FAQ:
The Science of Breath Analysis

The Science of Breath Analysis

Dispelling the common myths and misconceptions about breathalysers and the analysis of alcohol in the breath

NO. Gastric bands are fitted to persons with a weight problem, caused largely by overeating. 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 your breath or blood after drinking alcoholic beverages.

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, resulting in 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.

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 thing 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.

There has been, and still is, a lot of discussion on this subject – much of it seriously misinformed. 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 which causes the impairment that we are trying to quantify; this means that breath actually provides a better index of this than conventional blood sampling and analysis.

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 one of these tactics if required to take a breath test. Such an action – even though it doesn’t work, and you tried  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. The penalties for conviction of this offence are likely to be very serious indeed.

NO. A person’s breath alcohol concentration is unaffected by variations in atmospheric pressure – even at high altitude.

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 unitsof measurement in common use:BREATH Alcohol Concentration Units
There are FOUR of 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 100 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 210 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 100 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 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 100 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.

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.