ELSBVIER 40-41 (1997) 3-i9

Forensics, fakes, and failures: pyrolysis is one part in the overall armoury’

Roy S. Lehrle *

Pyrolysis methods are only one s&ion of the tide range of techniques which are currerttiy bciig used to investigate forensic samples in poke work. fakes in art and archaealugy. and failures in functional industrial components. Other methods in&de direct chromatography and mass spectr~metric methods, UV and IR methods. optical sod ekctnm micnwcopy, X-ray methods, isotope and tberrnolumin-t dating, biochemical methwls, and pattcrnl style analysis. (This lilt is by no means exclusive). Some contributions from pyrolysis 8.2 outlined, and also the principles underlying some of the other clKrcnt invl%stigstive fne&ods are reviewed. Specific examples arc provided to illustrate the scope of some of the wthods. Finally, details of a case history are discussed, where detective work involving pyrolysis methods has beer involved. Q 1997 Elsevier Science B.V.

Keywurdr: Failures; Fakes: Forensics

Forensic problems, detecting fakes, and fmding the reasons why components have failed, are all very demanding for the following reasons: 1. The quantities of material available may be very small indeed, the samples may

be impure, and can pose new microanalytical problems. 2. There is pressure to use non-destructive methods wherever possible 3. Any false trails or incorrect conclusions in the scientific work done on the

samples can result in the failure of prosecutions, or (even more important) the

??Tel: +44 21 414444Q far: +44 21 4144403. I Paper pmentcd at the Pyrolysis ‘% Conferma. Vcti. 19%.

0165~2370/97/517.00 0 1997 Elscvicr Science B.V. AU tights mw~cd. P~~SOl65-2370(97)00021-I

4 R.S. LPhrk/J. Anal. Appl. Pyrolysis 40-41 (1997) f-19

conviction of innocent people. At the very least there may be some unwarranted slur on the reputation of a person or a manufacturer. Although scientists who work in these areas may therefore be somewhat daunted by the difficulties and responsibilities imposed by these factors, these may be compen- sated by the satisfaction which comes when it proves possible to solve a really challenging problem!

In this paper, examples are given of sume of the many techniques which are being applied to such studies, with some indication of the basic principles underlying them. A case history will then be described in greater detail, and finally there will be some mention of the social implications of this area of science.

2. Some investigative teci&nres

This paper clearly cannot set out to review all of the techniques which are, or have been, applied to investigate forgeries, failures, and forensic samples. The truth of the matter is that any problem in these areas may pose a very basic research challenge, and any technique from the whole armoury of science, or better any combination of such techniques, may be brought to bear on the problem. Within the space available, the present objective is to illustrate that pyrolysis methods can make a significant contribution to this armoury, but that they should be regarded as only a part of it. We will therefore consider some examples of both pyrolysis and non-pyrolysis approaches, before dealing with the case history in the later section.

2.1. Chromarograpb ur~d mass specmmetric mrthods

2.i.l. Gus chromatography (CC), mass spectromerry (MS}, and CC-MS The development of reliable and efficient autosampling has translated the widely-

used technique of GC into one which can be used with minimum manpower for some routine forensic analyses. For example, excellent reproducibility of blood alcohol determinations, using head-space analyses with an autosampler, can be achieved [I]. Headspace analysis is especially useful when difficult samples such as biological fluids and tissues need to be investigated for volatile toxic compounds. Headspace analysis has also proved useful in the examination of post-explosion debris [2] and in the detection of arson, where it has been used to detect ppm of added fire accelerants in fire debris 131.

Direct MS analysis may be difficult with natural product samples which contain many components, because unless special techniques are used, the overall mass spectrum corresponds to the superimposition of the cracking patterns op all the components present. This problem may be overcome to some extent by the use of ‘soft’ ionisation techniques in mass spectrometry, i.e., mcdes of ionisation in which the ion fragmentation is minimal, and the components are revealed as their molecular ion peaks. Examples of this are the use of Fast Atom Bombardment ms (FAB) and Secondary Ion Mass Spectrometry (SIMS) to authenticate ancient Chinese paper from the characteristic dyes present [4]. These ionisation techniques

R.S. Lehrk/J. Rnal. Appl. Pyro!vsti N-41 (1997) 3-19 5

involve the suspension of the sample in an involatile liquid matrix such as glyarol, and its bombardment by particles with translational energies of thousands of electron volts. (In FAB, :I3e par-ticks may be argon atoms; in SIMS, caesium ions arc: often used).

