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What types of alcohol sensing technology do evidential breath testers use?

 

EBTs use one of the following technologies:

 

Electrochemical Oxidation/Fuel Cell

Most EBTs used for DOT breath alcohol testing use a fuel cell to detect alcohol.  This method of measuring breath alcohol uses special electronic components that generate electrical energy by oxidizing a fuel.  The components, called “electrochemical cells,” or fuel cells, consist of two platinum electrodes.  When alcohol passes over the surface of the fuel cell it generates a small electrical current.  The electrical current is then used to measure the alcohol concentration.

 

How Does a Fuel Cell Work?

When breath containing alcohol molecules comes into contact with the fuel cell, a spontaneous flow of electricity is generated.  The amount of electrical current generated indicates how much alcohol is present in the breath sample.  The end result is the alcohol measurement displayed on the EBT.

 

Infrared (IR) Spectrometry

Infrared devices measure the amount of light that is absorbed by the alcohol molecules present in a person’s breath.  Alcohol molecules absorb light at specific frequencies.  In IR devices, a light source focuses on a sample chamber.  The light passes through a series of filters and finally strikes a detector in the sample chamber.  When a person blows into the mouthpiece, the breath passes into the sample chamber.  If alcohol molecules are present, the alcohol molecules absorb the transmitted light at certain frequencies.  Less light reaches the detector.

 

How does an IR device work?

As the amount of alcohol molecules in the chamber rises, the amount of light reaching the detector falls.  This is an inversely proportional relationship. (A similar one is a smoke-filled room.  The more smoke that enters the room, the less you can see.  In the same way, more alcohol in the chamber means less light reaches the detector.)  The IR device finds the difference between the zero reference point and the breath measurement and determines a breath alcohol concentration.

 

Gas Chromatography

Gas chromatography is a technique for separating closely related compounds by passing them through an absorbent.  A carrier gas such as hydrogen or helium moves the suspect compounds through the device.  As of January 2009 there are no EBTs being used for DOT alcohol testing that use gas chromatography. 

 

How does a GC device work?

The gas chromatography technique involves three main functions:

  • Injection: Getting the sample to be analyzed into the device. In breath testing, “injection” means providing the breath sample.

 

  • Separation: Isolating particular compounds after the breath sample is in the system.  The carrier gas pushes the compound into a column that separates the substances in the breath.  Picture a coin sorter: coins of different sizes fall through holes to a certain level.  Quarters, the largest coins, will stay on the first level, nickels fall to the second level, and so on.

 

  • Detection: The separated compounds move through the column at different speeds, and are identified by the length of time needed to reach the detector.

 

How are the results recorded?

The detector transmits an amount of electrical current proportional to the concentration of each substance to a graphic recorder.  The printed results show a peak of the line at the highest concentration of the substance.  The time line identifies the types of substances.  Breath alcohol concentration can be determined from the graphic results or obtained directly from a digital readout.