Expert Witness (11 page)

I
received a call from a solicitor one day and after the opening pleasantries were over he said, ‘I have a client who's been charged with drink driving. She was stopped by the police after she drove out of the airport when she'd just returned from a trip to the States to get breast implants.' And that's all he said. I was waiting for him to add some details about what she might have slugged from her duty free while she was waiting the usual interminable time at passport control but no, nothing else was offered. So I said, ‘And what happened next?' to which he replied, ‘Nothing. That's it.'

Her whole defence to drink driving was that she'd had new boobs in the USA and they were the reason for her being over the drink-drive limit. Now, to every woman (and, in some circumstances, men) out there with new boobs, this is not a defence to drink driving. The breath reading was over the legal limit not because her new boobs were filled with brandy but because she'd got sloshed on the free booze in business class. No defence.

Same goes for pickled onions. Eating five pickled onions from the jar on the counter in the chippy will not put you over the drink-drive limit; it'll be the 10 pints of lager you had in
the pub before you had a punch-up and a kebab on the way back to the car.

 

So far, I've not really talked much about how forensic science is applied once the theory's been learnt, so here we go. I'm going to start with a personal favourite of mine, alcohol. Before we all get confused, this is not a break down of my drinking habits — I am the mother of two relatively young children and I run a small business; there is no time for relaxation unless it involves 10 minutes of crime novel reading followed by sleep.

This chapter is more about how alcohol crops up in casework, how we deal with it as forensic scientists and what it all means. After all, alcohol is a hugely popular drug. The ancient Egyptians were kind enough to leave behind pictographs showing the use of wine around 6000 years ago. There is also suggestion that Neolithic people were fermenting alcohol and had stone beer jugs, which would put the use of alcohol as far back as 9000 years ago, during the time period to which geologists and archaeologists refer as the Holocene.

Most parents worry that the ‘youth of today' are starting to drink alcohol younger and younger, and they should be very worried. A 1997 study involving data from more than 27,500 current and former drinkers in the USA showed that 40 per cent of adults who started drinking at or before the age of 14 developed a lifetime dependence, compared with only 10 per cent if they start drinking at 20 or older. Unfortunately, alcohol is so socially acceptable that it's a major contributor in a significant proportion of crimes, often drink driving or those crimes to which we refer as ‘crimes against the person' — some times they're one and the same. In New Zealand, as
I under stand it, alcohol is a factor in a quarter of all traffic offences, a third of violence (including domestic) cases and half of all serious violence cases. You just have to take a look down your local high street on a Saturday night to see what I mean — it's everywhere and, dare I say it, New Zealand is a hard-drinking nation.

We are, as a society, extremely reliant on our motor vehicles; the idea of not being able to drive for nine months, 12 months, or even longer, is more than we can bear. Some people will lose their jobs and, potentially, their homes if they lose their driving licence. For this reason, many people choose to defend a charge of drink driving but the question of defending oneself is occasionally asked. My favourite answer comes from an Auckland-based barrister who reassures potential clients that, yes, you can indeed be convicted, sentenced and jailed completely free of charge. If you want help navigating the technicalities that are a drink-drive defence, perhaps legal advice should be sought.

In forensic casework, we look at how alcohol may have influenced a sequence of events that leads to the eventual ‘event of interest'. It could be some thing as relatively insignificant as someone moving their car 10 metres down the road after they've had a few drinks and clipping next door's Ford Fiesta while they're parallel parking, or it could be some thing far more extreme, such as a drug and alcohol-fuelled frenzy, which results in someone being kicked to death.

In all cases we have to consider several things, including the pattern of alcohol consumption (such as what was drunk and at what times), what time the crime/incident occurred, the drinker's vital statistics (height, weight, gender — age can
also be taken into consideration), any medication, what the driver might have eaten and how used they were to drinking alcohol. We undertake several sets of calculations to work out the blood alcohol concentration people achieve after drinking. At the time of writing, New Zealand law stipulates the drink-driving limit as being 400 micrograms of alcohol per litre of breath or 80 milligrams of alcohol per 100 millilitres of blood, although there are rumblings about lowering the limit to 50 in blood (and a corresponding reduction in the breath limit).

