CORRESPONDENCE

Exhaustion of ethanol simulator solutions Sir: I have been involved in several cases where the Calibration test solutions for Evidential Breath Analysers have been left in service for more than the recommended 35 procedures. As a result the defence has argued that the test readings were invalid. It was decided that a short experiment would help to uncover the number of procedures that could be carried out using one solution before the ethanol content of the solution fell to such a level that it was no longer giving an ethanollair mix of 32 micrograms (pg) or over. Mr Tony Mather of Camic kindly helped by supplying an unopened BDH - Ethanol Solution and with the use of pumps and flow metres.

0 25 50 75 100 125 air passed through solution (L)

The ethanol solution was placed in a standard Carnic cell and allowed to warm up to 34.0 "C. The temperature was monitored throughout the experiment and found not to fall outside the range 34.0-34.1 "C at any time. Once at operating temperature, two specimen 'breaths' were blown through the cell into our Camic Datamaster using a standard baffled mouth piece. The ethanol level was recorded to one decimal place. Each specimen 'breath' was found to average a two litre volume through the solution.

After the test blows, the cell was connected to a pump of 275 Lhour flow rate for one minute and 4.58 L of air bubbled through. The test blows and the one minute bubbling of air were repeated until the ethanouair mix of the cell had fallen to 31 yg, 1 pg below the lower calibration level of 32 pg. The test results are shown graphically (Figure 1) together with the calibration results from the Gas Cylinder supply on the Datamaster. The average of each of the paired results are shown. As can be seen, the cylinder standard remained fairly constant throughout.

Tests upon a standard Camic pump showed that a flow rate of 130 Lhour into a Camic Breath Analyser for 15 seconds was the maximum normal requirement for each calibration test. This was equivalent to 0.54 L per test or 1.08 L per complete procedure. Lion laboratories informed us that the Lion Intoximeter 3000 draws a maximum of 800 mL per simulator activation which is equivalent to 1.6 L per complete procedure.

FIGURE 1 Graph showing drop in alcohol concentration with passage of air through simulator cell.

Solution 0 Gas Standard --

It was concluded that the reliability of a simulator solution should not scientifically be called into question until it had been used for considerably more than the recommended 35 procedures. Also, given the fluctuation in calibration tests usually observed with the first generation Evidential Breath Test devices, it is considered probable that the calibration test may well fail to reach calibration, and therefore abort, before the solution itself is exhausted.

It is further suggested that in cases where 'over use' of a simulator has occurred, analysis of the average calibration results for procedures using the questioned cell should show a similar gradual fall in values. If such a fall is seen the device would most probably be detecting ethanol at the correct sensitivity. If a fall or even a rise were observed, the test results could be corrected accordingly.

Only in cases where breath alcohol levels of close to 40 pg are recorded and a simulator has been in use for 50 or more procedures is there likely to be the need for correction or concern.

December 1995 Andrew Stephens Formedecon Ltd Mountjoy Research Centre Durham DHI 3UR

Our results indicated that approximately 90 L of air could Interpreting Evidence be passed through the simulator solution before the

Sir: As one of the former editors of the Society's Journal I simulator reached an ethanollair mix of 32 pg. This equated

recognise the unusual step I'm taking in corresponding to approximately 83 complete procedures on the Camic and

about a book review [I]. The book in question is 56 complete procedures on the Lion machines.

'Interpreting evidence - evaluating forensic science in the Given that the simulator solution is manufactured under courtroom' by Bernard Robertson and Tony Vignaux. very stringent quality control (Ethanol content of 89.3 mg Having now read the book twice and the review thrice, I am + 1 mg per 100 mL - source BDH), it was assumed that the left wondering if the reviewer (Stuart Kind) and I have read variation between solutions would not be large enough to the same book! Three main gripes prompted me to protest warrant repeating the experiment. about the review.

Science & Justice 1996; 36(2): 129-130 129

Correspondence

First, its effect may be to put off people who might benefit from reading the book. I tend to take book reviews seriously: if someone whose judgement I respect intimates that a book has serious shortcomings, then I may well pass up reading it in favour of something else. This would probably have been my reaction to the review of 'Interpreting evidence' had I not just finished reading the book.

Second, the reviewer spends the first 50% of his discourse nitpicking and in the process misses the point of the book, which is to encourage people to think differently about forensic science. I found the style of the book readable and encouraging; the style of the review in places is disdainful, if not downright pompous. There is one crumb of encouragement. Although it is 'impossible to recommend it to any professional who is directly concerned with the criminal investigation and trial' the book is 'written with a refreshing enthusiasm which ... demands even the sceptical reader's attention'.

ERRATUM

We apologise for an error which occurred in Volume 36, number 1, page 3 1. The caption for Figure 3 should read as follows:

FIGURE 3 The two images compared are between a black and white security camera still photograph of the robber with a photograph of the suspect. A horizontal wipe is employed to show the shape of the ear of the robber compared with that of the suspect in figures (a) and (b). Similar wipes are employed to show the characteristic shape of the right eyebrow between suspect and robber.

Finally, we are told that the book should be re-written 'this time not in a hurry ... with text subject to critical scrutiny by a group of readers who are professionally and practically concerned with the problems the book purports to treat'. Well, excuse me, but I can't see how the book could possibly have been written in its present form without recourse to such people!

This letter is not intended to be a second review. Its purpose is to persuade those who may have been put off by the Science & Justice review from reading 'Interpreting evidence' to think again. Suffice it to say that I recommend the book to my colleagues and would make it required reading for any prospective court-going forensic scientist.

[I] Kind SS. Hamlet without the Prince. Science & Justice 1996; 36: 65-67

March 1995 Roger Davis Metropolitan Police Forensic Science Laboratory London SE1 7LP

Science & Justice 1996; 36(2): 129-13d