Frequently Asked Questions – The Science of Breath Analysis

• If I have a gastric band fitted to control my weight/diet problem, will this affect my alcohol level after drinking? Will it reduce the amount of alcohol I can consume before reaching the legal breath or blood alcohol limit for driving?
  • NO: Gastric bands are fitted to persons with a weight problem, caused largely by over-eating. During surgery the device is placed around the top of the patient’s stomach, and is intended both to reduce food intake and to increase the time taken for gastric emptying. However, alcoholic drinks, obviously being fluids, will pass more easily than solid food through the band, and so escape its intended effect. This means that the use of such a device could not have any conceivable effect on the level of alcohol reached in the wearer’s breath or blood after drinking alcoholic beverages.
• I know I have to wait twenty minutes after the subject’s last drink before running a breath test, to allow for any residual MOUTH ALCHOL to be eliminated; but can I accelerate this process by giving him or her some water to rinse their mouth out with?
  • NO! This can result in a wrongfully low breath alcohol reading. This is because it will line the mouth with alcohol-free water [instead of the saliva, which has previously equilibrated alcohol-wise with the blood], as well as causing a lowering of the mouth temperature. Each of these factors will result in a loss of alcohol from the breath as the specimen is delivered by the subject to the instrument.It is also possible [as has happened] that the subject may later claim that the water they were given had been laced by the tester with something stronger, and hence their high breath alcohol reading!Where possible, never allow the subject to eat or drink ANYTHING prior to a breath test. But in situations where this cannot be avoided, always then allow a period of at least twenty minutes to elapse before proceeding with the breath test.
• Is it true that the breathalyser test just measures the alcohol that is in a person’s stomach, from their last drink?
  • NO: when we inhale, oxygen passes from the incoming air into our blood, and carbon dioxide passes in the reverse direction. This gaseous exchange process occurs most efficiently deep down in the lungs, where the air is at its warmest and where there is the greatest contact between the blood and the breath. If alcohol is present in the blood – and because it is volatile – some of it will evaporate from the blood into the breath. The important things is that although only a small portion of the alcohol actually evaporates, the proportion that does so is known is known to be a 2,300th part. This means that the ratio between the breath and blood alcohol concentrations in the lungs is relatively constant, even between individuals. It is this alcohol that has evaporated from the blood that we are measuring during the breath test, because its concentration is strongly related to the blood alcohol level. So breath analysis has nothing to do with any alcohol that might still be in the stomach, it actually provides a reliable measurement of what is actually present in the circulating arterial blood.
• What is the blood:breath ratio, and how constant is it between individuals?
  • There has been, and still is, a lot of discussion on this subject – much of it seriously mis-informed. The ratio of the alcohol levels in deep lung expired breath and the pulmonary arterial blood with which it is in contact is close to 2,300:1 for all individuals. The small deviations from this are a result of abnormally low or high body temperature, and variations in the individual’s blood chemistry [mainly their haematocrit value]. The high and low values of the ratio that are sometimes quoted [1,700:1 up to 3,000:1] are not in fact representative of the partition ratio actually occurring in the lungs at all, but are caused by the fact that they are derived by sampling venous blood, which does not represent the arterial blood with which the breath was in contact. Mathematical artefacts also contribute to these wide ranging values of the quoted blood:breath ratio.It is also worth pointing out that it is the arterial blood that is in contact with the brain, and so which causes the impairment which we are trying to quantify: this means that breath actually provides a better index of this than conventional blood sampling and analysis.
• Is there anything I can take that will remove the alcohol from my breath, so that I can cheat the breathalyser test?
  • There are many myths and legends about various devices and materials that are supposed to remove alcohol from your breath – such as chewing chlorophyll chewing gum or cat litter; or sucking a lemon, a copper coin or an aluminium lollipop. But none of these work!You should also take care when even considering trying to adopt one of these tactics if required to take a breath test. Such an action – even though it doesn’t work, but you adopted it in the belief that it did – could be regarded by the Police and later the prosecuting authorities as an attempt to pervert the course of justice. And the penalties for conviction of this offence are likely to be very serious indeed.
• If the atmospheric pressure is very low at the place of a breath test, such as at high altitude, would this affect the concentration of alcohol in a breath specimen being analysed?
  • NO: a person’s breath alcohol concentration is unaffected by variations in atmospheric pressure – even at high altitude.
• Does the breath test instrument tell me how much a person has had to drink?
  • NOT DIRECTLY, NO. The breath test instrument tells you exactly how much alcohol the subject has in their breath at the time of the test. This level will of course be governed to some considerable extent by what they have had to drink; but many other factors also play a part – such as the subject’s gender and body weight; what they have eaten, and when; over what period they actually drank the alcohol, and how long ago they finished; plus their own personal alcohol metabolism rate.
• What are the units of measurement?
  • Units of Breath and Blood Alcohol Concentration Measurement
    Whenever we take a specimen of breath and measure its alcohol content, the most obvious [and most logical] method of expressing the result of that analysis is simply to define the weight of alcohol that is present in a certain volume of breath. And in fact, this is now how it is done in most countries. But there are several units of measurement in common use:BREATH Alcohol Concentration Units
    There are FOURof these in use in various countries around the world:Micrograms of alcohol per litre of breath
    Usually abbreviated as – µg/L [or µg/l, or µg/1000ml, or µg/1000mL]This unit of measurement is currently used in, for example, New Zealand, the Netherlands and Botswana.
    A typical format for a measurement result expressed in this unit is 350, with the likely range being from 0 to 2,000.Milligrams of alcohol per litre of breath
    Usually abbreviated as – mg/L [or mg/l]
    This unit of measurement is currently used in most of Europe, as well as in many other countries; such as South Africa, Taiwan and Japan.A typical format for a measurement result expressed in this unit is 0.35, with the likely range being from 0.00 to 2.00.Micrograms of alcohol per one hundred millilitres of breath
    Usually abbreviated as – µg/100ml [or µg/100mL, or µg/%]This unit of measurement is currently used in the United Kingdom, Ireland, Cyprus and Singapore.

