a high-speed, high-energy fiber break are captured in the morphology of a broken fiber end as illustrated by the roughly annular compression marks near the globular end. Cotton (and other cellulosic) fibers do not melt and would not be expected to show such features, which are characteristic of a thermoplastic fiber. However, such fibers, which are often blended with synthetics in a fabric, are readily identified by PLM or SEM by their optical properties and morphology. A SE-SEM image of a single, entirely severed thread (composed of many twisted fibers) isolated from the bullet hole is shown in Figure 8. Examination of this
particular thread by stereomicroscopy, PLM and SEM shows that all of the broken polyester fiber ends in this cluster are globular. In total, more than 90% of the severed synthetic fiber ends counted in these bullet holes show distinct globular ends. Particle Transfer By transmitted light, visible discoloration in the form of dark opaque debris on the severed fibers in the bullet hole is apparent (Figure 7B). By reflected light, these same fragments show a dull metallic luster, which is consistent with the appearance of fine lead particles. This surface debris has a more irregular particle size distribution and is clearly distinguishable from the smaller, transparent TiO2 inclusions that are added to many synthetic fibers as a delustrant. Because it was anticipated that these metallic particles were related to bullet lead, they were studied by BSE imaging. Figure 9A shows the distribution of lead particles on the severed fiber end where lead-rich particles are indicated by their high contrast (white) against the lower average atomic number of the fiber and background of the image. Elemental analysis by EDS confirms that all of these particles are lead-rich. Figure 9B shows one particle that contains additional detectable iron and chromium, indicating it is a stainless steel particle.
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Figure 9. 9A: A BSE-SEM image shows the distribution of lead-rich particles on a broken polyester end. 9B: EDS spectrum of one of these particles also shows the presence of iron and chromium, suggesting the presence of stainless steel. The gold peaks are a result of the coating applied to improve image resolution.
Photos courtesy of Christopher S. Palenik, Microtrace, LLC
Figure 10. SE-SEM images show 10A, lead plates abraded from the perforating bullet and 10B, a lead sphere resulting from aerosol deposition of molten lead. Both types of particles have similar elemental compositions.
Detailed examination of lead particles on these fiber surfaces show that most of them are platy or planar abrasion particles (Figure 10A), while occasional spherical particles are also observed (Figure 10B). Such spheres originate when molten lead cools and solidifies in air to a low surface energy (spherical) morphology. Both the spheres and plates have a similar elemental composition and are composed of lead, with minor antimony and copper (Figure 11). This composition is typical of a bullet lead alloy. None of the particles studied showed evidence of tri-component pGSR
(Pb-Ba-Sb) particles (11). The presence of fused fibers is shown at relatively low magnification in Figure 7A. The fusing of fibers, which was often observed among the fibers in each bullet hole studied, is shown in more detail in Figure 12. Detailed examination of these images shows two fused fibers at a variety of magnifications, which illustrate the extent of the fusing and the distribution of GSR particles on their surface. While lead particles are generally present in higher concentrations at the globular end of the fibers (and qualitatively decrease
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Figure 11. A typical EDS spectrum from a lead particle on the end of a severed fiber.
in number as the distance from the severed end increases), they are also present in high concentrations at the melted interface of the two fused fibers (Figure 12B and 12C). Examination of one of the fused areas also show that not only are the lead particles present on the surface of the fiber, but that they are also trapped within the fused areas, as confirmed by EDS and illustrated visually in the combined BSE/SE image shown in Figure 12D. These images illustrate the irrefutable link between a high-energy transfer and a lead-rich particle transfer, which can only originate from a ballistic event involving a lead or lead-laden projectile. SUMMARY AND FORENSIC SIGNIFICANCE These results indicate that a bullet hole from a jacketed soft point (exposed lead) bullet fired through a synthetic fabric can be definitively identified by studying the severed broken ends within a hole to identify the presence of globular ends and the presence of adhering and/or embedded lead particles. Under certain circumstances, the issue may be raised as to whether certain variables may affect the formation or residence time (persistence) of the characteristic features noted above. Such variables may include environmental factors (such as weather), handling factors, fiber type, ammunition type, speed and firing distance. Because the physical indicators of bullet perforation established above are subject to unknown and potentially disputed environmental variables (e.g. handling, washing, storage conditions and cross con-
tamination) or firing variables (e.g. ammunition type and velocity), questions of persistence (i.e. residence time) will arise, particularly due to the similarities in particle size and composition shared by GSR. For example, a wealth of research into the affects of environmental conditions on the residence time of GSR particles has been conducted (11, 12) and many laboratories limit the collection of GSR to 24 hours or less after an incident due to concerns over residence and background contamination that may occur over longer periods (12). However, GSR is deposited by a distinctly different mechanism than metallic bullet fragments being transferred to severed fibers in a bullet hole. GSR is deposited on a surface at ambient conditions, while metallic ammunition particles transferred during partial melting of the fiber end are partially or entirely embedded into the fiber surface. This singular difference illustrates why metal particles associated with a bullet hole will have a distinctly longer residence time, regardless of handling conditions. Similarly, the characteristic globular ends are part of the fabric and are, therefore, not subject to any degradation beyond that expected for the garment as a whole. At ~20 μm in length, the globular end represents only a minor fraction of the total fiber length, which is generally at least 100x longer and physically anchored in the fabric. Therefore, both indicators of bullet perforation are expected to persist through harsh post-firing conditions. While the exemplar in this work is composed of polyester fibers, many other types of fibers are used in the textile industry (e.g. nylon, polyolefin and rayon).
