NFPA 92: Why it matters, how to use it, and changes to anticipate in 2018

NFPA 92: Standard for Smoke Control Systems provides fire protection engineers with guidance for the design and testing of smoke control systems, and there are critical changes underway to the 2018 edition.

05/31/2017


This article is peer-reviewed.

Learning objectives:

  • Explain that NFPA 92: Standard for Smoke Control Systems is the primary standard that guides fire protection engineers.
  • How to comply with NFPA 92 to contain and manage smoke in a nonresidential building.
  • Learn about the 2018 edition of NFPA 92.

NFPA 92: Standard for Smoke Control Systems is the industry standard that designers, code enforcers, and maintenance personnel turn to when confronted with a smoke control system. NFPA 92 is referenced in the International Code Council codes, the U.S. Department of Defense’s Unified Facilities Criteria, NFPA 101: Life Safety Code, and other local codes and industry design guides. As buildings become more complex, incorporating larger and more complex open spaces, smoke control becomes even more important.

Figure 1: Smoke control includes both the containment and management of smoke. A single smoke control system can include both methodologies to protect occupants and property from the damaging effects of smoke. All graphics courtesy: JENSEN HUGHES

Recent history

In the past 5 years, NFPA 92 has evolved from two standards segregating the design of large-volume-space smoke management from the design of stairwell pressurization, zoned and elevator smoke control, vestibules, and smoke-refuge areas. In 2011, NFPA 92A Standard for Smoke-Control Systems Utilizing Barriers and Pressure Differences merged with NFPA 92B Standard for Smoke Management Systems in Malls, Atria, and Large Areas to form the current edition of NFPA 92.

The current year revision of NFPA 92 is the 2015 edition. The 2018 revision cycle has already begun, and the second draft’s public comments closed in November 2016. The second draft posting date is slated for August 2017.

Introduction to NFPA 92

As stated in the scope of the standard, NFPA 92 applies to the design, installation, acceptance testing, operation, and ongoing periodic testing of smoke control systems. How smoke is “controlled” in buildings can vary greatly and depends upon the specific traits of a facility. Therefore, NFPA 92 addresses the many means of controlling smoke, such as inhibition of smoke from entering stairwells, means of egress, smoke refuge areas, elevator shafts, or other similar areas where occupants may congregate or egress. It could also mean maintaining a tenable environment for the time required for safe evacuation, the inhibition of smoke migration by compartmentation, protecting and aiding emergency response operations, and improving life safety and reducing property loss. The design goals, methods, and criteria for smoke control systems are discussed in the next section.

NFPA 92 is a standard and not a code; therefore, designers and authorities having jurisdiction (AHJs) do not find the requirement for a smoke control system in NPFA 92. The locally adopted building code, such as the International Building Code (IBC) or NFPA 101, will require smoke control systems in certain cases and reference NFPA 92 as the governing standard for designing, installing, and testing of such systems.

Complying with NFPA 92

The term “smoke control” encompasses both the containment of smoke in a designated zone as well as the management of smoke within a large-volume space and adjacent connected spaces. NFPA 92 is structured around smoke containment and smoke management, providing approaches and criteria for the implementation of each.

Once the requirement for a smoke control system is established, the first step is to consult NFPA 92 and determine whether the system should be based on the smoke-containment concept or the smoke-management concept. Smoke management generally is used for large multistory spaces, such as atriums. Smoke containment, achieved using pressurization, is used for elevators, stairways, and zoned smoke systems. Additionally, a building may include smoke management as well as a smoke containment; the two methodologies are not mutually exclusive systems and both are often found in the same building. After the design methodology and smoke control objectives are identified, the design approach(es) should be selected.

Figure 2: The graphic illustrates the advantages and disadvantages of UUKL certification for smoke control systems. For smoke-containment systems, the design approach includes one or more of the following: stairwell pressurization, zoned smoke control, elevator pressurization, vestibule pressurization, and smoke refuge area pressurization.

Smoke-management systems apply within large-volume spaces and their respective communicating spaces. The design approaches can include one or more of the following:

  • Natural smoke filling and calculating/modeling of smoke layer descent to determine at what point occupants will be exposed if their egress inhibited.
  • Mechanical smoke-exhaust capacity to remove enough smoke to maintain the smoke layer above the height where it affects occupants’ ability to egress.
  • Mechanical-exhaust capacity to remove smoke to slow the rate of smoke layer descent for a period that allows adequate time for occupants to egress.
  • Gravity smoke venting to maintain the smoke layer interface at a predefined height for a design time.
  • Gravity smoke venting to slow the rate of smoke layer descent for a period that allows occupants to egress.
  • Opposed airflow to prevent smoke movement between a large-volume space and communicating space.

Keeping the design basis in mind, the smoke control approaches should be clearly defined and documented from the beginning. The report should also document the next step, establishing the design criteria. The criteria may apply to one or both of the smoke control methodologies and can help assess the effectiveness of a smoke control system; they can be found in Section 4.4 of NFPA 92.

Once the general design requirements are established, the next step is to perform the design calculations. A number of techniques including hand-calculation methods, scale models, or computer models can be employed at this stage. Special consideration should be given to the design fire, including likely fuel materials, location, intensity, and growth. It often helps to develop several fire scenarios to determine a conservative, yet reasonable, fire situation and ensure the smoke control system can operate effectively under a variety of circumstances. Chapter 5 of NFPA 92 outlines the calculation procedures related to smoke management. It is important to note that NFPA 92 does not provide guidance for design calculations for smoke-containment systems.

Once the calculations are completed, the design of the system can begin. Chapter 6 of NFPA 92 outlines the building equipment and controls requirements. One of the most widely recognized and discussed stipulations of this chapter is the requirement for control systems to be listed in accordance with UL 864: Standard for Control Units and Accessories for Fire Alarm Systems, which includes the UUKL listing that establishes a rating for the equipment used within a smoke control system, for their intended purpose.

After establishing the design approach, equipment layout, and controls specification, the last step of the design process involves the documentation of the system. Detailed requirements for the design report can be found in Chapter 7 of NFPA 92. Careful records of the design approach, methodology, design criteria, and other relevant information are crucial to the commissioning and acceptance-testing process of smoke control systems.

Additionally, the operations and maintenance manual should be developed, using Chapter 8 of NFPA 92 as guidance for the testing and maintenance throughout the life of the system. Compared with other systems, where the testing and maintenance is mainly prescriptive and based on code requirements or the equipment installed, the designer is obligated to be involved in the development of the testing and maintenance procedures because each smoke control system must be tested against its exact design criteria. Therefore, the designer must ensure the proper procedures are followed to test and maintain each unique smoke control system configured to a specific building by providing procedures for commissioning, testing and inspection (including required frequency), critical design assumptions and limitations, and the overall purpose of the system.


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