Engineering considerations of NFPA 101
NFPA 101: Life Safety Code defines a building’s egress, along with numerous fire and life safety systems.
NFPA 101: Life Safety Code (LSC) addresses issues such as the number of means of egress, the arrangement of the means of egress, the capacity of the means of egress, egress components, and interior finish. Because of this, some think of the code as a document that addresses only the architectural features of these components of a building. However, NFPA 101 contains numerous requirements that need to be addressed by engineers who are part of the design team, such as fire/smoke barriers that may have an impact on system designs, the need to protect openings and penetrations, and fire protection systems. This article will focus on the engineering aspects of NFPA 101, common misapplications, and examples of where NFPA 101 and the International Building Code (IBC) differ or overlap.
Organization, application of NFPA 101
For those not familiar with the code, it is necessary to understand that the organization of NFPA 101 is occupancy-based. There are core chapters in the document (Chapters 1-10) that either establish the minimum criteria for most occupancies or provide a menu of options from which the design team may choose (such as the protection of vertical openings) based on the requirements of the occupancy chapters. Once the user of the document knows the occupancy classification of the area being considered and whether the issue being considered is defined as new or existing, he or she should go to the appropriate occupancy chapter for that application. Note that most occupancies have separate chapters for new and existing conditions.
This leads us to LSC common mistake No. 1: The provisions in the chapters dedicated to existing buildings apply to existing conditions—those in existence at the time the edition of the code was adopted. Any new work and changes to an existing system are to be done in accordance with the requirements for new construction unless the work is specific to correcting a deficiency. Work that is required to bring an existing building into compliance with the code need only meet the requirements established in the existing occupancy chapter. Chapter 43, Building Rehabilitation, of the 2012 LSC contains the requirements regarding any new work in an existing building.
For example, if an existing audible alarm notification appliance is not working, the device may be replaced with one that is the same as the existing device even if current audibility criteria are not met. (This is defined as a repair project.) If the decision is made to replace the occupant notification portion of a fire alarm system, the project is considered a renovation project and one could replace device for device, again without necessarily meeting all the requirements, for a new system. While it may be a good opportunity to upgrade the existing system, the code would not necessarily require that this be done unless an imminent hazard exists by not complying with the newer criteria. If occupant notification is being added to a building as a new feature, the project is considered a modification project, and now the requirements for new construction must be met. Whatever is being done, the work must at least meet the requirements for existing.
In addition, an existing life safety feature may not be reduced unless it exceeds that which is required for new construction. For example, assume that a fire alarm system transmits an alarm to a supervising station and that feature is required for new construction, but not for an existing building. Even if the building is an existing building, the supervising service must be retained since it is required for new construction.
This leads us to LSC common mistake No. 2: Quite often someone wants to apply the requirements of the occupancy chapter that applies to existing buildings to say that the existing condition or feature need not be continued because it is not required for existing buildings without determining if it is required for new construction.
Protecting exit enclosures
The code prohibits openings into exit enclosures other than those from normally occupied areas, those from corridors, and those necessary to egress from the exit enclosure. As such, doors from mechanical and electrical equipment rooms are not permitted to open directly into the enclosure. Access panels to adjacent utility shafts are not permitted in the barriers separating the exit enclosure from the shaft. In addition, penetrations into the exit enclosure are restricted to those necessary for services within the exit enclosure. Therefore, other than the sprinkler system riser, the exit enclosure shall not be used as a shaft for building systems.
While protection of vertical exit stairs may be well understood, at times the egress design will also include horizontal exit enclosures, referred to as exit passageways.
LSC common mistake No. 3: For the most part, the same restrictions and rated construction that apply to exit stairs also apply to exit passageways. This limitation is often overlooked because on the drawings, an exit passageway may appear to be the same as a corridor other than the fire barriers may have a higher fire resistance rating and have no openings other than the entrances to the exit enclosure, doors from normally occupied spaces, and the door opening to the outside/public way.
Emergency lighting and standby power
With respect to emergency lighting, the code contains a specific requirement that when emergency lights are required, they shall operate whenever a single failure can result in the area being in darkness. This includes loss of the primary power source to the building, as well as the tripping of a circuit breaker on a lighting circuit or operating a switch. This is usually accomplished by designing the lighting circuits in an area such that a single act will not result in the loss of all lights, other than the loss of the primary power source. Where provided, battery operated emergency light units must be tied into the lighting circuit and not any other circuit that might be more convenient from a wiring perspective. Emergency generators are often used as the source of standby power as well.
New to the 2012 edition of NFPA 101, the pressure maintenance pump and air compressors for dry pipe and pre-action sprinkler systems are required to be connected to a standby power supply in high-rise buildings other than special-purpose industrial occupancies. It is important to note that, in addition to being a new requirement, this provision may be more restrictive than some of the other applicable codes for the project.
HVAC and smoke control systems
There are numerous differences between the requirements for HVAC systems in NFPA 101 as compared to some other codes that might apply to the project. The reference standard in NFPA 101 is NFPA 90A: Standard for the Installation of Air Conditioning and Ventilating Systems, which provides the requirements for dampers and automatic controls for the HVAC system. One example of a difference between applicable codes is the IBC requirement for smoke dampers at duct penetrations of rated shaft enclosures, which is not found in either NFPA 101 or NFPA 90A. There are also some differences as to when the HVAC system is required to shut down upon detection of smoke in the supply or return air. NFPA 101 does require standby power for HVAC smoke control equipment in high-rise buildings, which corresponds to the IBC requirements.
While NFPA 101 addresses smokeproof enclosures and one type of smokeproof enclosure is a pressurized stair, the code rarely requires smokeproof enclosures, even in high-rise buildings. When a pressurized stair is provided, the design criteria may be different than found in other codes, in part due to the differences in how many doors are assumed to be open. The IBC establishes a minimum pressure difference with all stairway doors closed. However, NFPA 101 requires that the designer determine with the authority having jurisdiction (AHJ) and local codes how many doors may be open at any given time, and then determine the pressure difference based on the number of doors that may be in the open position. Section 7.2.3 of NFPA 101-2012 establishes the requirements of smokeproof enclosures when required under other provisions of the code, and Section 22.214.171.124 describes the requirements for enclosure pressurization. It is prudent for the designer to compare the LSC with the IBC requirements and the AHJ requirements.
In addition to addressing features that are commonly addressed by an architect, NFPA 101 contains numerous requirements that need to be addressed by the design team engineers. Some of the requirements are related to maintaining the integrity of a building feature (e.g., fire barrier), and some are criteria for the building fire and life safety systems.
William E. Koffel is president of Koffel Associates. He is chair of the NFPA Correlating Committee on Life Safety and a member of numerous NFPA technical committees. He is a member of the Consulting-Specifying Engineer editorial advisory board.