What is the standard breath sample volume used to determine alcohol concentration in a breath test?

• A. 210 liters
• B. 100 milliliters
• C. 67 milliliters
• D. 1 liter

Answer: (A)

Breath testing relies on analyzing alveolar air, the end-expiratory portion of a breath, to reflect the blood’s alcohol level. To get an accurate reading, you need a deep, complete exhalation that yields a sufficient volume of breath—about one liter for the sample. This volume is large enough to include alveolar air and minimize the influence of dead space air from the upper airways. Smaller samples won’t reliably represent the blood alcohol concentration because they miss the representative alveolar portion.

The measurement itself depends on a standard conversion, not the sample volume, using a blood-to-breath partition ratio of about 2100:1 to translate breath alcohol concentration to blood alcohol concentration. A number like 210 liters isn’t attainable from a single exhale and isn’t used as the standard sample volume. So, the practical standard breath sample is around one liter of breath.