Are there code or safety issues with exposing the area in between your walls for built in shelving?

Construction Walls
1

I have a VERY small bathroom, with no room for shelving. I was thinking of knocking out the dry wall between one set of studs and adding in a narrow set of built in shelves, similar to how medicine cabinets are installed, but not enclosed. Are there safety issues I need to consider?

2

If you want to be careful, use a 2x4 or 2x6 at the top and bottom flush to make a top and bottom plate so fire can’t get up or down wall.

3

Please keep in mind potential electrical wiring, water or gas lines etc…
Sounds mainly cosmetic but if you open that wall up and there is one of the above then code comes into play.