Why concrete is best for a ritual room floor?

Last night I was doing a ritual with a couple of other people. And we were using an incense blend that had some large "tears" of frankincense in it. During the middle of the ritual, we were all reminded why carpet, vinyl, and wood are not necessarily the best ideas for a ritual room floor. One of the frankincense tears popped (ok, maybe exploded would be a better description), and hot pieces of frankincense went everywhere. Fortunately, the floor is actually just painted concrete (the carpet was yawked out a year or two ago); so no harm was done, though it was a valuable reminder that burning resins can be dangerous.