Senior Forensic Science Consultant Dr Anna Sandiford, founder of The Forensic Group, discusses breath versus blood alcohol testing in drink-driving cases.
Alcohol: The Evidence Type that Keeps on Giving
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This article is a brief summary of a seminar I gave earlier this year on alcohol, drink driving and breath/blood alcohol results. Bear in mind though that blood alcohol calculations can be undertaken in any case where alcohol has been consumed including rape, sexual assault, domestic violence – they are not restricted to drink driving cases.
As an expert witness experienced across all types of casework, the past two decades have shown me that drink driving cases are amongst the most complicated, inventive and interesting.
- Drink drive cases are complicated because they involve human bodies and how they process alcohol – establishing accurate timelines is critical. People are as different and varied as their accounts of alcohol consumption so in order to undertake calculations, forensic alcohol experts have had to develop averages based on casework samples and laboratory testing. Standard approaches for alcohol casework mean that in any given case, there could be a range of results and the longer the time period involved, the greater the spread of those results. Alcohol is one of the only drugs in the world for which there are prescribed levels for driving. This is because alcohol behaves in a reasonably predictable way in the body, allowing of course for those general ranges to which I referred earlier. How a person feels and his or her blood alcohol concentration are related but, again, in general terms only. A naive drinker will generally feel the effects more than a seasoned drinker but it will also affect how the same person feels on different days – think how a champagne buck’s fizz at a midday wedding reception feels different from a few cans of beer in front of the telly on a Saturday night.
- Drink drive cases are often inventive because people do not want to lose their driving licences. I’ve seen everything from drinking bottles of Listerine after driving to the suggestion that eating pickled eggs adversely affected a breath test result. Generally, you have to put into the body sufficient alcohol to get out a given breath or blood alcohol reading; pickled eggs won’t do it but Listerine might, although that leads onto a credibility argument, which is a whole other kettle of fish (or bottle of mouthwash).
- Drink drive cases are also interesting because people do all sorts of things when they’ve been drinking: I’ll never forget the stealing of a back-hoe loader that got abandoned in the middle of a rural roundabout and the trail of empty lager cans that the Police followed across a field to find the absconded driver. None of that has any relevance to the alcohol calculations but it does mean I have learnt that anything is possible. As a result of the thousands of cases in which I have been involved, there isn’t much I haven’t heard or considered by way of explanation for an elevated blood, breath or urine alcohol concentration although New Zealand doesn’t have urine as a sampling option.
As an expert witness, to undertake drink drive cases involves understanding:
- the basics of how the human body deals with alcohol;
- the differences between absorption (which takes place in the stomach/intestine and takes a variable amount of time depending on food, the alcohol being drunk and other factors) and elimination (largely in the liver within a scientifically established range);
- how blood and breath alcohol concentrations are related and then converting between the two, given that NZ uses different blood and breath alcohol concentration units from other countries;
- what calculations can be undertaken in a given case (forward calculation = estimating a person’s blood alcohol concentration at a future point in time after he/she started drinking; back calculation = estimating a person’s blood alcohol concentration at a point in time prior to when he or she provided a breath or blood sample; total alcohol consumed = assessment of a person’s total pattern of drinking over a given period of time taking into account breath and blood alcohol results if they are available);
- how the various breath testing devices work, what can adversely affect their function and how the New Zealand system operates in relation to how science and drink driving law operate in other countries;
- how blood samples are analysed, what differences in results mean, the difference between hospital results and Land Transport Act sample results and how results can be affected by coagulation or small sample sizes (e.g. second sample containing insufficient blood for analysis);
- only to deal with the information provided. It is for the court to decide what is credible.
In simple terms, breath is easier to collect than blood but blood is scientifically more accurate.
Depending on case circumstances, breath tests can be affected by products such as asthma inhalers, nitrolingual sprays as well as the time the last consumption of alcohol occurred. The printout from the evidential breath testing device (EBTD) should mark up any issues relating to interfering substances and breath differences that occur during the evidential breath testing process. The EBTDs are also set up to receive two samples of breath as standard; receipt of one breath sample is not scientifically reliable even though apparently a single result is regularly offered in NZ courts as a reliable indicator of a person’s breath alcohol concentration at the time of the evidential breath test. New Zealand does not always seem to follow other countries in how EBTDs should be operated and produce results so there are questions raised in casework here that are not seen overseas.
Blood alcohol testing should be specific to the alcohol in alcoholic drinks (ethanol) so asthma inhalers and the like should not adversely affect those results. Samples are collected in hospital-style tubes and the tubes contain chemicals that should stabilise the alcohol content of the sample and prevent coagulation. Samples can be sent for independent testing as long as the second sample is suitable for testing.
Drink driving myths are still prevalent despite New Zealand’s rigid approach to drink driving results although many have no real credibility:
- holding a coin in the mouth when providing breath samples will not bring down the breath result (and let’s think about where coins have been – probably carrying a host of germs and diseases so I wouldn’t recommend sucking them);
- taking antibiotics will not increase the blood alcohol concentration although it may reduce the effectiveness of the antibiotics;
- chewing gum, sweets and eating MacDonald’s will not adversely affect breath and blood alcohol concentrations.
There are ways to affect a breath test, but I’m not going to give those away.
New Zealand has a somewhat unique way of approaching drink driving cases. Some cases have merit although not all, but if you don’t ask, you don’t find out so if there are any potential issues with a case, they are always worth asking. Your client may or may not get the answer they require but there is always something new to learn.
Dr Anna Sandiford is the Director of The Forensic Group Limited, which has offices in Christchurch and Auckland and a network of experts nationally and internationally. Dr Sandiford started her forensic science career in 1998. Her expert witness history includes expertise in alcohol toxicology (particularly alcohol calculations), drug driving, drugs, footwear, glass, physical fits and pollen. Since starting the company, Dr Sandiford has developed expertise in managing large and complex cases, having been involved in multiple high-profile cases including the 2009 Bain retrial, the 2015 Lundy retrial, the 2015 Privy Council decision of an unsafe conviction of Teina Pora for the murder of Susan Burdett and many others. She has been referred to as ‘the expert on experts’ and is author of Forensic Science and the Law: a guide for police, lawyers and expert witnesses (Thomson Reuters, 2013), a second edition of which is in preparation, and the general interest book Expert Witness (HarperCollins, 2011).
Dr Sandiford has worked extensively with Legal Aid and the NZ Law Commission on issues relating to expert witnesses and forensic standards. She is a Trustee of the New Zealand Public Interest Project which is a charity that undertakes case reviews of potential miscarriages of justice. Contact Dr Sandiford at sandiford@theforensicgroup.co.nz
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