Smoke Control

Smoke Control


Consulting and design of atrium smoke control, smoke-protected seating, zoned smoke control, high-rise, and stairwell/elevator pressurization systems.


In accordance with Section 404 of the IBC, and other standards such as NFPA 101, Life Safety Code, most atria exceeding either two or three stories require an atrium smoke control system installed in accordance with Section 909.  The common approach with these systems is to utilize the exhaust method (909.8), in which mechanical exhaust is provided at upper elevations of the atrium, and natural and/or mechanical makeup air is provided at lower elevations.  Sizing of these systems is referenced by the IBC to be designed in accordance with NFPA 92, Standard for Smoke Control Systems.  This standard calls for the utilization of algebraic hand calculations, scale modeling, or computational fire modeling to determine the smoke control requirements.  Algebraic hand calculations are the most often utilized approach by mechanical engineers designing smoke control systems, however fire protection engineers (FPE’s) utilize computational fire modeling to optimize the calculation process.  Computer fire modeling (and often coupled with an egress analysis) results in a significant reduction in the mechanical demand required by such systems.  In most instances the use of computer fire modeling, and specifically the validated and verified Fire Dynamics Simulator (FDS), results in over a 50% reduction in mechanical capacity for these systems.  This reduction has an effect across multiple trades, such as thus reducing the required makeup air (i.e. louvers, windows, or doors on openers).

Analysis of pressurized stairwells and elevator hoistways, as well as smoke control systems for protected corridors and egress paths, can be
performed utilizing algebraic equations or with a network model such as CONTAM.  CONTAM is a building airflow and contaminant dispersal model
developed by the National Institute of Standards and Technology (NIST). CONTAM analyses are an approved method for analyzing and sizing
smoke control systems as recognized by NFPA 92 (Standard on Smoke Control Systems), referenced by the International Building Code (IBC). 

CONTAM is a great approach to perform a complete analysis on the interactions between multiple smoke control systems operating in a
building; general rules of thumb and algebraic equations may not be appropriate once multiple systems are incorporated into a design.  CONTAM
is utilized for two main purposes; the first is to determine what specific smoke control system design will be appropriate to achieve the
intended design conditions for each system evaluated (i.e. ground floor lobbies, external vent, simple system). Once an appropriate method is
determined, final capacities of supply and exhaust fans and locations can be determined through an iterative modeling approach, taking into
account sensitivity evaluations such as variance in external temperatures, wind, and building construction.

A CONTAM model can greatly assist your design team by ensuring that all aspects of a smoke control system operate as intended and meet
design criteria. Effects that one system has on another, such as the difficulty in balancing stairwell pressurization with an elevator
pressurization system, can be accounted for in the model. In addition, further analysis can be conducted on atrium smoke control systems,
coupling results from a fire dynamics simulator (FDS) or other computational fluid dynamics (CFD) model into CONTAM to examine the
impact that this additional system could have on stair pressurization.

The Rational Analysis is the most important piece of the design of a smoke control system for a building.  Often overlooked, the Rational Analysis serves as the basis behind the design of the system or series of systems, including atrium smoke, stairwell pressurization systems, elevator pressurization systems, zoned floor smoke control systems, and other specific application situations such as guestroom and public exit passageways.  When your AHJ asks to see the Rational Analysis for your systems, don’t be burned; have a well-documented basis of design proving the performance of the system, and assist the mechanical engineer in their final design of such systems.