Torrent of Embers

Create an out pour of fast moving embers in the direction you point, deals 2d6 fire damage on a successful attack against AC however if used against a construct or obstacle it is considered a guaranteed hit and instantly ignites the obstacle causing a huge conflagration of flame. This will fully destroy the obstacle in two turns (or two minutes) for each size category it is above small, i.e. a small obstacle takes two turns to be destroyed, a medium one takes four turns etc. 

Any attempt made to extinguish the flame from any means other than a spell of 4th level or higher has disadvantage.