If you're under 20 years old, the figures are 150 micrograms of alcohol per litre of breath and 30 milligrams of alcohol per litre of blood. These numbers relate to how much alcohol is travelling around in the blood at the time the needle enters a vein for a sample to be taken, or how much alcohol is in the breath when someone breathes into one of those nice pieces of testing kit at the police station. In England and Wales, providing a urine sample is also an option but it can complicate matters from the calculation perspective because of all sorts of issues around how long since the person last had a wee, whether the sample was collected in accordance with certain procedures, and so on.

The blood/breath (and urine) alcohol calculations follow the original work of a Swedish scientist, Erik Widmark, whose seminal work was published in the 1930s and then translated into English. Much work has been done since then in order to refine the accuracy of the calculations, and a lot of that additional work has used data from actual drivers and casework, as well as data from study groups.

The most common calculation converts the alcohol in the glass into alcohol in the body. By this I mean it converts
the alcohol in, say, a bottle of beer into a blood alcohol concentration for a particular person. For example, a stubbie of Mac's Gold contains 330 millilitres (ml) of alcoholic beverage of which the alcohol makes up four per cent of the volume. This is what ‘4% ABV' (or ‘alcohol by volume') means on the side of the bottle. Four per cent of 330 ml is 13.2 ml so 13.2 ml of the total volume is made up of alcohol. When this is converted to actual grams of alcohol, this is 10.43 grams. So there are 10.43 grams of alcohol in an average bottle of Mac's Gold (give or take the variation allowed during the brewing process, but that's a different story). If my brother drank that Mac's Gold, it would contribute about 14 milligrams of alcohol to every 100 millilitres of his blood. If I drank it, it would contribute about 25 milligrams of alcohol per 100 millilitres of my blood. The difference is because he is male, 6 foot four and about 18 stone (114 kilograms, unless he's been on a diet recently) whereas I am female, 5 foot 8 and about 9
¹
/
²
stone (60 kilograms).

You can easily see that if we drank several of these each, I would be over the blood alcohol limit for driving far quicker than him and it would also take longer for me to drop below the legal limit again because I would have a higher concentration of alcohol in my blood — I'm smaller by volume, I therefore have less space into which to distribute the same volume of alcohol, ergo my blood alcohol concentration will be greater. When it comes to alcohol concentration, the human body is like a big bag of water. If you pour a cup of blue dye into a small bag of water, the dye will be more concentrated than if the same volume of dye is poured into a big bag of water — it's the same principle with people.

There are two separate processes to consider when talking about the fate of alcohol in the body (that is, what happens to it when it's inside you): absorption and elimination. Absorption is all about how the alcohol is soaked into the blood; elimination is about how the body gets rid of the alcohol once it's been soaked up. People often get these two processes mixed up but they're separate, even though the time they occur overlaps.

Absorption
is what happens to the alcohol once it is poured into the mouth and flows on into the gastric region — the stomach and small intestine. For the years I worked in England, alcohol cases were always considered without much regard for whether or not someone had been drinking on an empty stomach, but it does make a difference and there's now plenty of scientific literature to support that view.

What seems to be at issue is what sort of food has the greatest effect on absorption of the alcohol. It's not rocket science — anyone who drinks even occasionally will know that whether or not they drink on an empty stomach will affect how they feel after they've had a few drinks. This is because alcohol is absorbed more quickly from the small intestine than it is from the stomach. When alcohol is poured down the throat, the first place it can rest for a period of time is the stomach. If someone is eating or has eaten before they start drinking alcohol, the valve at the end of the stomach (the pyloric sphincter) shuts. Imagine it a bit like a little door that closes when there's food in the stomach. Closing the door keeps the alcohol in the stomach. The role of the stomach is to contain the food and break it down into a mushy paste using various chemicals and enzymes. If there is no food in the stomach, the door at the far end is open, the alcohol can
pour into the stomach and then out again through the door and into the small intestine. Alcohol is more readily absorbed from the small intestine than from the stomach, which means the effects can be felt more quickly.

