Going the Distance
Remember, distance requirements are specified in the Life Safety Code.
NFPA Journal®, November/December 2008
There are three different distances specified in NFPA 101®, Life Safety Code®: travel distance, dead-end corridor distance, and common path of travel distance. These three distance requirements each look at a different part of the egress issue.
Travel distance is the total distance one must travel from the most remote normally occupied point in a building to the exit. This distance must only be measured to the nearest exit, not to all of them. It represents the total time an occupant will be exposed to fire conditions, as we are generally considered safe when we reach the exit. Usually, the Life Safety Code gives the total maximum distance in Section X.2.6, “Travel Distance to Exits,” of each occupancy chapter. In some occupancies, however, the total travel distance is divided into parts; that is, the distance is measured from the most remote part of the room to the corridor door, then from the corridor to the exit. Examples of such occupancies include health care and educational occupancies.
The second distance specified in the code is the dead-end distance. Dead ends occur in corridors. In fact, the code usually uses the term “dead-end corridor.” The one exception is found in the assembly occupancy chapter, which addresses “dead-end aisle,” but I won’t discuss it here. The Life Safety Code specifies the dead-end corridor distance to help prevent occupants from getting trapped in a corridor. Essentially, a dead-end corridor can increase the time a person is exposed to fire conditions. If an occupant leaves his room and goes in the wrong direction in a smoke-filled corridor, for example, he will have to travel to the end of the dead-end corridor, turn around when he bumps into the wall at the end, and retrace his steps to get out of the building. The dead-end corridor distance is specified in the Section X.2.5, “Arrangement of Means of Egress,” of each occupancy chapter.
The third distance is the common path of travel distance, which is “that portion of exit access that must be traversed before reaching a point where two separate and distinct paths of travel to two exits are available.” An example might be a typical hotel guest room. There is only one door out of the room and consequently one direction of travel to leave that room. When occupants get to the room door and step into the corridor, they generally can choose to turn right or left to get to two different remote exits. Therefore, the common path of travel in this example ends at the point at which the occupant steps into the corridor and has a choice of two different exits. The common path of travel rule is generally used to determine when two separate, remote egress doors are needed from a room or space. If the common path of travel is exceeded, another choice to reach an exit is needed, and another remote door from the room is required. Common path of travel is specified in the Section X.2.5 section, “Arrangement of Means of Egress,” in each occupancy chapter.
Some occupancy chapters, such as those dealing with educational and health care, specify the maximum size a room must be in square feet when a second remote means of egress is needed.
A fourth distance is specified for health care occupancies. This chapter also specifies a maximum travel distance to a smoke barrier in the Section -X.3.7, “Subdivision of Building Spaces.”
It is important to confirm that all three distances—or four for health care occupancies—comply with the Life Safety Code to ensure that the egress system provided gives the needed protection for building occupancies.
Chip Carson, P.E., is president of Carson Associates, Inc., a fire engineering and code consultancy. He is a former member of NFPA’s Board of Directors.