Breathalyzers

Alcohol that a person drinks shows up in the breath because it gets absorbed from the mouth, throat, stomach and intestines into the bloodstream. Alcohol is not digested upon absorption or chemically changed in the bloodstream. As the blood goes through the lungs, a physiologically predictable amount of the alcohol will move across the lung membranes and into the lungs themselves.

Once in contact with the air in the lungs, it evaporates and is exhaled. The concentration of the alcohol in the air in the lungs is directly related to the concentration of the alcohol in the blood.

The ratio of breath alcohol to blood alcohol is 2100 to 1 (and called the partition ratio), so the alcohol content of 2100 milliliters of exhaled air will be the same as for 1 milliliter of blood. The math is simple from there and leads to BAC expressed as a percentage of alcohol in the blood.

Factors Affecting Breathalyzer Accuracy

Breathalyzer only estimate the blood alcohol content (BAC) they do not physically measure it, so there are several factors that can cause the breathalyzer to give either an artificially higher or lower reading. The most common are:

• Body temperature and blood composition as outlined above.
• Some breathalyzers can't differentiate between ethyl alcohol and other compounds of a simple chemical nature. Methyl compounds such as acetone and ketones can be present in the breath of diabetics and those taking dietary supplements, causing the breathalyser to over-estimate the BAC. Similarly vinegar can cause confusion with some of the older or dumber breathalyzers. Envronmental substances in the vicinity of the breathalyzer including compounds found in lacquer, paint remover, celluloid, gasoline, and cleaning fluids can also effect the reading in older breathalyzer.
• Breathalyzer assume that the alcohol concentration in the breath will be the same as in the blood, and that the breath is sourced from deep in the lungs, but the breath alcohol concentration can be increased by vomit or blood in the mouth, acid reflux, or simply having had a drink recently with alcohol residue from that drink still being in the mouth at the time of testing. Mouthwash or breath freshener often contain alcohol, so don't use these in an attempt to disguise the smell of alcohol when being pulled over.
• Electrical interference from cell phones and police radios.
• By law, police breathalysers are required to be calibrated for a particular ambient operating temperature, and nearly all are. The problem comes in areas that experience cold winters - while the breathalyzer may be calibrated for the correct outside temperature, if its taken out of the nice warm patrol car and used immediately it will not have had enough time to cool down to its calibrated operating temperature and will give an artificially high reading.
• Absorption of alcohol into the blood may lag actually drinking it by as much as 1-2 hours so even though you may have alcohol in your breath, if you've only consumed it recently it may not be in your bloodstream in the concentration that testing your breath indicates.

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