GC-MS clearly provides the advantage of the separation of the components before mass analysis, and this can lz very useful in pioneering detective work. In some cases, some preliminary chemistry may be advantageous before the GC-MS analysis. An example of this is the detection of drugs in urine, where it is ck.imed that prior hydrolysis and acetylation provides a routine for +& GC-MS cbaracter- isation of more tban 1500 drugs [5J. (The three drugs Cannabis, Cocaine, and LSD, require special sarnplc preparation for this procedure). Since drugs are more concentrated in ulinc than they are in blood or hair, this is a valuabk hitial detection method. However, blood analysis gives more quantitative re&s, and hair analysis can provide evidena of the frequency of drug-taking over a period of several months.

In general terms, it can be said that both PY-GC and PY-MS have both proved valuao;~ 5 providing libraries of pyrolysis patterns which may be used to charactcrise a very wide range of materials, samples of which may be availabk only in microscopic amounts. A typical example of this application is the characterisa- tion of paint Bakes in forensic work. The Metropolitan Police Forensic Science Laborator& in the UK have evaluated thm pyrolysis techniques in considerabk detail [6], and concluded that PY-GC is more valuable for some systems, and PY-MS for others. Their genera1 conclusions for alkyds, acrylics, and vinyl acetate paints are shown in Table 1. An example of the pyrolysis mass spectra of i;;tyd paints, with and without polyurethane modification. is shown in Fig. 1 (taken from

Table 1 Relative suitability of PY-GC and PY-MS in paint chatactctition

Resin type charaaerisation

PY-GC PY-MS

1. Alkyds (a) In general (b) Diffuiag of polyhydric ntcohol mmposition (c) Differing in oil length (d) Modified with stpnc or vinyl toluene (e) Modified with polyurethane tfi Modified with silicones (g] ModXxd with aminorcsins (h) Mc~Iified with nitrmellulose

Good Good Poor Good None NIXI.? POOr None

2. Acrylics Goud

3. Vinyl acetate Good

Gm?4t Poor

Good

Some Poor None

m/z Fig. I. Mass pyrograms of alkyd paints with ;Ind without polyurethane modilkation. The upper pyrogram is B typicul unmodified alkyd, characteriscd by contributions from path& anhydridc (IPI/: 148. 104, 76. NC.) and hydrocarbons (ml-_ 41, 55. etc.). The lower program is a similar alkyd modilkd with a toluene diisocyanate-based polyurethane which contributes the characteristic ion at rttiz 174.

[6]). In pattern comparisons of this kind, multivariate analysis [7] and artificial neural r&works [8] may be applied when the pyrograms or mass spectra are very complex. In some cases, such as the differentiation of genuine Baltic amber from the many forgeties on the market [9], the chromatograms of the pyrolysis products are so different that no such statistical comparisons are necessary.

Up to the present time, forensic studies have not utilised the capacity Df PY-GC to measure rates of pyrolysis rather than products of pyrolysis, and the tempera- ture-dependence of the results is rarely explored. Since studies of this kind can provide very sensitive differentiation between samples of plastics, resins, and rubbers of different origins, there is great potential here for future development. A basic requirement for such work is a pyrolysis unit with precise control of the temperature and duration of pyrolysis [IO].

PY-GC-MS offers the most versatile approach for the study of new systems where basic detective work is needed. Examples will be provided in the case history described in the next main section of this paper.

An excelient general reference book on the forensic applications of mass spec- trometry has been published by CRC Press [I 11, and applications in explosives analysis are reviewed in [II!].

