As for Tatupu specifically, check out this calculator:
Intoximeters Drink Wheel / Drink Calculator for Breath Alcohol Testing / Breathalyser / Breathalysers / Screener / DUI / DWI / Ask DOTti
According to that, at 242 lbs, he would have to drink 12 beers in 2 hours to blow .15. However, this was at least 1.5 hours after he stopped drinking, so it was probably more than that. Any non-idiot should know that you can't drink half a case and then hop in the car.