NFPA 92 defines design, testing of smoke control systems
Smoke management systems
Several criteria specified in Chapter 4 are written to apply exclusively to smoke management systems. Example requirements include a minimum smoke layer depth (20% of floor to ceiling height or based on engineering analysis) and a maximum make-up air velocity (200 ft/min near plume or based on engineering analysis). Most smoke management system designs are required by Section 4.5 to be based on tenability and egress analyses; however, these analyses are outside the scope of NFPA 92. In the current revision cycle, consideration has been given to creating a new Annex to address tenability.
Section 18.104.22.168 requires an egress analysis to be conducted when the smoke management system design objectives include maintaining tenability for the time necessary for occupants to exit the building or preventing occupants from being exposed to smoke. This requirement applies to the majority of smoke management system designs, as three of the four possible design objectives contained in Section 4.1.2 fit this description. Section 22.214.171.124 also requires that these systems remain operational for the calculated duration of egress. This requirement coincides with that of section 4.2.3, which together require that equipment must be capable of operating under exposure to the anticipated elevated temperatures for the calculated duration of egress.
Section 126.96.36.199 states that systems designed in accordance with objectives 2 or 3 from Section 4.1.2, which involve maintaining tenability for the duration of egress, are permitted to use design approach 3 or 5 from Section 4.3.2, which involve controlling the rate of smoke layer descent. Section 188.8.131.52 permits flexibility in the design in that occupants are permitted to be exposed to smoke, so long as conditions remain tenable for the duration of egress.
Chapters 5 through 8
Chapter 5 contains calculation procedures for smoke management system designs. Section 5.1 specifies three different methods that can be used for the design of a smoke management system:
- Algebraic equations (see the remainder of Chapter 5)
- Scale modeling (not very common)
- Compartment fire models (includes zone fire models such as consolidated model of fire and smoke transport (CFAST) and computational fluid dynamics (CFD) models such as fire dynamics simulator (FDS)).
NFPA 92 does not contain calculation procedures for smoke containment systems. The SFPE Handbook of Fire Protection Engineering and ASHRAE/ICC/NFPA/SFPE Handbook of Smoke Control Engineering are two commonly used resources for calculation procedures regarding these systems. These handbooks also contain additional information regarding smoke management system design.
Chapter 6 contains requirements regarding equipment and controls that are used as part of, or may affect the operation of, the smoke control system, such as HVAC controllers, firefighters’ smoke control stations, smoke detectors, or dampers. Chapter 7 contains requirements regarding the two documents required to be generated during the design process, the Detailed Design Report and the Operations and Maintenance Manual. Chapter 8 contains smoke control system testing requirements.
As noted earlier, the annexes are included for informational purposes only, and are not part of the requirements of NFPA 92.Information in the 13 annexes includes additional calculation procedures and examples, assistance with choosing a design fire and associated heat release rate, and additional information regarding CFD and zone modeling, HVAC air-handling and stairwell pressurization system types (compensation types), and testing.
Upcoming NFPA 92 changes
NFPA 92 currently is being revised as part of the fall 2014 NFPA code cycle. NFPA is still accepting public comments on the first draft report (visit www.nfpa.org/92 for information about the next edition or to submit a notice of intent to make a motion); therefore, nothing has been set in stone. Nevertheless, it is certain that the 2015 edition will feature several editorial revisions and minor revisions to comply with the NFPA Manual of Style and clarify the intent of the standard.
For example, Section 184.108.40.206 is slated to be reworded to clarify that smoke control system operational capability does not have to be verified by weekly tests; rather, it can be verified by other means such as electrical monitoring (supervision) of the control equipment. The committee also has proposed to incorporate references to the 2015 edition of NFPA 4: Standard for Integrated Fire Protection and Life Safety System Testing. In the 2015 edition of NFPA 92, tenability threshold guidance may potentially be brought over from NFPA 130: Standard for Fixed Guideway Transit and Passenger Rail Systems for incorporation into Annex D.
One of the only major changes that has been proposed and is currently under consideration is a substantial revision of the balcony spill equations contained in Chapter 5 (Section 5.5.2). New correlations have been proposed as a result of significant research in the area by Roger Harrison at the University of Canterbury, New Zealand. These new correlations have the potential to yield more accurate calculations and cover a wider range of scenarios than the existing correlations.
William E. Koffel is president of Koffel Associates and is a member of the NFPA Technical Committee on Smoke Management Systems. Nicholas Sealover is a fire protection engineer with Koffel Associates.