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Photos courtesy of Christopher S. Palenik, Microtrace, LLC
Figure 12. 12A: An SE-SEM image shows two fibers that were thermally fused during the high-speed impact event. 12B: Close-up view of the area denoted by an arrow in part (12A) showing the presence of lead particles on the fused fibers (SE-SEM). 12C: Highest magnification image of the same fused fibers at the melted interface showing individual, discrete lead particles abraded from the bullet during impact (SE-SEM). 12D: Mixed SE-BSE SEM image shows that lead particles are actually embedded within the melted polymer (arrow).
The mechanism of high-energy tensile fracturing also occurs in other thermoplastic fibers such as nylon to produce similar globular ends (5). In contrast, cellulosic fibers (e.g. cotton, rayon and vegetable fibers) will not melt and, therefore, do not form globular ends. SEM examination of cotton fibers in our research confirms this (Figure 8), however, metal particles of lead were observed on the surface of the severed cotton fibers as well. Ammunition type is another factor that will vary in casework. Ammunition and its jacketing are manufactured with various compositions. The detection of multiple metals on the globular ends by EDS in this work suggests that metals from bullets of different com-
positions and from different parts of the ammunition hold the potential to be transferred to a severed fiber. Conversely, the observation of specific lead alloys, GSR particles, copper, brass, stainless steel or other components can provide additional investigative information about the source of the impacting bullet. Finally, the question of globular end formation may be challenged. The mechanism of globular end formation is directly related to the kinetic energy of the bullet passing through the fabric, which in turn is related to the velocity of the bullet. A prior study of globular ends produced in polyester and nylon fibers correlated to chronographed bullet velocities showed that various combinations of firearms and ammuni59
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tion used to obtain velocities, ranging between 40 m/s and 823 m/s, all resulted in the production of globular ends (5). Microscopic features suggestive of other sources of fabric defect formation (e.g. “pinching” from scissors, tool marks from razor cuts, etc.) have also been studied (3) and have been shown to be different from those created by a bullet. Therefore, in addition to proving a positive, the question may arise in certain contexts as to whether absence of such features can be used to state that a fabric “defect” was not produced by a bullet. Based on this research, both globular end formation and metallic particle capture would be expected to occur under all but the most extreme conditions. Therefore, it follows that the absence of such indicators is strongly suggestive of a negative conclusion — i.e. a bullet did not produce the hole. ACKNOWLEDGEMENTS The authors would like to thank Jason Beckert and Brendan Nytes of Microtrace, LLC for discussions and comments during the course of this research. REFERENCES 1. J.A. Bailey. “Analysis of Bullet Wipe Patterns on Cloth Targets,” Journal of Forensic Identification, Vol. 55, No. 4, pp 448–460, 2005. 2. P.R. DeForest, L. Rourke, M. Sargeant and P. A. Pizzola. “Direct Detection of Gunshot Residue on Target: Fine Lead Cloud Deposit,” Journal of Forensic Identification, Vol. 58, No. 2, pp 265–276, 2008. 3. J. Hearle, B. Lomas and W. Cooke, Eds. Atlas of Fibre Fracture and Damage to Textiles, 2nd ed., The Textile
Institute, CRC Press, Woodhead Publishing Limited, 1998. 4. L. Haag, in Shooting Incident Reconstruction, Elsevier Academic Press, pp 37–39, 2006. 5. C. Huemmer. “The study of rapid shear in synthetic fibers from ballistic impact to fabrics using polarized light microscopy” (MS thesis), John Jay College of Criminal Justice, City University of New York, 2007. 6. S. Palenik. “Microscopical Examination of Fibres,” in Forensic Examination of Fibres, 2nd ed., J. Robertson and M. Grieve, Ed., Taylor and Francis: London, pp. 153–178, 1999. 7. M. Raverby. “Analysis of Long-Range Bullet Entrance Holes by Atomic Absorption Spectrophotometry and Scanning Electron Microscopy,” Journal of Forensic Sciences, Vol. 27, No. 1, pp 92–112, 1982. 8. R. Berk. “Automated SEM/EDS Analysis of Airbag Residue I: Particle Identification,” Journal of Forensic Sciences, Vol. 54, No. 1, pp 60–68, 2009. 9. P. Mosher, M. McVicar, E. Randall and E. Sild. “Gunshot Residue-Similar Particles Produced by Fireworks,” Canadian Society of Forensic Science Journal, Vol. 31, No. 2, pp 157–168, 1998. 10. C. Torre, G. Mattutino, V. Vasino and C. Robino. “Brake Linings: A Source of Non-GSR Particles Containing Lead, Barium and Antimony,” Journal of Forensic Sciences, Vol. 47, No. 3, pp 494–504, 2002. 11. ASTM E1588 – 10e1. Standard Guide for Gunshot Residue Analysis by Scanning Electron Microscopy/Energy Dispersive X-ray Spectrometry, ASTM International: West Conshohocken, PA. 12. R. Berk, S. Rochowicz, M. Wong and M. Kopina. “Gunshot Residue in Chicago Police Vehicles and Facilities: An Empirical Study,” Journal of Forensic Sciences, Vol. 52, No. 4, pp 838–841, 2007.
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