Fire safety for internal bedroom windows?

Thanks in advance!

We have three bedrooms that open onto a landing with a single staircase down. 
we want to put an internal window in the wall of the smallest bedroom, to let light in the hallway. The window will look onto the staircase (so, it will be fixed but if it wasn’t and you jumped through it, you’d fall to the ground floor, through the stairwell).  Does this internal window need to be fire-rated? And is there a limit to how big it can be/where it can be? We’re either going to go with a fixed long letterbox window along the top or a big round window, fixed too.