Here Lion's experts answer many of the questions that we regularly get asked about alcohol in the body, testing for alcohol in the breath, and Lion's breath analysis equipment.

FAQ’s : The Science of Breath Analysis

• 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.