I have a chiminea on my wood deck. It is on a 3' square slab of
bluestone. If a roaring fire is going, once in a blue moon an amber
will make it off the bluestone. The fire pits are more exposed to the
wind, then again, they have the screen. So the bottom line is same as
anything else. There is a certain amount of risk involved, as long as
you understand and mitigate it (i.e. don't leave it unattended), you
will not have a problem. And make sure the embers are really OUT
before you go to bed.

A single ember landing on the deck will at most leave a cosmetic mark
if there is someone watching it. You did'nt build with balsa did you?