Lol the motherboard box=case is great for most stuff but i can see it being a little dangerous for mining rigs.

However, we're generally talking about temps below 100C for the CORE of the GPU, and I'm sure the air is quite a bit cooler than that.  Paper burns at ~541F (thanks Bradbury) and cardboard is closer to 800F.  I'm still new to this but fire seems pretty unlikely if you keep your setup free of clumped dust.  If anyone has any horror stories than please share (not to correct me, but because i want to hear them )