One of the major differences would be construction requirements and hence the safety factor being increased for Fire Escapes. Fire escapes tend to be constructed more narrow, steeper, etc. and quite frankly scary to walk on if you are three stories up, we have a few here. Therefore part of the increased fire protection. Exterior stairways required by Building Code would fall under building code if existing. If the stairs comply with the OBC of the day then move on and only worry about maintenance. Check with the Building Officials on whether the stairs complied or if they pre-date OBC then perhaps Part 11 of the OBC would help, either way check with them. Call it a fire escape, make sure it complies, get the owner to agree and then go with wired glass for the window openings and be done with it, may be cheaper for the owner and you would be meeting OFC protection regulations for a fire escape – just a thought. Be safe.