There are strong evidence that there exist a correlation factor of 2100/1 between Blood Alcohol Contents (BAC) and the Breath Alcohol contents (BrAC). To obtain an accurate correlation the (BAC) and BrAC, a deep lungs breath samples are required. A person's vital capacity (volume of air that can be expelled without collapsing the lung) can range from 1 liter to 7 liters, depending on factors such as age, gender, physical condition, and health.
If a breathalyzer requires too long of a breath sample before testing for the subject BAC, then the risk is that subject may not be able to provide a sufficient breath sample. On the other hand, if the alcohol tester take samples quickly after the subject exhales a small amount of air, then the correlation between breath alcohol content and the BAC will be inaccurate and unpredictable.
In order to achieve a high correlation between breath alcohol content and BAC, most alcohol tester protocols will require a test subject to exhale for 4 - 8 seconds.
Breathalyzers in compliance with DOT requirements must take samples after at least 5 minutes through the exhale.
Some newer and more advanced professional breathalyzers (like the Alcomate Premium) also track the intensity and force of the exhale breath over the first portion of the blowing time to ensure adequate breath volume is delivered. Most professional-grade breathalyzers measure the force of the breath sample to prevent “fake blowing” through the device.