Limiting travel distances - Means of Escape:

Some buildings, or parts of buildings, do not have alternative exits and do not have protected escape routes leading to a place of safety.  

Such building layouts can be acceptable provided that everyone is able to pass a fire whilst the fire is still very small.

For example, rooms (except for large rooms) usually only have one door so the first part of the escape route, for anyone in the room, has no alternative and is unprotected. it is across the open room.  To ensure that this can be guaranteed to be a safe route the travel distance across the room is limited.  By limiting travel distances it is ensured

that the number of people that can fit in a room is limited and it is also ensured that the people in the room are not very far away from the exit.  By doing this it is ensured that, even if a fire were to start near to the exit from the room, everyone could get out of the room before the fire grew large enough to cut off the escape route.