Principal chief conservator of forests S K Pande said on Friday that the continued dry spell resulting in low humidity and increased temperatures had caused resinous vapours in the state's pine zone making them a virtual tinder box. Holding these two factors responsible for the spate of forest fires in the state, he said the atmosphere had become so inflammable that even sparks from the exhaust of a vehicle were enough to start a blaze, forget throwing a lighted match, bidi or cigarette.