Ugh, sorry about the fire, that bites. Hopefully it’s all superficial damage.
Anytime you’re layering material - no matter what it’s made of - there’s an increased chance of fire. A thin sheet of tinfoil over your riser material may help some, but it’ll increase flashback. OTOH, risers that have very little material in contact may solve your problem entirely.
This thread starts with a 3D printed set of risers, but further down there are a few different options for laser cut versions 