Notice to Designers for Smoke Control Systems

Questions about Georgia Codes and Standards

Notice to Designers for Smoke Control Systems

Postby Blackstone on Thu Nov 20, 2008 10:15 pm

Smoke Control System Shop Drawing Submittals

The following information is provided as a guide to assist those submitting Smoke Control System Shop Drawings for Review and Approval:

1. 2003 IFC, Sections 909.10 and 909.4.4 requires the exhaust system (fan, motor, etc.) to consider the effects of the fire on the system. The exhaust fan must be rated to withstand the predicted maximum temperature that the system could experience, and where the fire could be located directly below the unit, the temperature must be evaluated and a means provided to ensure the fire shall not adversely affect the unit(s) (e.g. 3000ºF rated unit). Ensure exhaust fans are UL Listed (ZAXH) for Smoke Control Systems ~ all detection and control components are required to be UL Listed (UUKL or UUKL2) for Smoke Control Systems (UL 864) per 2003 IFC, Section 909.12.

2. Automatic exhaust louvers (natural supply) in combination with automatically operated doors (mechanical supply) are acceptable make-up air sources. Indicate the mounting height of all makeup air device(s) and provide data sheets on the natural and mechanical system equipment for review.

3. Provide a detailed layout (1/4 scale or larger) of the Fire Command Center for review and approval per 2003 IFC, Section 509.1 requirements. Layout shall indicate all applicable components listed in items 1 thru 15 of this section, complete with make, model, etc. Ensure equipment layout has been coordinated with local Fire Official prior to submitting to this office for review and approval. The Fire Command Center and Generator Rooms must be a minimum of a 1-hour Fire Barrier per 2003 IFC, Sections 509.1 and 909.11.

4. 2003 IFC, Section 909.18.8.2 requires those performing the Smoke Control System Acceptance Test to have expertise in: Fire Protection Engineering; Mechanical Engineering; and Certification as Air Balancers. Special inspections are required per Section 909.18.8.1 such as during construction and near completion before the acceptance test.

5. All wiring for the Smoke Control System (including wiring from FACP to Smoke Control Panel) shall be enclosed in continuous raceways per 2003 IFC, Section 909.12.1. Fire Alarm System wiring shall comply with 2002 NAC Article 760 requirements.

6. Smoke Control exhaust fans used for dual purposes shall ensure the Smoke Control function will override any auxiliary uses (such as warm weather ventilation) during emergency conditions.

7. The Smoke Control System Design should include addressing axisymmetric fire plumes, and as applicable, window or balcony spill plumes and plumes in contact with walls. Atriums of unconventional design (long and narrow, multiple levels with relatively small opening to floor ratios, unique geometric configurations, etc.) should use the NFPA 92B and 2003 IFC empirical formulas only as a starting point for preliminary calculations for estimation (see more info at: ), and then use a Computational Fluid Dynamic (CFD) Fire Models (e.g. Fire Dynamic Simulator ~ FDS) used for the actual final design layout, fan sizing, etc.

8. Section 909.11 requires a secondary power supply (to fans, make-up air devices, etc.). Provide information indicating compliance with this section.

9. Section 909.12 indicates detection and control system requirements. Provide information (diagram, matrix, etc.) on interface to Fire Alarm System, Smoke Control Panel, etc., and include layout of detection devices, and layout of exhaust/makeup air equipment.

10. 2003 International Fire Code (IFC), Section 909.16 requires a Smoke Control Panel complying with Sections 909.16.1 through 909.16.3 to be located in a Fire Command Center complying with 2003 IFC, Section 509.

11. All submitted drawings shall be on an unalterable medium (i.e. no vellum, mylar, pencil, adhesive applied details, etc.). Include a Transmittal Form with all submittals, in addition to two full sets of Smoke Control System Shop Drawings, a copy of the approved sealed engineering analysis (drawings, calculations, etc.) complete with a copy of its comment sheet, and two copies of any data sheets (fans, controls, etc.).

Smoke Control Design Considerations

The belief that NFPA 92B, Section saying that the balcony spill plume formula is only valid for non-sprinklered spaces and should not be used is not quite what this section is trying to get across! The section is indicating the formula is derived from non-sprinklered spaces true enough (even 1/10th scale experiments!), however since it’s accuracy was based on non-sprinklered spaces, when used in sprinklered spaces, the dynamics of the sprinklers should be taken into consideration in some cases – this in addition to the geometry involved (location of fire, lintels, draft-stops, etc.).

Worst case is the sprinkler system has a valve shut, MIC has reduced the pipe cross section to effectively nothing, etc., and the smoke control is not affected by sprinklers (a CFD fire model such as the Fire Dynamics Simulator will also show that even in an unsprinklered space, the geometry itself can cause bizarre curling vortexes ~ see for more about how these NFPA 92B formulas are supposed to be only a starting place, and in situations involving complex atria, fire modeling should be the next step).

Conversely, the sprinklers work and you get bizarre curling vortexes which impinge on different levels, etc. due to the interaction with the water droplets, cooling, etc. - or perhaps even a smaller fire due to suppression system controlling the fire which the smoke control system will easily deal with.

The ICC people in the 2006 version appear to have just ducked-out of the controversy by removing the formula’s all together and defaulting to whatever NFPA 92B says – they have not said balcony spill calculations are not required for sprinklered spaces. The 2004 supplement to the 2003 IFC had originally just removed the requirement, but with all the controversy of the balcony spill formula the next edition just removed ALL the formulas (axisymmetric, window, etc.) and just left it up to NFPA…

As far as valid reasons not to require a balcony spill calculation - a fairly narrow balcony that would not appreciably affect the plume (such as a running track around the top of a gym, etc.) would be one such case for omitting the calculations, just as omitting the window spill calculations if all openings are few and relatively small, etc. Sure, not all the formulas are always relevant since atriums differ – some have no windows or balconies.

Perhaps the balcony spill plume calculations are a bit overly conservative, but until the ASHRAE/IRC research is done, it is better than just ignoring the phenomena. If the balcony spill plume calculations are indicating a smoke production rate that seems exorbitant, one could try using CFD fire modeling as an alternative which would be the more prudent approach than just saying the calculations are not required at all.

The smoke development analysis in each of the design approaches must be justified using algebraic calculations for preliminary calculations only, unless approved by the Authority Having Jurisdiction for atria with simple geometry’s and a single floor openings (to limit use of equations outside their validation), and detailed design calculations using (to require modeling for other than very simple atria) zone, scale, computational fluid dynamics (CFD), and compartment fire models. Computational fluid dynamics (CFD) models must be used for atria designs with complex geometry and/or multiple floor openings when required by the Authority Having Jurisdiction (to permit AHJ to judge complexity of atria and require a state of the art simulation type model).
We find consulations, we learn tricks with which we deceive ourselves, but the essential thing - the way - we do not find. Listen to the river.

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