As the first article in this series introduced, the most critical aspect in a mission-critical data center is the life-safety measures it employs. The four standard systems that facilitate safe evacuation and survival during a fire are fire suppression, means of egress, fire containment and fire alarms—and I still rank means of egress as the second most important of the group. The 2015 International Building Code (IBC), the 2015 NFPA 101 Life Safety Code (NFPA) and the 2015 International Fire Code (IFC) also reinforce its importance. Each not only devotes a full chapter to means-of-egress requirements (IBC’s Chapter 10, NFPA’s Chapter 7 and IFC’s Chapter 10), but with its ample chapter requirements listed in a plethora of sections (30, 14 and 30, respectively), the means-of-egress system is each code’s largest and most extensive chapter.
The Big Picture: Basic Means-of-Egress System
The basic concept of the means-of-egress system is to provide a protected travel path from any occupied point in the building, typically through a series of egress components, out to a public way. The IBC, NFPA and IFC each separate this protected travel path into three distinct areas: exit access, exit and exit discharge.
- Exit access: According to the definitions in the IBC’s Chapter 2, exit access is “[t]hat portion of a means of egress system that leads from any occupied portion of a building or structure to an exit.” (The IFC’s definition is identical to the IBC’s, and the NFPA’s is similar but abridged.) Exit-access components include rooms being exited, exit-passage doorways (such as between a room and an egress corridor), exit passageways (egress corridors), exit-access ramps and exit-access stairs, with each component acting as portion of the exit-access system. But the exit-access requirements apply to all “occupied” rooms, areas and spaces and must (eventually) lead to an “exit.” So, uninhabited attics and crawlspaces, as well as corridors that neither directly nor indirectly lead to an exterior exit door, aren’t considered part of the required exit-access system.
- Exit: The IBC defines the term exit as “[t]hat portion of a means of egress system between the exit access and the exit discharge or public way.” Exit components include exterior exit doors at the following places: “the level of exit discharge (ground level), interior exit stairways and ramps, exit passageways, exterior exit stairways and ramps and horizontal exits.” (While the IFC’s definition is identical to the IBC’s, the NFPA’s definition adds the all-important fire-resistance concepts of being “separated from all other spaces of the building” and “to provide a protected way of travel,” but it doesn’t spell out the exit components.) In a word, the “exit” is any protected area with a passage door, or the passage door itself, that goes directly out of the building into the exit discharge or public way.
- Exit discharge: The IBC defines the exit discharge as “[t]hat portion of a means of egress system between the termination of an exit and a public way.” (The NFPA and IFC also use this exact definition.) In a word, the “exit discharge” is the path from any exterior exit door that goes directly to a public way. The public way, according to IBC’s definitions chapter, is a “street, alley or other parcel of land open to the outside air leading to a street that has been deeded, dedicated or otherwise permanently appropriated to the public for public use and which has a clear width and height of not less than 10 feet.” The main issue here is that the “exit discharge” must not only lead from the building’s exit, but it must also enable the occupants to get to an open, fresh-air public way (where they can be found by those searching for them, get medical treatment or transport if needed, or evacuate the grounds completely).
The Small Details: Means-of-Egress Requirements
The two codes that govern many jurisdictions are the IBC and NFPA 101 Life Safety, but the IBC requires observance of some codes in the IFC. Of the 30 sections in the IBC’s means-of-egress chapter, I selected four of the eight most important ones (describing the means-of-egress system) to discuss herein: Section 1001 Administration, Section 1003 General Means of Egress, Section 1004 Occupant Load and Section 1005 Means of Egress Sizing. A future article will address the extensive requirements and multiple chapter sections for the other four most important sections (describing the means of egress components such as doors, corridors, stairs and elevators).
(The IFC is similar to the IBC in that it not only has similar sections of Administration, General Means of Egress, Occupant Load and so on, but it even has the same opening statement in the Administration section. The NFPA has similar contents but places them under different headings. But wherever these three codes differ, the more stringent requirements must be applied.)
IBC Section 1001 Administration
Three important notes in the means of egress chapter appear as warnings: Section 1001.2 says that “it shall be unlawful to alter a building or structure in a manner that will reduce the number of exits or the width or required capacity of the means of egress to less than is required by this code.” Section 1001.3 requires that the means of egress shall be maintained per the IFC. Section 1001.4 requires that all buildings and all occupancies shall have a fire safety and evacuation plan. Although these warnings must be observed, the “it shall be unlawful” statement (which is also in the IFC) is interesting in that any code, by itself, cannot actually create or declare any laws—but a governing legislature can and does so whenever it officially votes to adopt a code as part of its laws.
IBC Section 1003 General Means of Egress
Section 1003 opens by saying that “the general requirements specified in Sections 1003 through 1015 shall apply to all three elements of the means of egress system”; it further mentions that they are “in addition to those specific requirements for the exit access, the exit, and the exit discharge.” It doesn’t, however, explain “all three elements” of the means of egress system in this chapter, instead mostly leaving it up to readers to realize that they should consult IBC’s Chapter 2 definitions.
Nevertheless, Section 1003 does include several general means-of-egress requirements:
- Minimum ceiling height shall be at least 7 feet 6 inches above the finish floor as a rule, but it allows exceptions for sloped ceilings, some projections, stair headroom, door height, ramp headroom, areas below a mezzanine and so on.
