The previous article in this series described the means of egress system as “providing a protected path of travel from any occupied point within the building, typically through a series of egress components, then out to a public right-of-way.” As mentioned, the IBC, NFPA and IFC codebooks each list more requirements for means of egress than any other chapter, so this article is the second of two parts for this extensive subject.
Of the 30 sections in the IBC’s means-of-egress chapter, I’ve selected eight of the most significant ones to discuss. In the prior article, the means-of-egress system presented the three distinct areas of exit access, exit and exit discharge, as well as four of the eight most significant sections (Administration, General Means of Egress, Occupant Load and Means of Egress Sizing). The focus of this follow-up article is the means-of-egress components, thereby highlighting the extensive requirements and multiple chapter sections for doors, corridors, stairs and elevators.
The IBC presents the means-of-egress doors component in three sections: 1006 Number of Exits and Exit Access Doorways; 1007 Exit and Exit Access Doorway Configuration; and 1010 Doors, Gates and Turnstiles.
IBC Section 1006 Number of Exits and Exit Access Doorways
Section 1006’s most important issue is that two exits or exit access doorways from any space are required when the design occupant load or common path-of-egress travel distance exceeds the values listed in Table 1006.2.1 Spaces with One Exit or Exit Access. The general rule for most use groups is that the code requires at least one means of egress for up to 49 occupants at least two for 50 to 500 occupants. For the data centers’ typical use groups of S, B and sometimes H (storage, business and hazard), however, this rule only applies to B. Use group S requires at least one exit for up to only 29 occupants, and use groups H-1, H-2 and H-3 require at least one exit for up to only 3 occupants.
This “Spaces with One Exit or Exit Access” table also limits the maximum distance to a common path of travel. (A common path of travel commences when a path of travel has two separate means of egress.) Use groups B and S require the distance to a common path of travel to be no more than 100 feet, provided the building is sprinklered. Use groups H-1, H-2 and H-3 require the distance to a common path of travel to be no more than 25 feet, provided the building is sprinklered, and a single exit in H is prohibited (NP) without a sprinkler system.
IBC Section 1007 Exit and Exit Access Doorway Configuration
Section 1007’s most important issue is remoteness: when two exit or exit-access doors are required, they must be set at a distance of at least one-half the distance of the overall diagonal it serves (such as the diagonal of each space, room, fire-control area and building). If the building is fully sprinklered, the minimum distance can drop to at least one-third of the overall diagonal. Where three exit or exit-access doors are required, not less than two shall meet the overall diagonal requirements, and the remaining required ones shall be set at “a reasonable distance apart.”
IBC Section 1010 Doors, Gates and Turnstiles
The most important issues regarding swinging doors are the following. They must be minimum 32 inches wide (with the door opened at 90 degrees, it’s measured from face of door to the face of the door stop), the leaf shall not be more than 48 inches wide, projections into the clear width are not allowed lower than 34-inches above the floor, door closers must be set a minimum of 78 inches above the floor, and except for door closers, projections into the clear width between 34 and 80 inches above the floor shall not be greater than 4 inches.
The most important issues regarding revolving doors are that they “shall be capable of breakout (where each door leaf can be forced into a hinged-style operation)…and provide a width of not less than 36-inches,” they “shall not be located within 10 feet of the foot or top of stairways,” each revolving door “shall have a side hinged door…in the same wall and within 10 feet of the revolving door,” revolving doors shall not be part of an accessible route, and “revolving doors shall not be given credit for more than 50 percent of the minimum width or required capacity.”
In addition to the above, Section 1010 also includes a host of other issues, such as the following:
- A landing at a door shall have a width of at least the width of the door or the stairway it serves, and landings are required on both sides of a passage door (1010.1.6).
- Thresholds may not exceed 1/2 inch above the finished floor and must be beveled if greater than 1/4 inch (1010.1.7).
- The distance between two swing doors in a series must be at least 48 inches beyond the edge of 90-degree open door swinging into the space, and the distance between two automatic horizontal sliding doors in a series must be at least 48 inches (1010.1.8).
- Door handles, pulls, latches, locks and so on must be set between 34 inches minimum and 48 inches maximum (1010.1.9).
- Manually operated bolts (flush, edge or surface mounted) are prohibited on single passage doors, but they’re allowed on a double door’s inactive leaf in use groups S or B, provided the building is fully sprinklered and the occupancy load is less than 50 or the active leaf meets the occupancy requirements (1010.1.9.4).
- Delayed egress-locking devices are allowed in use groups S and B but not H or A (assembly) provided the delayed lock is deactivated under certain conditions (by the building’s sprinkler system, by an approved automatic smoke and heat detection system, by the loss of power or “at the fire command center and other approved locations”) and several other requirements are met (1010.1.9.7).
- Stairway doors that serve as a means of egress “shall be openable from both sides without the use of a key or special knowledge or effort.” But one of the five exceptions allows stairway discharge doors to be locked on the side opposite the egress side (1010.1.9.11).
- Panic devices and fire exit hardware are only required in use groups H, A and E (education) with occupancies of 50 or more persons, and in electric rooms over 6 feet wide that have 1,200 amperes, overcurrent devices and exit doors. Since most data centers are in use groups S, B and sometimes H, most don’t require panic bars or push-pads on any doors except for their electric rooms (1010.1.10).
The IBC has means-of-egress corridors primarily addressed in a specific chapter section (1020), but it also touches on corridor requirements in other sections of the chapter (1008 and 1017).
