Why need to breath continuously more than 3 seconds during breathing alcohol test?

If the breathing time is too short, the alcohol molecules in the blood haven’t fully fissused into the lungs. At this time, the test results are affected by the original gas in the respiratory tract, and there will be a big difference with the actual alcohol content in the Blood.( According to National standard GB-T 21254-2007, the breath sampling time is required to be no less than 2.5s during alcohol test, and the EU standard required is no lesss than 4.85s.)