I'm not sure that there are any
guide lines, but blackouts can definately happen if there is heavy drinking going on. Alcoholism appears to take a heavy toll on the memory. And I agree with lyn, my ex-alcoholic seemed to have memory lapses drunk or sober. If there is even a question as to whether or not a person is blacking out, it is a sign that there is a serious problem.
Peace,
Gabe