It is standard procedure in Rochester DWI cases for the arresting officer to request that the driver submit to a breath test.

A breath test that results in a finding that the defendant’s blood alcohol content is .08% or greater is considered strong evidence that the defendant is intoxicated and can be very damaging to the defendant’s case.

The ability of a breath test machine to determine the amount of alcohol in a person’s blood depends upon what is termed the Blood-Breath Partition Ratio.

A breath test does not directly test the amount of alcohol in a person’s blood – it directly tests the amount of alcohol in a person’s breath.

The amount of alcohol in a person’s blood is then determined based on the Blood-Breath Partition Ratio, which states that 2,100 ml of breath contains the same amount of alcohol as 1 ml of blood.

All breath test machines rely upon this 2,100:1 ratio when determining blood alcohol content.

This ratio was set by the National Safety Council’s Committee for Tests on Intoxication over forty years ago.

Unfortunately, it is only an average figure which does not account for normal human variation.

Studies have found that the actual ratio can vary from 1,100:1 to 3,000:1.

A lower than average Blood-Breath Partition Ratio will result in a higher result when taking the breath test, even though the machine is working properly.

Because it relies on an assumed Blood-Breath Partition Ratio where the individual’s actual ratio is unknown, a breath test cannot be as accurate as a blood test in determining blood alcohol content.

If you have been arrested for drinking and driving and took the breath test, it is important to consult with an experienced DWI lawyer, call us at 585-484-7432.