Insight on NFPA 92 – Standard for SMOKE CONTROL SYSTEMS
The Technical Committee on Smoke Management Systems merged NFPA 92A1 and 92B2 into a new document, Standard for Smoke Control Systems.3 This article is a brief history of NFPA 92A and NFPA 92B and an overview of the new standard.
In the Beginning
During the mid-1970s, atrium design became prevalent, and with this architectural design approach became the need to address the management of smoke in these spaces. In 1985, the NFPA standards council established two subcommittees of the Technical Committee on Air Conditioning to prepare documents to address smoke movement in buildings.
The first edition of NFPA 92A was published in 1988 as the Recommended Practice for Smoke-Control Systems. Its scope was "smoke management using smoke barriers, airflows, and pressure differences to confine smoke movement to the area of origin." In 2006, it became the Standard for Smoke-Control Systems Utilizing Barriers and Pressure Differences.
The purpose of 92A was to provide methods to:
- Inhibit the movement of smoke into stairs, means of egress, elevator shafts, and similar spaces;
- Maintain a tenable environment in refuge areas and means of egress during the time required for evacuation;
- Inhibit the migration of smoke from a smoke zone;
- Provide tenable conditions outside the smoke zone to allow emergency response operations; and,
- Contribute to protection of life and reduction in property loss.
The design objectives were presented as:
- Contain smoke to the zone of origin;
- Maintain a tenable environment in stairs;
- Maintain tenable egress to reach a refuge area or exit from a building; and,
- Other performance-based objectives to meet approval of the authority having jurisdiction (AHJ).
The standard offered five basic design approaches to achieve the purpose and objectives:
- Stairwell pressurization;
- Zoned smoke control;
- Elevator smoke control;
- Vestibules; and,
- Smoke refuge areas.
The standard provided requirements related to building equipment and controls, smoke control system design documentation, and system testing. Annex materials offered examples of stairwell pressurization system design, types of HVAC systems, fire fighters' smoke control station (FSCS) considerations, advisory information on system acceptance testing, and information reference material.
The first edition of NFPA 92B was published in 1991 as the Guide for Smoke Management Systems in Malls, Atria, and Large Areas. Its scope was to "provide methodologies for estimating the location of smoke within large-volume space or in an adjacent space." In 2005, it became the Standard for Smoke Management Systems in Malls, Atria, and Large Areas.
The purpose of 92B was to either:
Maintain a tenable environment in large volume spaces or Control and reduce the migration of smoke between the fire area and adjacent spaces
The design fundamentals presented addressed:
- Objectives of the design (maintain a tenable environment or maintain a smoke layer interface);
- Design basis (fire to be used, dimensions of the volume to be protected, communicating spaces; occupancy uses and location, barriers separating the space, egress routes, and refuge areas);
- Approaches (combinations of natural smoke filling and mechanical exhaust to predetermined level for a specified time or indefinite period);
- Considerations of the design;
- Smoke management system operation; and,
- Make-up air
The standard also addressed calculation procedures to be followed, algebraic equations, requirements for equipment and controls, system acceptance testing, and design documentation to be provided. The Annex of 92B provided explanatory material, methods for predicting the rate of heat release of fires, explanation and use of t-squared fires, example problems demonstrating the use of the equations in NFPA 92B, zone and CFD fire models, additional design objectives, considerations regarding smoke stratification, comparison of the equations presented, and informational references.
Introducing the New NFPA 92
In the creation of the NFPA 92, the directive to the technical committee was to blend the NFPA 92A and 92B without making technical changes to their intent. In many cases, this allowed existing wording to be carried over into the new document intact and in its previous location. In others, existing wording was retained, but located in a more appropriate location. While there were several sections that were moved as well as modified, the committee was careful not to change the intent of the requirements from the previous documents.
So, what is new with the merged NFPA 92? First will be the name. The new document's title is Standard for Smoke Control Systems. Why the name change? Smoke control captures both the concepts of "smoke management" and "smoke containment" systems.
The scope of NFPA 92 is: the design, installation, acceptance testing, operation, and ongoing periodic testing of smoke control systems.
The new standard has five stated purposes to accomplish one or more of the following:
- Inhibit smoke from entering stairwells, means of egress, smoke refuge areas, elevator shafts or similar areas;
- Maintain a tenable environment in smoke refuge areas and means of egress during the time required for evacuation;
- Inhibit the migration of smoke from the smoke zone;
- Provide conditions outside the smoke zone that enable emergency response personnel to conduct search and rescue operations and to locate and control the fire; and,
- Contribute to the protection of life and to the reduction in property loss.
The standard offers two design objectives, either to contain the smoke to the zone of origin by establishment and maintenance of pressure differences across smoke zone boundaries or to manage the smoke within a large-volume space and any unseparated spaces that communicate with the large volume space.
The basis of design of systems is covered in five approaches, one for smoke containment systems and four for smoke management systems. The smoke containment approach may be followed for:
- Stairwell pressurization;
- Zoned pressurization;
- Elevator pressurization;
- Vestibule pressurization; and,
- Smoke refuge area pressurization.
The other four approaches are for smoke management systems and include:
- Natural smoke filling and mechanical exhaust to maintain a predetermined smoke layer height;
- Mechanical exhaust to remove smoke to maintain the smoke layer for sufficient time to allow safe egress;
- Gravity venting to maintain the smoke layer at a predetermined height indefinitely or for a set time interval to allow safe egress; and,
- Opposed airflow to prevent smoke movement between large volume and communicating spaces.
Chapter 4, "design fundamentals," from the two predecessor documents have been merged into a new Chapter 4 of NFPA 92. Chapter 5 of NFPA 92A, "smoke control systems and applicability," has also been relocated to Chapter 4 of NFPA 92.
The calculation procedures of Chapter 5 of NFPA 92B are still in Chapter 5 of NFPA 92 and are supplemented with the information previously in Chapter 6 of NFPA 92B.
Chapters 6, 7, and 8 have been recast as follows:
Chapter 6 consolidates all of the "building equipment and controls" considerations into a single chapter;
Chapter 7 is now "smoke control documentation" and follows consistent design documentation, design report, and operations and maintenance requirements; and,
Chapter 8 is now "testing" and provides detailed testing, retesting, and documentation requirements for all systems covered by the new standard.
All of the previous annex material from both 92A and 92B has been retained and reorganized. As such, the document now has ten annexes.