Some people say it wont get hot enough some say it will. One thing I don't get is people put tin foil on their grills and cook stuff on it all the time, and the tin foil would be getting WAY hotter that way than if you're smoking out of it. And then you'd be eating the stuff. And is it true that even if it does get hot enough, all you might get is Alzheimer's?
Is it safe or not?
Two things here...
When people say something vaporizes, or ignites, or freezes, or whatever thing based on temperature happens based on temperature... that is a bit of a simplification.
Usually these changes occur based on the energy, which temperature is basically a measure of. But if you look at one block of aluminum, your talking about a shit ton of tiny atoms. All of these atoms are at slightly different energy states... and while it may take a high temp to produce the bulk of the dangerous vapors, some will be produced at lower temperatures too. Its kinda like how water boils at 100 deg Celsius... but really some will evaporate at much lower temperatures.
Second, when people cook with aluminum foil they do not close the grill, hook a hose up to it and take fat drags off it... so any dangerous effects mostly dissipate into the atmosphere. For what its worth I know people who wont eat food cooked in foil.
I have also smoked out of foil pipes in my younger days when there were no options... So its not like one breath will kill you, but prolonged exposure is bad and repeated use is probably unwise.