From a recent thread by Chef JJ....
Sorry Guys but...IT JUST DON'T MATTER! Chicken on top, Chicken on bottom? Don't matter...Let's look at the Worst Case scenario.
You are smoking a rack of Ribs, 225°F, at the 4 hours mark you put a whole drippy Chicken on top for a 2 hour smoke. Red Bacteria laden Chix juices are oozing all over the Ribs...ONE MINUTE later you realize the smoker temps were higher than you thought, this whole time the smoker was at 275°F, and Those Ribs Are Done! You immediately remove the Ribs...Any Problem here???? Is a trip to the Hospital certain??? NOPE!
The " surface " of those Ribs are 275°F! There is not a single Bacteria known to man that can survive more than few SECONDS at 165°F !!! There is just No Way the Salmonella, or anything else, see Dave Omak's chart below right column, could possibly survive contact with the 275°F surface of the Ribs. ALL Bacteria are Instantly killed and there is no chance of food-borne illness eating those Chicken basted Ribs...Even with Rare Steak. Bacteria can't Bore into the happily cool center and the Surface is 275°...More than instant Death to all!
Ok...There is mentally some YUCK factor because raw Chicken juices dripping sounds nasty but no Safety issues exist. In every other case the Chicken and other meat will be in the 225+ temps for hours. Above or below, again all bacteria is killed...JJ