Connected to the episode s06e04. Was there any fuel spilled inside the hut when Daenerys set it on fire?
Those braziers she tips over are full of oil... which is a fuel. This is why the fire splashes across the floor when the braziers fall over. They're giant, open oil lamps.
As the oil splashes out and hits the wood of the hut, it helps spread the fire quickly because it's designed to burn.
Haven't found any direct confirmation but this Daily Kos episode recap article has the same interpretation:
Challenged, insulted, and threatened with both gang rape and horses (how do you get a horse to … never mind) Dany casually grabs the edge of the nearest brazier and tips a few gallons of burning oil toward the khals. She then repeats this maneuver several times, turning the massive tent into a billowing pyre and crisping every Dothraki leader in one neat package. And she does it without even needing a dragon.
To add to this, don't forget that this is likely happening in some form of compressed time (because movies are magic). We see it happen over two and a half minutes but, realistically, it was likely at least 10 minutes if not 15-20 minutes as that gives enough time for everyone from the entire camp to assemble and for the entire building to be consumed.
Did Danny not imply there was a role for the young widow she was with when she was being 'rescued'? I took it to mean that she was directed to spread something flammable on the ground beforehand...the director went to some lengths to show the fire spreading across a hard surface...j
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There probably didn't need to be any fuel spilled in the hut, as the hut was made out of fuel.
That being said, the braziers appeared to have some oil in them which spread across the ground quickly once tipped over. Take a bunch of dry wood and grass and apply some burning coals to it. It will light on fire. Take that same wood, pour lighter fluid on it first, and it will burst into flame.