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#101Wednesdays – What is Smoke Control and Do I Need it?

Blog Post created by jsisco Employee on Apr 17, 2019

Photo Courtesy of Andysmith248 [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

 

As a staff engineer I often get the question through our technical question service (TQS) if a smoke control system is required. Although there are a few times where NFPA 101®  prescribes the use of a smoke control system, for the most part it is a choice by the building designer to comply with performance criteria in the Code.

Smoke control is an engineered system that is designed to modify the movement of smoke. Where the NFPA 101 requires a smoke control system, it is required to comply with NFPA 92, Standard for Smoke Control Systems. There are two main types of smoke control systems per NFPA 92: smoke containment systems and smoke management systems. The purpose of smoke containment system is contain smoke to a given area and prevent it from entering another area, such as with a stairwell pressurization system. The purpose smoke management system is maintain tenability of an area or means of egress and reduce migration of smoke between the fire area and adjacent spaces, such as with an atrium smoke control system.

There are several times in which NFPA 101 prescribes the use of smoke control:

  1. New underground buildings or portions of buildings that have an occupant load greater than 100 persons underground, has a human occupied level more than 30 ft. or more than one level below the lowest level of exist discharge, and has combustible contents, interior finish or construction, is required to be provided with an automatic smoke venting.
  2. The second is for levels in new assembly occupancies 30 ft. or more below the lowest level of exit discharge which are required to be divided into two smoke compartments, each provided with its own independent smoke control or smoke exhaust system.
  3. Enclosed mall concourses connecting more than two stories.

There are other times that a smoke control system may be required in order to meet a performance criterion. Such as new atria which require an engineering analysis to demonstrate that the smoke layer interface is maintained above the highest opening or at least 6 ft. above the highest floor level for a time period of 1.5 times the calculated egress time or at least 20 minutes. An atrium may be able to achieve this performance criteria without the use of a smoke control system, however, for some buildings the installation of a smoke control system may be necessary to achieve a desired atrium design.

 

Stairwell pressurization systems as a means to provide a smokeproof enclosure is another common example of smoke control systems. Smokeproof enclosures are required to be designed to limit the movement of smoke, this is permitted to be achieved through natural ventilation, mechanical ventilation incorporating a vestibule, or by enclosure pressurization.

 

In addition to atria and smokeproof enclosures, smoke control systems may be utilized to meet a design criterion for buildings and designs including underground and limited access buildings, smoke-protected assembly seating, stages in assembly occupancies, detention and correctional occupancies, mall concourses, as part of an engineered life safety system, or in performance-based designs in accordance with Chapter 5.

 

For most buildings and designs, with the exception of underground buildings and mall concourses, the Code will not prescribe the use of a smoke control system. However, based on the use and design of the building, the use of a smoke control system may be desired or necessary to meet the prescribed performance criteria in the Code.

 

Did you know NFPA 101 is available to review online for free? Head over to www.nfpa.org/101 and click on “Free access." 

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