Nearly all Rochester drivers stopped for drinking and driving will be asked to submit to a breath test to determine their blood alcohol content.

Breath test machines have been in use for decades, and the science behind them has evolved during that period.

Many modern breath test machines – including most of those in use in the Rochester area – rely on a method of detection known as infrared (IR) spectroscopy to determine the amount of alcohol in a breath sample.

The underlying scientific basis for IR breath testing is theBeer-Lambert Law of Absorption, which states that different types of molecules absorb electromagnetic radiation at certain specific, unique wavelengths.

For example, water molecules will absorb IR energy at different wavelengths than alcohol molecules.

As a result, each type of molecule has its own, unique infrared fingerprint.Ethyl alcohol – the type of alcohol people consume – absorbs radiation at wavelengths of approximately 3.00, 3.39, 7.25, 9.18, 9.50 and 11.5 microns.

No other type of molecule absorbs radiation at the exact same wavelengths.

As a result, infrared breath test instruments are able to determine the amount of alcohol in a breath sample by exposing the breath sample to a known amount of IR energy and measuring how much of that energy is lost at wavelengths where alcohol is known to absorb IR energy.

The more alcohol the sample contains, the greater the degree of absorption and the more IR energy loss.

Unfortunately, breath test machines that are capable of measuring absorption at all wavelengths where alcohol absorbs infrared energy would be very expensive.

As a result, these machines typically only measure one wavelength where alcohol is absorbed and, while generally accurate, are not foolproof.

Following a DWI arrest, it helps to have an experienced lawyer who understands how the breath test works. Call us at 585-484-7432 for a legal consultation.