Some great questions and something I have little experience with but have a good understanding of electrical wiring and fires.

Being a fire or safety hazard would depend on many things but since most materials would need much more heat to create a fire than 114 degrees, a spark would probably need to occur to ignite anything near the UTH.

I have never experienced any over heating issues with UTH use, but can see in some of my snake enclosures where the heat has left permanent burn marks right through the enclosures resin bottom. Whether this was due to no air circulation under the tank, or what was on top of the heated area, I can not say since it occurred long ago.

As for plastics, I believe that they can get hot enough to melt plastic if not air circulation is provided but still think it would not create a fire hazard only due to the heat the UTH is generating.