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Why Breathalyzer Tests Aren't Always Reliable

No matter what highway patrol officers tell you, roadside breathalyzer tests are not infallible. In fact, the small pocket breath alcohol testing devices are notorious for being inaccurate and unreliable. So if you have been put in cuffs or charged with driving under the influence (DUI) due to the results of a breathalyzer, our Santa Rosa DUI defense law firm is here to tell you a few things you should know about them that could help protect your driving privileges.

Margins of Error & Partition Ratios

The world’s best breathalyzer device will still have a margin of error around 0.01 percentage points. This means that if a person’s actual blood alcohol concentration (BAC) level is 0.04, the breathalyzer could show any number between 0.03 and 0.05. Considering that most people are legally considered intoxicated at 0.08, the margin of error could technically be considered as 12.5% – or one-eighth of the percentage points that matter. Such a high margin of error in any respectable lab report usually means the results are unusable.

Furthermore, a breathalyzer device doesn’t actually directly measure a person’s BAC level. Instead, it detects miniscule amounts of breath alcohol in a person’s exhalation and multiplies that number by a partition ratio. The preset partition ratio for most breathalyzers is 2,100:1 but this is not the same partition ratio for every person.

Physiological factors that can change a person’s partition ratio include:

  • Weight-and-height ratio
  • Sex and age
  • Breathing pattern and resting heartrate
  • Average body temperature

Ever-Present Mouth Alcohol

Breathalyzer tests are supposed to only measure breath alcohol, or particles of ethanol in breath directly exhaled from the lungs. If there is the slightest trace of alcohol in the person’s mouth, or churning in their stomach, it can contaminate the results by spiking the reported BAC amount. Officers are supposed to give a person 15 to 20 minutes to rest under constant observations before administering a breathalyzer test; if the DUI suspect burps, vomits, or chews on anything during that time period, no test should be conducted. However, many people arrested for a DUI can attest that this “deprivation period” never occurs.

Working with a Professional Lawyer

After your chance at a fair trial or administrative hearing has been sullied by an unreliable breathalyzer test, you can rebalance the scales by contacting the Law Offices of Evan E. Zelig, P.C. Our Santa Rosa DUI attorney has more than a decade of experience protecting clients from the excessive penalties of the criminal justice system brought about by misled or inaccurate prosecutions. Call 707.418.5352 to learn more about your rights and legal options from a professional team who cares about your future.