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Smoke Management
Smoke management is a term used to describe the methods implemented to passively or actively control the movement of smoke within the built environment in the interest of providing safety to occupants, fire fighters, and property. Smoke management methods include compartmentation, dilution, pressurization, airflow and buoyancy [Klote, Milke, et al. 2012]. CONTAM has been used to analyze many of these smoke management techniques. It has been used to simulate smoke movement in multizone facilities, to analyze the performance of smoke control systems including stairwell pressurization systems and to aid in the performance of tenability (occupant safety) analysis. Analysis of smoke management requires the consideration of the interaction of the many different building characteristics and driving forces that affect smoke movement.
CONTAM provides for the analysis of different scenarios given an established building geometry, especially when that building geometry is fairly complex. CONTAM is a valuable tool that can be very useful in designing and analyzing smoke management systems. Its use still requires the judgment of a skilled fire protection engineer familiar with smoke management design techniques such as outlined by Klote & Milke, et al. (2012). It is also important that the engineer is aware of the limitations of CONTAM in capturing the near-field smoke transport phenomenon such as buoyancy driven flows due to the heat of the fire [Ferriera 1998].
The following is a brief description of the different methods that are currently considered when designing smoke management systems. These systems can be implemented individually or in conjunction with one another.
Compartmentalization - Passive compartmentalization refers to the use of physical barriers to hinder the movement of smoke from the fire space into the non-fire spaces. These barriers include walls, partitions, floors, doors and smoke dampers.
Dilution - Dilution of smoke typically refers to the removal of smoke from non-fire spaces to maintain acceptable levels of gas or particulates within the non-fire spaces. As the name implies, this method relies on the provision of make-up air to dilute the smoke or combustion gases that infiltrate a non-fire space as the air from that space is exhausted.
Pressurization - Pressurization or smoke control refers to the use of mechanical ventilation systems (fans) to induce pressure differences across barriers having a relatively high resistance to airflow (i.e. small gaps) to control the movement of smoke between compartments. Stairwell and elevator shaft pressurization and zoned smoke control are typical implementations of the pressurization method.
Airflow - Smoke control by airflow is very similar to the pressurization method except that it typically refers to the flow of air through relatively large openings. This method is typically not implemented in buildings, but more commonly implemented for smoke control in transportation tunnels.
Buoyancy - Buoyancy refers to the venting of hot (buoyant) combustion gases through fan-powered and passive vents typically located in the ceiling of large, open spaces such as atria and covered shopping malls.
Following are applications for which CONTAM can be useful in the design and analysis of smoke management systems.
Stairwell Pressurization
Stairwell pressurization systems are typically designed to maintain the stairwell at a higher pressure than the adjacent spaces to prevent infiltration of smoke into the stairwell. Typically, these systems are designed to maintain this pressure difference across closed stairwell doors, however consideration is often given to the effects of open doors on this pressure relationship. There are several different features of stairwell pressurization systems that require consideration when designing and analyzing them including leakage characteristics of walls and doors, number and location of injection fans and compartmentation of stairwells. CONTAM provides the ability to analyze these features by providing a generalized approach to defining vertical building configurations, leakage paths and fan systems.
Stairwell shafts can be defined by creating a series of zones located above one another interconnected with airflow paths using the stairwell model provided by CONTAM. Each of the stairwell zones can then be connected to any adjacent zones using several leakage models provided by CONTAM. These leakage models include doors, orifices and crack descriptions. Several methods of providing airflow to the stairwell are also available including constant volume and mass flow airflow elements, a fan a performance curve element, and the simple air handling unit model. A duct system can even be implemented to distribute the air to different levels of the stairwell.
There are several features of CONTAM that are quite useful when analyzing stairwell pressurization systems. The level copy feature of CONTAM can save a lot of time when defining multiple building levels that are very similar in layout. This feature enables the detailed definition of a typical level that can then be duplicated and copied above or below any existing level. Modifications to the copied levels can then be performed as necessary. User-defined minimum and maximum pressure (or flow) limits can be associated with airflow paths. If the simulation results determine that these limits are exceeded, the flow path will be flagged on the SketchPad results display. Finally, a shaft report can be generated that shows the pressure drop, airflow rate and direction for two selected airflow paths on each floor of a vertical shaft in a graphical, easy to print report format. These features can be very useful in bringing potential areas of concern to the attention of the designer/analyst.
Zoned Smoke Control Systems
Much like stairwell pressurization systems, zoned smoke control requires the analysis of inter-zone airflows and pressure differences. CONTAM provides the ability to establish the zonal geometry required to analyze the pressure and airflow relationships between smoke and non-smoke zones. The detail used to represent a building can range from very simple representations of smoke control zones as single-room zones to complex multi-room zones. Further, CONTAM provides the ability to establish airflows to or from the required zones. Again, this can range from the more simple to complex approaches of using individual constant flow fan elements, simple air handling systems, or establishing a complete duct system. Having established a building geometry and air handling system, CONTAM can be used to investigate different fire scenarios and smoke control strategies.
Combined Systems
Some smoke management systems implement combinations of the previously mentioned methods. For example, stairwell pressurization and zoned smoke control could be implemented within the same building. This combination of smoke management methods adds a level of complexity to the analysis of the smoke management system as a whole due to the potential interaction that can take place between the systems. CONTAM can be quite useful in managing this complexity and providing insight into the interaction between systems.
Tenability Analysis
Another major aspect in the design of smoke management systems is tenability or maintaining conditions that provide for occupant (or equipment) safety during a fire. There are several different aspects of tenability including temperature, toxicity of and visibility through smoke. CONTAM can be useful in the analysis of tenability particularly with respect to toxicity and visibility [Ferriera 1998]. The contaminant analysis features of CONTAM can be used to establish smoke-related contaminants from which toxicity and visibility information can be gleaned.
References
- Klote, J.H., J.A. Milke, P.G. Turnbull, A. Kashef, and M.J. Ferreira, Handbook of smoke control engineering. 2012: American Society of Heating Refrigerating and Air-Conditioning Engineers.
- Ferreira, M.J., Analysis of Smoke Control System Design Using A Computer-based Airflow Analysis, in 1998 Pacific Rim Conference and Second International conference on Performance-based Codes and Fire Safety Design Methods. 1998: Maui, HI.
Contacts
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(301) 975-6459
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(301) 975-5860
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(301) 975-6445