IBC Section 1020 Corridors
- As a general rule, corridors must typically be sprinklered and/or fire rated. The specifics appear in Table 1020.1, which determines fire ratings and sprinkler requirements as they pertain to each use group. Five exceptions are listed, but the two that apply to data centers are (1) in use group B, where rated corridors aren’t required if only a single egress is required, and (2) corridors adjacent to the exterior walls of a building can have unprotected openings on unrated exterior walls (1020.1).
- A corridor’s minimum width and capacity appears in Table 1020.3, which typically requires 44 inches minimum, but 36 inches is allowed for rooms or spaces up to 49 occupants, and 24 inches is allowed for access to mechanical, electrical and plumbing equipment spaces (1020.2).
- Dead-end corridors are typically required to have a length not exceeding 20 feet, with two exceptions applicable to data centers: (1) dead-end corridors shall not exceed 50 feet as long as the building is fully sprinklered, and (2) dead-end corridors shall not be limited in length if the corridor’s width is at least 2.5 times its length. This rule recognizes that an occupant is less likely to be trapped in wide-proportioned area than in a long narrow one (1020.4).
- Apart from four exceptions, corridors shall typically not “serve as supply, return, exhaust, relief or ventilation air ducts” (1020.5), but the space above the corridor ceiling may, under certain conditions, be used as a return air plenum (1020.5.1).
- Corridors shall have continuity, to where “fire-resistance-rated corridors shall be continuous from the point of entry to an exit, and shall not be interrupted by intervening rooms” (1020.6).
IBC Section 1008 Means of Egress Illumination
Means of Egress Illumination says, (1) “The means of egress serving a room or space shall be illuminated at all times that the room or space is occupied,” and (2) “In the event of power supply failure in rooms and spaces that require two or more means of egress, an emergency electrical system shall automatically illuminate…aisles, corridors, exit access stairways and ramps.”
IBC Section 1017 Exit Access Travel Distance
The basic concept of Section 1017 is that exit access shall be as listed in Table 1017, which provides the occupancies and their maximum travel distance to an exit with and without a sprinkler system. The most important issues in the table regarding data center’s typical groups of S, B and sometimes H are the following:
- Use group S-1 allows up to a 200-foot exit-access travel distance without sprinklers and 250 feet if sprinklered.
- Use group S-2 allows up to a 300-foot exit-access travel distance without sprinklers and 400 feet if sprinklered.
- Use group B allows up to a 200-foot exit-access travel distance without sprinklers and 300 feet if sprinklered.
- Use groups H (H-1 through H-5) allow exit-access travel distance ranges of 75 to 200 feet with a sprinkler system, and group H is not permitted (NP) without a sprinkler system.
IBC Section 1011 Stairways presents the requirements for each basic element (indicating, among other things, that a degree of safety may come from maintaining consistency in dimensions):
- The typical minimum required width shall be the greater of either the required egress capacity per Section 1005 (as described in the previous article) or no less than 44 inches, with the exception that 36 inches is allowed if serving under 50 occupants.
- Headroom shall be no less than 80 inches above the landing or above a stair tread’s nosing.
- The stair risers’ height shall be 4 inches minimum and 7 inches maximum, the treads’ depth shall be 11 inches minimum, and the variations in a step’s depth or height shall not exceed 3/8 inch in any flight.
- A tread’s nosing shall have a curvature or bevel between 1/16 and 9/16 inch, its projection shall not exceed 30 degrees from the vertical and it shall not project more than 1-1/4 inch beyond the tread below.
- Stairway landings are required at the top and bottom of each flight, and the width shall not be less than that of the stairs it serves (except in a stairs with a straight run, the landing doesn’t have to be wider than 48 inches). Also, doors that open over the landing may not encroach into the landing more than 7 inches when the door is fully open, and the door swing’s arc shall not reduce the landing’s width to less than half of its requirement. Plus, if a wheelchair space is required on the landing (to meet the requirements for area of refuge), the door may not swing into the area set aside for it.
- In a building that’s four stories or more above the grade plane and whose roof is no steeper than a 4:12 pitch, a permanent set of stairs shall extend to the roof. If the roof is unoccupied, the stairs can be in the form of “an alternating tread device, ships ladder, or permanent ladder.”
- Per IBC Section 1009.1, accessible (ADA) spaces in new construction must have at least one accessible means of egress (or at least two as required per Sections 1006.2 or 1006.3). Per Section 1009.3 (and apart from nine exceptions), stairways between stories may serve as an accessible means of egress, provided they “have a clear width of 48 inches minimum between handrails and shall either incorporate an area of refuge within an enlarged floor-level landing or shall be accessed from an area of refuge complying with Section 1009.6. Exit access stairways that connect levels in the same story are not permitted as part of an accessible means of egress.”
Elevators are not to be considered as part of a means-of-egress system, but per IBC Section 1009.1, accessible spaces in new construction must have at least one accessible means of egress (or at least two as required per Sections 1006.2 or 1006.3). So to help meet this requirement, Section 1009.4 relays that elevators may be considered part of an accessible means of egress under the following conditions:
- They “…shall comply with the emergency operation and signaling device requirements of Sections 2.27 of ASME A17.1.”
- Their “standby power shall be provided in accordance with Chapter 27 and Section 3003.”
- Apart from five exceptions, the elevator “shall be accessed from an area of refuge complying with Section 1009.6.”
The means-of-egress system (exit access, exit and exit discharge), as expected, is mutually dependent on its means-of-egress components (doors, corridors, stairs and elevators). Like a chain comprising individual links, each of the extensive means-of-egress code requirements and multiple chapter sections combine to establish at least one safe evacuation pathway from any occupied place in a building out to the safety of a public right-of-way.
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.