One Way Out
Determining the number of means of egress
NFPA Journal®, March/April 2012
Not every building or area needs two ways out. Think of a phone booth (if you can recall such things): it has four walls and a roof, which is pretty much the definition of a building. But a phone booth has only one way out and it seems perfectly okay. How much bigger than a phone booth can a building get before it requires two ways out? NFPA 101®, Life Safety Code®, clearly tells us in the “Number of Means of Egress” section of each occupancy chapter.
This question of number of means of egress often arises in small industrial and storage buildings. Can a small maintenance shop, manufacturing building, or storage building have a single exit? The answer is a qualified “yes.”
Section 40.2.4, “Industrial Occupancy,” states that not less than two means of egress are to be provided on each story and not less than one exit must be reached without traversing another story. What that tells us is there must be at least one exit — a door to the exterior, an enclosed exit stair, a horizontal exit, or an exit passageway — directly available from each floor. The second means of egress could be an open stair to another floor. Remember, industrial plants often have multiple work platforms that are not necessarily stories. A story is defined as “the portion of a building located between the upper surface of a floor and the upper surface of the floor or roof next above.”
Section 188.8.131.52.2 goes on to state that a single exit is permitted from any story or section where the exit can be reached within the permitted common path of travel and the building cannot be classified as high-hazard as defined in Section 184.108.40.206. The common path of travel is the distance one must cover before reaching a point at which a choice is available to two separate and remote exits. The common path of travel for any occupancy is always found in the _.2.5 section of the appropriate occupancy chapter. The common path of travel for general industrial occupancies, assuming ordinary hazard, is 50 feet (15 meters) without sprinklers and 100 feet (30 meters) with sprinklers. So a one-story machine shop protected by sprinklers could have a single exit door if the distance from the most remote occupiable portion of the building to the exit door, measured as one would actually walk, does not exceed 100 feet (30 meters).
The storage occupancy chapter has a similar requirement. Section 220.127.116.11(2) states that, in ordinary hazard storage, a single means of egress is permitted from any story or section where the exit can be reached within the permitted common path of travel. Again, the common path of travel is located in the _.2.5 section and is 100 feet (30 meters) with sprinklers and 50 feet (15 meters) without sprinklers.
If the industrial occupancy is considered high-hazard, as defined in Section 18.104.22.168, then Section 7.11, “Special Provisions for Occupancies with High-Hazard Contents,” applies. This section requires two exits from high-hazard spaces unless the space is no larger than 200 square feet (18.6 square meters), has an occupant load of no more than three people, and has a travel distance to the room door no longer than 25 feet (7,620 millimeters).
Industrial and storage occupancies are just two occupancies in which a single exit is permitted. Others include business, mercantile, and certain residential occupancies. This information is always located in the _.2.4 section, “Number of Means of Egress,” of the occupancy chapter.
Chip Carson, P.E., is president of Carson Associates, Inc., a fire engineering and code consultancy.