2.1.3. Liquiii clrrtwrarogrqol~y (WLC) md gel-pcrrrreution rhrorfkdograph~ (GPC} Recenl developments in the HPLC technique for forensic use include the

incorporation of multiwavelength UViVisible detection which is used for ‘Ab- sorbance Ratioing’ [13]. This ‘AR’ technique k based on the combined use of retention time and spectroscopic absorbance ratio data. Forensic use has included (a) characterising the dyes present to the extent of about So ng in a single strand of fibre 3 mm long, (b) identification of the supplier of an illegal drug from the dye present in the formulation, (c) detecting the remains of’ an orange biscuit in the stomach contents of a woman who died under suspicious circumstances. (d) characterising the marks left by lipstick and uail varnish. (e) identifying new ball-point ink on an altered document, and (e) identifying wax on the jumper of a suspect with that in a green candle used as a light source in a robbery fl3].

Similar developments of the GPC tehnique have also led to the incorporation of mutidetection systems. Thus, Williams and Langdon [14] use (i) a UV absorbance detector, which has high sensitivity for components which absorb in that region, [ii) dynamic light scattering. which permits the diffusion coefficient of the component to be evaluated, and thence the hydrodynamic radius. (iii) combined refractive index detector plus multiangle laser light scattering+ The latter provides a measure-

Fig. 2. X-ray ridiognphy weals modem n&s inside this supposed 14th Century italian wood sculpture. It is an excellent 20th century crrving made by Donna. who did not intend it as a kvgery. though ir was pascd on as such.

R.S. LeRrle i 1. And. Appi. Pyrolysis 40-41 (l!W7) 3-19

Fig 3. PY-GC of the gray plastic material in the switch. I pg was heated for IO 5 at 15OT The presence of a styrcnc monomer peak (arrowed), was continned from its retention time. This indicate that free monomer is present in the plastic, because no degradation to monomer could possibly have occurred in IO 5 at ISO’C.

ment of the radius of gyration of the molecules, and the ratio of this to the hydrodynamic radius helps to assess the general molecuIar shape. This approach has been used to characterise gum Arabic, a natural polysaccharide produced by the Acacia tree when stressed by heat, drought, or wounding (141.

2.2. UV and IR methods

2.2. I _ Pho togrqAy

Photography of documents with UV illumination is especially useful when all visible traces of ptinting or writing have been removed. Residual components from the ink generally absorb in the WV, and hence appear black in the UV photograph. The UV fluorescence from the residues can also be photographed by using suitable photographic filters. Forged identity q?ocumcnts have often been detected in this way. Intiared photography (using an IR film and an IR filter) is useful in the examination of documents partiaily carbon&d in fires,

2.2.2. Specrroscopy Conventional IR spectroscopy is widely used in forensic work; for example in the

examination of paintings and ancient artifacts [15], and also (in conjunction with PY-GC) to build up an identification library of 179 commercial adhesives [16].

23.1. Optical Comparison optical microscopy has been known for some time as a method of

relating bullets to the gun-barrel down which they have passed, scratches to the

R.S. Lehr&e!‘X Anal. Appt. Pyrolysis 40-41 (1993 3-19 9

tools which caused them, and tibres to the garment or carpet from which they came. Optical microscopy is also extensively used in the biochemical and medical tests in forensic work.

2.32. Electron microscopy Scanning electron microscopy @EM) has opened up new vistas in forensic

detection, as the following examples show. Lay [17] has demonstrated the presence of red blood cells on prehistoric stone impkments 100000 years old by SEM, and Hortola [18] has detected bIood in this way on the asphalt of a pedestrian crtig, despite the intervening sun, wind, rain, pedestrians, and vehicles over a period of 8 months. The same author has also used the method to detect traaz of blood on soft substrates, such as paper handkerchiefs and mummy-cloth. Recently, gold-q&a SEM performed by Ian Freestone at the British Museum has shown that one of the mysterious iock crystal ‘Aztec’ skulls is a modem fake. The evidence lies in the fact that striations on the surface are too regular for human handw:&, and indicate the use of machine tooling. A similar skull in the Smithsonian. Washington, is also a fake.

Fig. 4. PY-CC-MS of the grey ptastic material in the switch. 5 M were heated for 10 s at HOT. The arrowed pt.& in this total ion cuccc~lt cbtomatogram was coohnwxi to be styecoc monomer by recalling the mass spectrum of scan 334 from the MS data system. The s~cctrum obtaiood was simiI;u to that shown in Fig. 5. (The other large peak in the chmmatogtam is tolucne, which wx wed as a s&mt. and should be ignored).

