I agree. A 48" wide slider may not give you the 20" clear opening width needed for egress. A slider doesn't open a full 50%. Plus, you subtract the frame dimension and it will be close depending on the particular brand window.
Another suggestion would be a european style tilt-n-turn window which many manufacturers carry.
It's a dual operation window that opens up like a door for egress and also tilts in from the top for secure ventilation. They are available as a single sash window or as a french swing window as shown below in which both sashes open wide. This type window would be a much safer choice for easy egress.