Alcohol is either digested and metabolized by the body or excreted in sweat, urine or breath. On an empty stomach, the average man absorbs 20% of the alcohol straight into his bloodstream. Experts estimate that the average man will break down alcohol at the rate of 0.015 BAC per hour.Thus, if your BAC is 0.030, it would take 2 hours to have all the alcohol leave your system. Some breathalyzers are faulty and will give you inaccurate readings due to body temperature, acid reflux or a bloody mouth.Natural compounds, like ketones can be mistaken for alcohol in the blood stream also.lcohol is either digested and metabolized by the body or excreted in sweat, urine or breath. On an empty stomach, the average man absorbs 20% of the alcohol straight into his bloodstream. Experts estimate that the average man will break down alcohol at the rate of 0.015 BAC per hour.