90A-2015 220.127.116.11 requires smoke dampers to isolate the air-handling unit from the remainder of the system (the ductwork) in order to restrict the circulation of smoke. I had thought this was to keep smoke from a fire within the AHU (fan motor windings or fan belts are about the only thing that will ever smoke inside the unit) from getting to the occupied space. But the exceptions allow you to not have the smoke dampers if the AHU is only connected to a single occupied floor. So I guess that the 18.104.22.168 requirement is not there to protect occupied spaces from smoke generated within the AHUs, otherwise we would protect the single floor also. So really we are concerned about ductwork connecting two floors and smoke moving between floors; so what is the point of having smoke dampers at the AHU? We should be looking at having smoke dampers in ducts that connect the floors (which we already do). Seems like I could have an AHU that sits on the roof and serves the two floors below it and I could meet the stated intent to isolate the AHU from the lowest floor with smoke dampers just at the floorline between the upper and lower floor and not have any smoke damper between the AHU and the upper floor. The Standard doesn't care if we smoke out the upper floor anyway. I didn't see any discussion threads on issues related to this paragraph and toss this out for your thoughts. Thanks.