The Machines 

 

There are a wide variety of different makes and models of "chemical breath test" devices used in the United States.  In NYS (outside of NYC) there are two basic machines in use: 1) the Draeger "AlcoTest;" and, 2) the DataMaster. Two models of AlcoTest units are used, the Model 7110 and the Model 9510.  The 9510 is the latest model and is used statewide by the NYS Police.  Some local departments may use a unit other than the AlcoTest or DataMaster.  Both devices attempt to measure the amount of alcohol vapor in the subject's breath (abbreviated as BrAC).  The machines then convert this measurement to a supposedly accurate measure of the amount of alcohol in the subject's blood (which is what the law refers to).

 

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How The Machines Work

 

Both the AlcoTest 9510 and the DataMaster primarily use a technology known as "infrared absorption." This is based upon the scientific principle that different gases will absorb infrared (IR) light at different wavelengths.  The machines operate by having a breath sample brought into a chamber where an IR light source passes through the breath sample and a mechanism then measures how much light is absorbed at certain wavelengths that ethanol (alcohol) is known to be absorbed at. The more alcohol vapor in the chamber the greater the amount of IR light absorption that occurs.  

 

Based upon the measured amount of light absorbed at the prescribed wavelength machines then calculate the amount of alcohol vapor is present in the breath sample.  They then convert that measurement into a percentage of liquid alcohol in the blood using a fixed formula. This conversation relies on an accepted scientific rule known as "Henry's Law," which postulates that the relationship of a chemical in a vapor found above a liquid will be proportional to the amount of liquid of that chemical in the total volume of the liquid. Thus, Henry's Law says that if the vapor above a liquid contains 10% of a certain chemical's vapor that chemical must make of 10% of the total volume of the liquid.

 

The DataMaster units rely totally on IR absorption to calculate BrAC.  However, the AlcoTest units utilize a second system that operates in parallel to the IR system.  The second system uses a different technology called "Fuel Cell" conductivity.  This system uses the ability of a Fuel Cell to increase or decrease its ability to conduct electricity.  The more alcohol that is present in the sample the greater the change in conductivity of the Fuel Cell.  Again, like the IR system once it has calculated the amount of alcohol in the breath sample it relies on Henry's Law to convert that to a blood alcohol percentage.

 

Both the DataMaster and the AlcoTest attempt to verify that they are working properly by going also testing a known sample of alcohol vapor either prior to the driver's breath test and/or immediately after.  That sample (known as a Simulator Solution or Simulator Sample) is generally tested by a laboratory before it is sent to a police station.  The samples are usually set to contain .10% alcohol and the machines should read that sample within + .01% of the laboratory tested amount.

 

Problems With Chemical Breath Test Devices

 

While the police and prosecutors frequently refer to chemical breath test (CBT) machines as "instruments," in fact, they are not.  They do not measure the amount of alcohol in the blood, they measure alcohol in the breath and they may or may not do that accurately and the conversion to a blood alcohol amount may or may not be accurate, either.

 

For example, all CBT are set up to very carefully control the temperature of the simulator sample used because warmer air can hold more vapor and colder air can hold less.  However, they have no such mechanism to control the temperature of the actual breath sample from a driver.  Instead, they assume that everyone has the same temperature breath, which isn't reality. Thus, someone who's breath is warmer than average can have more alcohol present in it than someone who's breath temp. is average or below.

 

Second, the manufacturers of the CBT devices admit that they are only accurate with a range of + 10% of the value read. Thus, a .08% machine reading is actually anywhere from .07% to .09%.  

 

Third, the machines rely on Henry's Law which only deals with liquids.  However, blood is made up of both liquids and solids (white and red blood cells).  The amount of the blood that is made up of solids varies greatly from one person to another.  But, the machines assume that everyone is the same.

 

Fourth, the machines supposedly only measure alcohol vapor from the "deep lung" of the driver because alcohol in much greater concentrations may be found in the mouth (especially for people wearing dentures), in the throat or the bronchial passages. The machines supposedly can correct for alcohol that is not from the deep lung, but that can't really be proven.

In trouble with the law?  We're here to help.  Call us now for a free phone consultation: 845-294-0585

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Copyright 2013 - Law Offices of Glenn W. Magnell

Please note: Information on this website is intended to inform, not to advise. No one should attempt to interpret or apply any law without the assistance of an attorney that is familiar with that area of law, the rules of the court involved and the specific facts of each individual case.

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Glenn W. Magnell
Law Offices of Glenn Magnell
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