They shouldn't start a fire unless you are very unlucky and happen to short them to some power lines.

The surrounds look to be about the right height, 2-3' above ear level is the recommended height but if you are running QS's they are very forgiving and many of us run them much higher than that with great results.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70