,?. 4. x-ru.v5

2.4. I. X-IU~ specrroscoyy The term X-ray emission analysis covers both electron probe microanalysis and

X-ray Fluorescence analysi! (XRF) !19]. In electron probe microanalysis, the material is scanned by a high energy electron

beam (e.g., as in SEM), which causes X-rays to be emitted from many elements. The wavelength of the X-rays is characteristic of the element, and a plot of the intensity of the X-rays versus wavelength (X-ray emission spectrum) allows the elements to be detected. The method can detect elements close to the surface of an object (depth 1 u) with a sensitivity of 10 - Id g.

In XRF, the material is irradiated by an X-ray beam, giving rise to X-ray fluorescence, which is again characteristic of the element. This technique is less sensitive (1 ppm), but is more quantitative, and has the advantages that it can examine samples at low temperature and at atmospheric pressure. This method demonstrated that a supposed Han Dynasty (BC206-AD220) gilt bronze bear is :L fake, because there is a complete absence of mercury in the gold-plated surface (201. Supporting evidence that it is a forgery came from optical microscopy, which indicated surface blisters characteristic of a modern electroplating process. In addition, X-ray diffraction (the other X-ray spectrometry technique) showed bogus pigments stuck on with a modern adhesive to provide a ‘patina’.

2.4.2, X-ruy rudiugraphy X-mys have frequently shown the presence of surprising under-pictures in oil

paintings [21]. They itlso played a part in exposing the Dossena fakes 1221. Alceo Dossena ws 3 modern Italian craftsman of astonishing talent who created ‘an- tique’ stone and wooden sculptures; for example he created some which were identical in style with carvings from 14th Century Italy. An unscrupulous middle- man passed these off as genuine, and made astronomical profits which were not passed on to Dossena. The sculptures were so good that many museum authorities throughout the world were reluctant to accept that they were not genuine. X-ray radiography such as that shown in Fig. 2. which shows the presence of modem nails in the interior, helped to convince them.

2.5. Isotope nnd tllc~~,raluminescer~t drttitrg

2.51. Radiocarborr dating Radif,active carban “C is continually being created in nature by the interaction

of cosmic rays with atmospheric nitrogen, and it is continually decaying with a half-life of 5730 + 40 years. These competing processes have been occurring for so long that an equilibrium rdtio has been attained of radioactive/nonradioactive carbon, which corresponds to 15.3 k 0.1 disintegrations per minute per gram of total carbon. All living matter incorporates radiocarbon in this ratio, but when it dies, the introduction of new carbon into the specimen ceases, and the 14C starts to decay with the above half-life. The age of the sample (i.e., the period between the

RS. Lhle,‘J. Anal. Appl. Pyrolysis 40-41 (1997) 3-19 Ii

Fig. 5. Mass spec~rutn of a chromatogtaphic peak (scan 365) in a total ion cumt chromatogram of the oily contamination from within the switch. This shows that the chromatographic paL corresponds to styrene monomer.

death and the present time) can therefore be calculated from the simple first-order decay equation. Corrections must be made if there is spurious radiation present (e.g. natural radon). The accuracy of the method has been confirmed by the dating of historical samples of known age.

In recent times, the sensitivity of the mahod has been incre& by a factor of 100 by use of the ‘Accelerator Mass Spectrometric (AMS)’ method, which has been developed at the uniwrsities of Oxford, Zurich, and Tucson (Arizona). Instead of measuring the rate of decay of the “C present by use of a scintillation counter, the total number of such atoms in the sample is counted by mass-resolving this isotope in a mass spectrometer. Milligram sampies are sticient for AMS dating, and samples of this size were taken from the Turin shroud and asses& in I989 1231. The results indicated that the material was made in 1260-1390 AD, so regrettably it must be concluded that the relic is a 600 year-old fake.