- Protruding objects are “permitted to extend below the minimum ceiling height…where a minimum of 80 inches is provided over any walking surface,” but it says “a barrier shall be provided where the vertical clearance is less than 80 inches high” and, further, “objects with leading edges more than 27 inches and not more than 80 inches above the floor shall not project horizontally more than 4 inches into the circulation path.”
- Floor surface(s) as part of a means of egress “shall have a slip-resistance surface and be securely attached.” Although it’s a stated code requirement, it doesn’t define any slip-resistance parameters (such as required coefficients of friction when wet or when dry). It also doesn’t consider the user’s footwear (in that some new hard-soled dress shoes or new hard-rubber work boots seem to slip on everything, possibly rendering almost every flooring as being in violation).
- Elevation changes in the means of egress that are less than 12 inches require sloped surfaces, and where the slope surface is greater than 1:20 an accessible ramp shall be used, with exceptions for places that aren’t required to be accessible.
- Elevators, escalators and moving walks “shall not be used as a component of a required means of egress,” with the exception that “elevators can be used as an accessible means of egress.”
IBC Section 1004 Occupant Load
The short IBC Section 1004 (1004.1 through 1004.6) comes with a long table (Table 1004.1.2). Sections 1004.1 through 1004.6 nonetheless do have noteworthy requirements: occupant loads are cumulative as occupants collect from additional areas along the means-of-egress path, occupant loads must be posted in an “assembly” occupancy, outdoor areas also require a means-of-egress path and so on. But the biggest takeaway of this section is that the code has established parameters that define how many occupants must be evacuated in any individual room, in each fire control area and for the total building.
The counts based on neither the number of occupants desired, how many are anticipated to arrive or actually do arrive, nor how many can actually fit into a room, area or building—it’s determined only on the basis of a “function of the space” plus the function’s “occupant load factor,” as specifically listed in Table 1004.1.2. For example, for a 5,000-square-foot space used for offices, one selects the table’s function of the space as “business,” which has a corresponding occupant load factor of 100 gross square feet per person. This number establishes that up to 50 people can occupy that room (5,000 square feet / 100 square feet per occupant). The design must enable these 50 people to safely evacuate the room by having at least two remote exit or exit-access doors (required for rooms with 50 to 500 occupants). These 50 people (along with people evacuating the other nearby rooms) must then be able to safely evacuate the building through code-compliant spaces (with fire ratings, sprinklers, illumination, exit signs, minimum door and corridor width, maximum length of travel and dead ends, and so on as required) that exit to a public way.
With a data center’s typical use-group occupancies being Storage, Business, and sometimes Hazard, Table 1004.1.2’s twenty-seven different functions have only two that pertain to a typical data center: accessory-storage areas/mechanical-equipment rooms, which have a corresponding occupant load factor of 300 gross square feet per person, and business areas, which (as already mentioned) have a corresponding occupant load factor of 100 gross square feet per person. The Hazard use group is rare, since it’s typically avoided owing to extensive requirements, but unless it falls into Group H-5’s fabrication and manufacturing, any H designation’s occupant load should be assessed as Group S, which is at 300 gross square feet per person. Locker rooms are also rare (even though I’ve seen more data centers with locker rooms than with high-hazard areas), and they come in at a high occupancy count of 50 gross square feet per person.
IBC Section 1005 Means-of-Egress Sizing
IBC Section 1005 is primarily about determining the minimum required width of a means-of-egress component. It does so by establishing “means of egress capacity factors” that will be applied to the occupant loads throughout a building (starting from each individual room, exiting through the doors, accumulating in the corridors and stairs, and exiting through the multiple exits).
The minimum width in the calculation to determine egress capacity is 0.3 inches per occupant for means-of-egress stairs, and 0.2 inches per occupant for every means-of-egress component other than egress stairs, but it “shall not be less than that specified for such component, elsewhere in this code.” So, a room with 10 occupants may have a minimum door clear opening width of 2 inches for the egress sizing (10 occupants x 0.2" per occupant), but its minimum width is actually 32 inches clear owing to the code’s accessibility requirements.
A stair’s minimum width is 48 inches (per Section 1009.3), but the minimum width of a single stair (at 0.3 inch for the egress sizing) for, say, 400 occupants on the floor with two sets of stairs must be a minimum of 60 inches (400 occupants / 2 stairs x 0.3" per occupant). It’s important to note, however, that unlike egress corridors, the capacity of the occupants in egress stairs does not accumulate along the route, so the totals for stairs are for each floor only—they don’t amass from floor to floor (1005.3.1).
Because the basic concept of the means-of-egress system provides a safe path of travel, the IBC’s, NFPA’s and IFC’s heavy emphasis (through an abundance of code requirements) plainly reinforces its importance. With that in mind, of the four standard systems that facilitate safe evacuation and survival during a fire, such an emphasis just might make the means-of-egress system the most underrated of the group.
Leading article image courtesy of DVA Architects
About the Author
Dean Ventola, RA, NCARB, LEED AP BD+C, is the Director of Construction Administration at DVA Architects in Gaithersburg, MD, a nationally prominent mission-critical data center architect.