Ok… i have maybe a start of explanation… but i have not have much time for test the result ( too much work )…
create a plane ( in my case 1:1 ) … in edit mode, use subdivide…
Modifier " decimate " … iteration 1, apply the modifier. ( not needed if the mesh need to stay straight )
In edit mode… select all ( a ) and delete " only faces"… you will obtain a 2D mesh
Now this is where the thing start too be tricky… I was think first to use solidify, but the problem is the normal are going crazy.
So i have decided to try it differently… convert mesh to curve > and play on resolution depth etc for get the soldifiy effect, then you can come back to a mesh ( convert curve to mesh, dont forget to remove doubles )…
Now, with the shape of your fireguard, before creating the 3Dmesh, i will create the shape of the fireguard, then use shrinkwarp modifier on it with the 2Dmesh… and then apply it, convert to curve > add tthe depth ( for obtain a 3Dmesh ( remove doubles ) and then convert it back to mesh.
Im sorry i cant testt it fully right now, but well i hope it can give you some idea.
Now as some have pointed it, 3Dprint a so dense mesh require a 3Dprintter who is able to print a mesh at this size. the only ones i know who are capable of this are for medical printing. YOu will need too check the minimum size it can print.