Jones, A.W (1985. J. Anal. Toxicol. 9:246) found endogenous levels are from undetectable up to 0.02 mg/dl
Lester, D. (1962 Quart. J. Stud. Alcohol 23:17) found they could be up to 0.15 mg/dl
Compare with legal limit of 80mg/dl for a car driver, and 20mg/dl proposed for airline pilots. Not even close, better excuses needed ...