The breath test is simpler to perform, and administered by non-medical personnel with quicker results. Many situations exist that impair breath tests as a precise calculation of BAC.
Results Used for License Suspension and Criminal Prosecution
All states haveimplied-consent laws. These laws provide that each driver within the state is deemed to have given consent to chemical testing to measure BAC if law enforcement has reasonable suspicion of intoxication. Refusal to submit to testing generally results in license suspension or revocation. See Illinois DUI Law: A Criminal and a Civil Case.
The test results are routinely used in criminal prosecutions, where the penalties can include a loss of freedom. Nearly everyone knows someone that has been arrested for a DUI. Knowledge of the evidence in these cases is important for the public. See DUI Fact Sheet.
From Drunkometer to Intoxilyzer
In 1937, when Rolla Harger invented the "Drunkometer", this invention began an industry that has seen many designs, each trying to advance the accuracy of its forerunner. The Breathalyzer® was invented in 1954 to collect evidence of intoxication by measuring BAC through breath analysis. In addition to Breathalyzer, common brands include Intoxilyzer® and Intoximeter®.
Despite those efforts all breath-testing machines are subject to errors. All breath-testing devices assume the people tested have certain averages, though no individual is average. Human error, maintenance problems, interference from outside sources, and internal malfunctions can affect every breath-testing device.
The Science of Breath Testing
The breath-test measures the amount of alcohol in a deep-lung breath sample. That amount is then translated to BAC. Chemical analysis, infrared spectrophotometry, gas chromatography and fuel-cell detection are the main scientific methods.
With an infrared system, breath is blown into a chamber. Then an infrared beam is shot through the chamber. Alcohol molecules are absorbed by the beam. The beam’s diminution as it passes through the chamber is measured. The more light absorbed, the higher the reading on the machine. This is the theory, though other molecules in the same spectrum as alcohol may also absorb the light. Computer software then translates the results to BAC for the average human.
The Blood:Breath Ratio
This ratio describes the relationship between breath alcohol content and blood alcohol content. It defines the breath quantity that contains the same amount of alcohol as a given blood quantity. The value of 2100:1 is legislatively accepted as the population average. This means 2100 parts of breath contain the same quantity of alcohol as 1 part of blood. The actual range in people runs from 1700 to 3000:1. Also the blood to breath ratio is not constant over time for a specific individual.
Breath testing equipment uses the ratio of 2100:1. Individuals with ratios greater than 2100:1 would have underestimated BAC. Those with ratios less than 2100:1 would have overestimated BAC. The machines make assumptions that may not be accurate for a particular person. See Forcon Forensic Testing.
Individual Variations
Test results are also affected by other issues involving the test subject. These include: age; lung function; overall strength and size; a disease or condition such as asthma, diabetes, eardrum rupture, ketosis, emphysema, bronchitis, dental issues, fever or harelip; shock or trauma; certain types of special diets; or hiccoughing, burping, vomiting or hyperventilating. Heartburn can make breath results unreliable.
Other Technical Issues with Breath Testing
There are technical issues in the conduct of the test itself. These include:
- The machine must be warmed to the correct operating temperature.
- An adequately deep lung sample must be ensured
- The equipment must be maintained properly, calibrated correctly and cleaned adequately.
- Other items such as mouthwash or adhesive, or lip ointment can affect test results.
- Police radios may cause radio frequency interference (RFI) with the testing equipment.
- The subject may have had exposure to a gas or vapor such as paint, floor sanding, varnishing or other chemicals.
- Outside environmental causes in the surrounding air may cause inaccurate test results.
While it is important to protect everyone from drunk drivers, in taking away freedoms or privileges, it should be done with reliable evidence.
