the location of sampling port at emission stack?

urgent! my boss ask me to search for the exact allowable sampling port location on stack (like at least how many equivalent diameter from the bent and how many equivalent diameter from emission outlet) at the Industrial Ventilation Manual(ACGIH), and he gives hint that it can be found at paragraphs regarding stack...
But, I've searched many times and I still couldnt find it any where!! Did anyone know where is the exact page??