Breathalyzer Machines

Breathalyzer Machines

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The "Science" of Breath Machines

A breathalyzer machine attempts to measure alcohol in a person's breath. From the "get go" under Missouri law, the logic of a breath test (which is the test used in the majority of cases) can be questioned because Missouri DWI law is based on the blood alcohol content of the driver at the time of driving.

A breath testing machine measures the alcohol in a person's breath and then estimates, with a formula, the amount of alcohol in the person's blood.

The machines assume that a person (without taking into account any individual variations) has as much alcohol in 1 milliliter of a person's blood as he/she does in 2100 milliliters of lower "alveolar" air (air from the lowest part of the lung).

Therefore, if you are stopped for a DWI in St Louis, and you are not a "normal" subject, such as anyone with a lower lung capacity (for example most women, individuals with COPD, pulmonary problems, asthma, or any other divergent factors), the assumptions and estimates of your blood alcohol content are possibly wildly incorrect---and therefore, subject to challenge.

Moreover, the officer administering the test should have told you, pursuant to the procedures mandated by the Missouri Department of Health to "blow long and steady into the tube until I tell you to stop."

If you were given the improper instruction on how to blow, the results of your test could well be inaccurate.

Problems with the Breathalyzer machines

Each of the three approved breathalyzer machines in use in Missouri have problems.

  1. BAC Datamaster - has problems with distinguishing mouth alcohol from breath alcohol. Therefore, if you chewed gum, for example, before a breath test, it could have affected the result.
  2. Intoxilyzer 5000 - false readings occur if the subject blows too hard, the electronic noise can cause a high false reading, and the machine has a limited ability to detect Radio Frequency Interference, causing high readings. The machine is so inaccurate, that although the manufacturer claims the machine is 95% accurate, one court has found that this machine is only 52% accurate.
  3. Alco Sensor IV - Diabetics and dieters on very low calorie diets can give false high readings. This machine is susceptible to temperature variations, especially in the winter months.

"Rising" Blood Alcohol Content Defense

Another issue to be considered in breath testing analysis is whether your blood alcohol content (BAC) had risen from the time you were arrested to the time you took your breath test. A Missouri arrest for Driving While Intoxicated is just that - being intoxicated at the time you were driving. It is not an arrest for being at the police station while intoxicated.

Absorption is the process by which the body absorbs alcohol, through the stomach/large intestine and carried in the blood to the brain. If you have ever had a drink of alcohol, you know this takes time. Breath testing is postabsorptively premised. Breath testing during the absorption phase is not accurate.

The highest BAC is usually found at 30-60 minutes after drinking alcohol. However, if large amounts of alcohol are consumed in a short period, or if large quantities of food are eaten at the time of alcohol consumption, the absorption process could take up to 2 hours after the drinking.

Therefore, depending on when and what you drank/ate, when you were arrested in relation to the drinking/eating, and when the breath test was conducted in relation to the drinking/eating, your BAC could have been steadily rising during this entire time.

Therefore, it could be you had a breath test that resulted in, for example, a BAC of .10%, yet your BAC at the time of arrest was under .08%.

All other things being equal (such as weight, gender, food consumption, medications used at the time), this defense may be viable where it can be shown the driver's drinking began and ended shortly before the arrest and his or her breath test was conducted 20-60 minutes following the arrest.

Mark Dean understands the science of DWI law. We can assess the probable reliability of your breath test result based on a number of factors. We are skilled at pointing out these weaknesses in the prosecutor's case, and, if need be, we can employ the proper expert(s) to testify that your breath test was invalid.

Please contact The Law Offices of Mark Dean for a free phone consultation (followed by a free 15 minute in person office consultation) at 314-675-0000 or 1-800-431-3212.




12747 Olive Blvd, Ste. 300
St. Louis, MO 63141


3000 South Jefferson, Suite 2009
St. Louis, MO 63118


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Chesterfield, MO 63017


912 S. Fifth Street
St. Charles, MO 63301


1610 Des Peres Road, Suite 150
Des Peres, MO 63131


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314-675-0000   |   800-431-3212


The Law Offices of Mark Dean is a Personal Injury Law Firm and Workers Compensation Law Firm based in the St. Louis, Missouri area and provides legal services in personal injury and workers compensation. The Law Office of Mark Dean represents and counsels clients in the entire State of Missouri including St. Louis City and the counties of St. Louis, Jefferson, and St. Charles, as well as in surrounding cities that include Wildwood, Ballwin, Kirkwood, Webster Groves, Affton, Arnold, Manchester, Concord, Crestwood, Town and Country, Richmond Heights, Murphy, Sunset Hills, Park Hills, Eureka, Brentwood, Sappington, Shrewsbury, Valley Park, De Soto, Glendale, Rock Hill, High Ridge, Frontenac, Green Park, Byrnes Mill, Marlborough, Winchester, Hillsboro, Oakland, Lakeshire, Allenton, Dittmer, Ellisville, House Springs, Twin Oaks, Wilber Park, and other areas. Managing Attorney Mark Dean also is licensed in the state of Illinois and provides Illinois Personal Injury legal services to clients in the entire State of Illinois, including Edwardsville, Belleville, Collinsville, Madison County, St. Clair County, Springfield, Peoria, Chicago, and Cook County.