Most people are aware of this — I'm sure I'm not alone when I say I've heard
many
stories of people getting drunk and, generally speaking, they became drunk more quickly and felt more drunk when they drank on an empty stomach. There's the old wife's tale of lining your stomach with milk before you drink — I assume this works because it causes the pyloric sphincter ‘door' to close, thus containing the alcohol to the stomach and therefore slowing down absorption.

Scientific opinion is that there is an optimal strength and bubbliness of alcoholic beverage that maximises absorption. This is equivalent to a standard gin and tonic. Having said that, what is standard? A standard measure of spirit in England and Wales is 25 ml, in New Zealand it's 35 ml. In England and Wales if you ask for a G and T you'll get 25 ml of gin plus some tonic; in New Zealand you'll get 70 ml of gin plus some tonic because double measures are poured as standard but in England and Wales you get a single measure. Awareness of variation is the key to safe drinking when you're overseas.

Elimination
of alcohol is how the body gets rid of it by metabolising it (breaking it down), largely in the liver. The rate of elimination varies across the general population but is largely independent of height, weight and gender. Once alcohol has been absorbed, it moves around the body in the bloodstream and when it encounters the liver, it starts being removed through the process of metabolism. The process of elimination starts within a few minutes of someone starting
to drink alcohol and the rate at which it is eliminated is pretty constant until the blood alcohol levels get quite low, after which it tails off.

How alcohol makes a person feel is a different matter. Although the amount of alcohol in the blood is directly related to how much alcohol someone has consumed, how drunk someone gets, feels and appears is some times unpredictable, especially when other drugs are involved. However, it's accepted that after alcohol consumption and absorption, people follow a general trend in behaviour and these trends can be related to blood alcohol concentrations. After the first drink, and assuming it's a standard drink and not a yard of ale, many people won't really notice any effect and outwardly they appear just fine. This is the stage when, legally (in New Zealand and the United Kingdom anyway) people are still allowed to drive, with their blood alcohol concentration generally between 10 and 50; several countries in central and eastern Europe have a zero tolerance rule, whereby alcohol consumption means no driving. It has the immediate virtue of being really easy to under stand and implement.

After the stage of ‘no real effects' or ‘sub clinical', behaviour tends to range into mild euphoria, sociability and talkativeness followed by increased confidence, decreased inhibitions accompanied by reduced attention and judgement with some sensory and motor skill impairment and a reduced rate of information processing. Once your blood alcohol level is causing the latter sorts of effects, you definitely shouldn't be driving, from either a legal perspective or a practical one. This is the ‘euphoria' stage (blood alcohol concentration between 30 and 120, legal limit currently being 80). The blood alcohol
limit for driving straddles the sub clinical and euphoria stages.

The ‘excitement' stage is characterised by impaired balance, a reduction in coordination leading to staggering or erratic gait, possible nausea, poor sensory perception, drowsiness and an increase in the time it takes to react to an external stimulus. This and the euphoria stage, in my professional experience, are the stages at which most drunk drivers are likely to think that driving is still a good idea. Blood alcohol levels of between about 90 and 250 occur during this stage.

The ‘confusion' stage (blood alcohol levels between about 180 and 300) involves dizziness, ‘drunkenness' as we know it and disorientation — when you're having trouble getting the key in the front door. Apathy, increased drowsiness and lethargy are also common — so you're likely to pass out when you hit a horizontal surface, whether it be the pavement or your bed. You also might experience an increased pain threshold so you don't notice when you bang your head on the curbstone, and vision disturbances.