Guidelines for Guiding Smoke

The National Fire Protection Assn’s. Technical Committee on Smoke Management Systems will meet in September to discuss proposals to NFPA 92B, Guide for Smoke Management Systems in Malls, Atria and Large Areas .

Among the topics of discussion is how to transform the guide, which provides design, operation and maintenance data for smoke management systems in large-volume spaces, into an actual standard.

At the center of any such discussion are the physical factors that determine how the system is constructed. “One of the biggest things with these types of systems is determining the size of [a potential] fire, because that essentially is what drives your system,” says Milosh Puchovsky, principal fire protection engineer with NFPA and staff liaison to the committee. “That and the height of the space or the highest occupied level.”

According to Puchovsky, the September meeting will also include discussions on the impact of sprinklers on smoke management in atria, as well as how to estimate heat release rates for fires. As part of ongoing testing and study of new fire prevention technologies, discussions on which new technologies should become standardized will also take place.

After the September meeting, the committee will be balloted and a draft of 92B will be available in January 2004. The revised edition is expected to be available in 2005.

Jeff Harper, P.E., engineering manager for fire engineering consultant Rolf Jensen & Associates, Chicago, is, no doubt, among those eager to learn what will be discussed at the meeting.

Though it isn’t clear whether the subject will be covered when the NFPA technical committee convenes next month, Harper feels that currently, the biggest issue in smoke management for atriums is determining if the plume correlations—mathematical equations used to describe the development of a fire plume—that form the basis of the International Building Code and NFPA 92B are still valid. Specifically in question is the balcony spill plume, the plume from a fire that originates beneath a balcony or similar structure and projects upward into a tall space.

“The balcony spill plume raises some questions because the calculation assumes that a line plume is developed as it spills past the balcony, and the calculation is based on entrainment from that type of plume,” Harper says. “However, there is research out there that indicates that sprinklers located beneath the balcony disrupt the smoke plume and may not permit the plume to develop properly.”

Harper also points out that ASHRAE recently started a project to evaluate the validity of the balcony spill plume.

Aside from current events, Harper makes suggestions on how to make atrium smoke exhaust systems more efficient, stressing that one of the key factors to success is addressing system needs early in the design process. Sufficient makeup air is also crucial. “You can’t take out what you don’t put in,” Harper says. “Oftentimes, these systems aren’t given full consideration until too late in the design. Telling an architect that you need 600 sq. ft. of opening to the outside at the base of the atrium for makeup air doesn’t go very well when the design phase is nearing completion.”

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