25.2. Chlorine daling When the surface of a freshly-cut rock is exposed, cosmic rays strike it and begin

to build up in it concentrations of the isotope WI. The amount of this material in the rock therefore provides a measure of the time that has elapsed since it was mined or exposed by natural processes. This approach has been used recently [24]

12 R.S. Ldrle/J. And. A~ppl. Pp$m 40-41 (i997) 3-19

to test a theory that the smaller dolerite bluestones in Stonehenge were not transported by human effort on sea and land, but were carried on a huge icesheet during an ice-age. The chlorine dating showed that the bluestones date from about 14000 years ago. Since, as noted by the author [24], the last glaciation in that area was 400000 years ago, it seems that human effort was involved!

25.3. Tharmaluminescent (TL) dating This method can be used to date pottery, terracotta, and general ceramics.

Thermoluminescence is the light emitted when ceramic material is heated to approximately ltNM°C. The light arises from the release of energy which has been stored as a result of electrons trapped in the imperfections in the lattice of the quartz in the ceramic, The stored energy is provided by the absorption of nuclear radiation from uranium present in the pottery clay. The TL intensity is proportional to the total dose of radiation received. Dating is possible because heating the object to 500°C removes the TL. Thus when the pottery is originally made and tired, its stored energy is reduced to zero. Its TL then grows with time, and measurement of its present TL allows the age to be calculated. (The procedure involves calibration with an artificial radioisotope, and is rather complicated). A recent application of the technique (25) showed that what was believed to be a valuable Eauscan terracotta figure of 500 BC is no more than 56 years old.

2.6. Biaclrenrical tnethods

Biochemical methods, which include DNA fingerprinting (developed at the University of Leicester) ]26], and Fluorescence Polarisation Immune Assay (FPIA), are now of fundamental importance in forensic work, but are outside the scope of the present paper. Suffice it to be said that precise estimations by the latter method go to the femtomolar (lO_“) level, which means that a urine sample can reveal a single cannabis joint smoked several weeks previously.

2.7. Stylr/partem rrnaiysis

2.7.1. Style analysis The initial indications of fakes in the art world usually come from a person

whose vast experience of artistic styles tells them that there is ‘something wrong’. The human brain is superb at instinctive pattern recognition, and it is only recently that computer programmes have been devised which are able to decide that a given painting is probably by one artist rather than another. (A sinister corollary of this is that such programmes can be used to generate ‘authentic’ paintings, or to convert a photograph to one. A newspaper recently ihustrated this by providing us with a ‘Renoir’ and other versions of Princess Diana). The characterisation of handwriting style is more tractable, and computer detection of handwritten forgeries can now be more rciiable than human judgment.

2.7.2. Pattern analysis In 1913, fingerprint anaIysis helped to convict Vincenzo P~nsgia, the man who

one year earlier had walked out of the Louvre with the Mcna Lisa. At about this time, a photograph of the USA central police fingerprint room shows scores of people at desks making the visual comparisons. Today’s computer&d systems allow comparisons to be made at a rate greater than 6OooO s- *.

Those who operate mtiem mass spectrometers will be aware that the data handling system on the relatively modest computer has software which can compare a chosen mass spectrometric scan with tens of thousands of Ii- mass spectra in a few seconds, (Operators will also he aware that one should he cautious about assuming that the best fit necessan ‘ly identifies the component! This caveat is quite important if there are forensic implications.)

Another example of recognition which may well bzome important in stcurity systems of the future is the pattern of the eye iris. It is claimed that this is unique to I in 10”, and could become the most convenient tag for every human being.

A final comment under this heading is to remind the reader of what was said in Section 2.1.2. about the utilization of multivariate analysis and art&id neural networks in categorising complex patterns of data.

2.8. Other mezhodr

Of the many other methods which are b&g applied, mention must at the very least he made of neutron activation analysis and of atomic absorption spectrometry. For the general principles underlying these, and indeed of the broad picture of forensic science, the reader is referred to the monograph by Broad [271 and the book by Kaye [28]. Excellent general refcrtnces on forgeries in zut and archeology are the book published by the British Museum [23], the review by eddy [20], and the work by Fleming [29].

