It might come into play that we usually get the tree only a week before the actual date and directly from the forest (which is, I reckon, something not everyone can do), but there must be some other factors, I tell you. I'd guess dry air, high room temperature and bright lights, which all may confuse the tree into "thinking" that it's spring, for starters. Afaik, water is mostly used for transporting stuff, which, if you don't change the soil (or don't even have any), isn't there. Otherwise, the tree shall not cease to live for quite some time, it has its reserves for these reasons exactly - to keep itself alive through several months of winter when every drop of water up to one foot deep might be frozen.
Fire, on the other hand, requires a bit of common sense, namely, everything can go up in flames if left unattended. And so just don't leave it unattended, don't let candles burn down in their holders and place the tree itself in an easily accessible place instead of putting it in the very corner, packed between furniture, like in that video - dammit, people!?
Scotch pine is a different sort of tree, but I can't really imagine that sort of fire going on without other things going up first and that'd be decorations. People burn juniper twigs intentionally, it takes several seconds before it starts. Sparks from crackling needles will sooner light up paper or rug nearby, but the twig itself will resist.