Inspired by this youtube demonstration by ChemicalForce, I'm prompted to ask what is the coldest possible flame.
What the video seems to show is phosphorus vapour in an inert gas being blown into air. This seems to create a flame, but one so cool you can hold a finger in it and not be harmed.
So is this the coolest known flame or are there other known phenomena that are cooler?
NB I suspect that flame temperature depends not just on the stuff that is burning but also on the details of the flow and concentration, so please specify what they were if there are other candidates.