3.Acasehistmy

3. I. Investigation of the curse of switchgear fuilure

3+1.1. introduction Several years ago, a firm which supplied reliable heavy-duty electrical switches

received complaints that some of the switches in a new batch were displaying preliminary indications of failure. One such switch did indeed fail, and during melt down it could have provided a potential Cre risk.

The components in the switches were as follows: (i) The metal contacts. (There had recently heen a change from Ag plating to Ni

plating). (ii) Grey moulded plastic components. (There had recently &II a change from

phenol- formaldehyde resin to a polyester-styrene modding compound). (iii) Black moulded components (Nylon46 compound)

14 R.S. Ldwle/J. And. Appl. Pyrutyw 40-41 (1997) 3- I9

(iv) Colourless sheet insulators (Polycarbooate) (v) Switch lubricant (Recently changed from Hydrocarbon grease to Silicone

grease).

3.1.2. PY-CC and PT-E-MS studies oJ the components in u new switch

3.1.2.1. Thr nylon. Temperature sequence pyrograms were recorded at IOO”C intervals. At 13O”C, the desorption of expected contaminants (surface lubricants, antioxidant, etc) was observed. At 230°C no decomposition was detected, and significant decomposition was not observed until 430°C. On this basis, the behaviour of the nylon did not appear to be abnormal.

3,f,2,2, 7%e polyc&u~ote. Some expected contaminants were desorbed at 130°C, but again, the behaviour of the polycarbonate did not appear to be abnormal, and was quite consisteilt with the characteristics of polycarbonate which had previously then found to be reliable. Furthermore, the polycarbonate was not sited near the switching region. It was therefore considered to be an unlikely contributor to the switch failure.

3.1.2.3. T/K grey plastic. The behaviour of this material did seem to be unusual, PY-GC of I J_Q at 150% showed that the material must contain free styrene monomer, as shown in Fig. 3, in which the styrene peak was characterised from its retention time. This was confirmed by PY-K-MS (Fig. 4), which showed that free styrene monomer is present, and is readily evolved at 13O*C.

On the basis of these experiments, it was proposed that the niost unexpected aspect of the materials in the new switch was the presence of considerable amounts of free styrene monomer in the grey plastic material.

3.1.3. Investigation of a switch run IO ‘imminenr @lure’ In an attempt to simulate switch failure conditions in a controlled laboratory

environment, a bank of three switches was overrun continuousl} at 85 amps, i.e., 10 amps above the specification rating, until the interior switch temperature attained 10S°C, which is about 2O’C above the normzi operating temperature.

The switches were then dismantled, and examined in the following way: (a) The interior compartment: this was found to be almost completely covered

with a viscous liquid. When this was subjected to GC-MS analysis, it was found that it consisted IargeIy of styrene monomer (Fig. 5) and phthalates (Fig. 6), the latter almost cenainly arising from the release of plasticiser from the grey plastic,

(b) The wipers and contacts: these metallic components were found to be contaminated by traces of a white solid at the contact points, as shown in Fig. 7. These contact areas were scraped with a scalpel, and the metal and powder scrapings were transferred in to a meltingpoint tube. Methylene chloride (2 mg) was added to this tube by means of a syringe, and the tube was warmed. Then 1 JAI of this solution was then deposited on the filament, the latter inserted into the PY-GC chamber, and rhe filament heated at t50°C to drive off the solvent and any

R.S. Lelde/J. Ad. Appl. Ppl,sis 40-4 (1997) 3-19 I5

volatiles. PY-GC-MS was then performed at a pyrolysis temperature of 400°C for 10 s. A mass chromatogram of m/z = 104 (Fig. 8) indicated that the chromatographic peak at sczx 370 corresponded to styrene monomer from the pyrolysis of polystyrene, and this was confirmed by its mass spectrum (Fig. 9). These results lead to the surprising conclusion that polystyrene is the principal component of the white material collected from the switch contacts.

3.1.4. The proposed sequence of events kadhg to switch fuilure On the basis of all of the evidence obtained, it was proposed that the tollowing

sequence of events was responsible for the switch failure: (i) The new switch lubricant showed a greater tendency to creep into the actual

contact area than the original, and caused some increase in contact resistance. As a result, the switch contacts heated up slightly, and warmed the switch unit, though probably to no more than NW’C.