    A typical format for a measurement result expressed in this unit is 35, with the likely range being from 0 to 200.

    Grams of alcohol per two hundred and ten litres of breath

    Usually abbreviated as – g/210L [or g/210l]

    This unit of measurement is currently used in the United States and Australia.

    A typical format for a measurement result expressed in this unit is .080, with the likely range being from .000 to .600.

    BLOOD Alcohol Concentration Units

    Milligrams of alcohol per one hundred millilitres of blood

    Usually abbreviated as – mg/100ml [or mg/100mL, or mg/%]

    This unit of measurement is currently used by the United Kingdom, Ireland, Cyprus, Singapore, Malaysia, Thailand, Canada, and by most countries in the Middle East.

    A typical format for a measurement result expressed in this unit is 80, with the likely range being from 0 to 500.

    Grams of alcohol per one litre of blood, Promille [w/v]

    Usually abbreviated as – g/L [or ‰ w/v]

    This system is used throughout much of French-speaking Europe, as well as in Spain and Portugal.

    A typical format for a measurement result expressed in this unit is 0.80, with the likely range being from 0.00 to 6.00.

    Grams of alcohol per one kilogram of blood, Promille [w/w]

    Usually abbreviated as – g/Kg [or ‰ w/w]

    This system is used throughout much of German-speaking Europe, and Scandinavia. When converting from this measurement unit to another it is necessary to make use of the specific gravity of whole blood, which is 1.06.

    A typical format for a measurement result expressed in this unit is 0.80, with the likely range being from 0.00 to 6.00.

    Grams of alcohol per one hundred millitres of blood]

    Usually abbreviated as – % BAC [or % BAL, or g/100ml]

    This system is used throughout the United States, Australia, South Africa and Korea.

    A typical format for a measurement result expressed in this unit is .080, with the likely range being from .000 to .600.

    Millimoles of alcohol per one litre of blood]

    Usually abbreviated as – mmol [or m.mol/L, or mmol]

    This system is used throughout much of the medical fraternity, most typically in pathology.

    When converting from this measurement unit to another it is necessary to make use of the molecular weight of ethanol, which is 46.

    A typical format for a measurement result expressed in this unit is 17.4, with the likely range being from 0.0 to 99.9.

• How do I convert between units?
  • CONVERTING FROM BREATH TO BLOOD ALCOHOL UNITS
    In some countries it is still the practice to convert the result of a breath alcohol analysis to a blood alcohol concentration. In order to do this use must be made of a blood:breath ratio. There is much dispute and debate on this subject [much of which is now significantly out of date and misinformed], which means that different countries have each adopted their own assumed value of this ratio when preparing this legislation – such as 2,000:1 in France and Scandinavia; 2,100 in the USA, Australia and Korea; and 2,300:1 in the United Kingdom, Malaysia and Ireland.