(ii) As a result of (i), the grey moulding released both phthalate plastickr and free monomeric styrene, which further covered the contacts and caused additional heating. This cycle then proceeded, releasing more styrene monomer.

(iii) The freshly generated nickel surface on the wiped parts of the contacts induced polymerization of the styrene mcmomtr in the region of the contacts. This then caused a large increase in contact resistance, causing an escalation of the temperature.

fig. 6. Mass spectrum of scan 1122 in the total ion currem chromatagram of the oily cantaminarion suggests that the chromatographic peak at that ~gn number (the largest peak in the chromatogram) corresponds to a phthalate plasttisr, possibly diethyl phthalate.

16

Fig. 7. Examination nv L switch before imminent failure. This photograph shows both parts of the nickel-plated wiping components taken from the middle switch of the bank of three. [The Cl-shaped wiper. in the upper pan- of the figure. has been bent out to horizontal in order to photograph it). The regions indicated by arrows were observed tu be very lightly coated with a whitish residue. The metal surface here was scratched away in or& to remove this deposit for analyses. No similar deposits were observed on any other parts of these metallic wipers.

(iv) If the switch is still left in circuit, the large increase in temperature causes melting of the plastic components, especially of the nylon, leading to structural collapse of the inner part of the switch. This results in a short circuit, which can ignite the vapour (rich in styrene) within the switch.

It was almost unbelievable bad luck that all three changes in the materials introduced by the manufacturers should have played a part in causing failure. The new lubricant, the new polystyrene/polyester component, and the replacement of the silver plating by nickel, each contributed in its own way towards overheating. When this was realised, the manufacturers chose a more suitable plastic, a more appropriate lubricant. and reverted to silver-plating the contacts. Since that timt there has been no report of any failure.

4. Postscript

In this paper, an attempt has been made to show how pyrolysis methods fit into the overall armoury of techniques which may be applied to the study of forensics, fakes, and failures.

RX Lehrle /J. Anul. Appl. Pyral# 40-41 (1997) 3-19 17

The scientist has spri~l respsihi!i+s in these xcas, because unreliable work can lead to the loss of freedom or reputation for others. Public pressure on the Police to pull in suspects and obtain convictions can be very great, and this can lead to the temptation to miaimise the uncertainty in the scientific results in Forensic work. And as some recent examples in the CiK have demonstrated, once an innocent person is convicted, it may take many years to secure their release.

It is not always easy to strike the right balance between securing convictions and retaining personal freedom. What degree of suspicion merits the typing of a telephone? A security video will helpfully record intruders, but is it acceptable that it is also continually monitoring the workforce? Obtaining fingerprints or body fluids from volunteers is acceptable to everyone, but what degree of suspicion is required for them to be taken by force? When does a person used as a decoy, who is used to secure a convirtion, become an agent provocnteur? There are no simple and universal answers to such questions, but they cannot be ignored.

Ackmwkdgenmts

The author expresses his gratitude to Dr Paul Gardner, Dr James Riches, and Dr Robert Williams, who cooperated in solving the switchgear problem during the

Fig. 8. Mass chromatogram aT the ion of nriz = 104 in (i.e.. dK contributioo ol this ion to) the total ion chromatogram of the pyrolysis products frwm the white deposit on the switch contacts. This indicates that the chromatographic peak in the same poisition (szm 370) in the total ion chromatogmm probably corresponds to styrene.

18

Fig. Y. Mass spectrum of scan 370 in the total ion current chromatogrdm of the pyrolysis products from the white deposit on the switch contacts. This closely rrtimbles the mass spectrum of styrene monomer. This leads IO the surprising conclusion that polystyrene is the principal component of the material extracted from the metallic switch contacts.

time when they were postgraduate students in the Polymer Group at the University of Birmingham. Thanks are also due to Dr Cohn Graham, a colleague at the University of Birmingham, for some helpful comments on the original manuscript. Acknowledgement is also made of the many articles and books, too numerous to mention, which have provided background to the investigative methods described. The author will be pleased to hear sf any new methods or updates which are relevant to the topics covered in this paper.

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