Smoke Barrier. A continuous membrane, either vertical or horizontal, such as a wall, floor, or ceiling assembly that is designed and constructed to restrict the movement of smoke. See also NFPA 101, Life Safety Code, Chapter 6 for additional guidance.

Smoke Compartment. A smoke compartment is a space within a building enclosed by smoke barriers on all sides, including the top and bottom. In the provision of smoke compartments utilizing the outside walls or the roof of a building, it is not intended that outside walls or roofs or any openings therein be capable of resisting the passage of smoke.

Smoke Control. A system that utilizes fans to produce pressure differences so as to manage smoke movement.

Fire Smoke Damper. A device within the air distribution system to control the movement of smoke. Smoke dampers are subjected to various pressure differentials, are exposed to elevated temperatures, and can be required to open or close against mechanically induced airflow. Some such devices are listed in UL Building Materials Directory under the category "Leakage Rated Dampers (OOYZ)."

Smoke control systems. Often found in high-rise buildings, covered malls, airports, atriums, and high value properties such as computer rooms, telephone central offices, and semiconductor fabrication plants. Smoke control systems are used wherever additional time may be required to allow occupants to evacuate a building, such as hospitals, assisted-care facilities, malls, airports, and high-rise building.

Smoke detectors. Used to detect and prevent smoke spread by initiating control of fans, dampers, and doors.

Weekly UUKL Self-test. The weekly self-test consists of the smoke control system automatically commanding the associated function to operate and expecting, within a specified time, that the associated proof sensor will operate. A valid proof sensor operation does not have to be annunciated. However, the lack of an expected proof sensor operation should produce an audible trouble signal and indicate the specific device which did not operate.

Flash-over. The explosive migration of hot gases and fire, usually in corridors not containing Fire Doors/Barriers.

Passive Fire Protection. A passive fire protection system is one which is an integral part of the building layout and materials of construction, such as partitions to confine the fire, a stairway to assist rapid evacuation, or spray-on fire proofing to increase the fire resistance of a load-bearing steel structure.

Active Fire Protection. Systems are designed to come into play only when a fire is present and require activation through a combination of sensors or mechanical means.

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 and Milke 1992]. CONTAM is a computer program uniquely suited for the analysis of zoned smoke control systems, stairwell pressurization systems, and elevator pressurization systems. Data input includes floor plan representation, zone properties, phantom zones, building leakage, airflow paths, air handling systems, supply points, return points, and weather data. 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.

It is important to realize that the main strength of CONTAM lies in its ability to provide 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 [1992]. 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.

Compartmentation - Passive compartmentation 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 some of the above 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.

Of course pressurizing the stairwells is useless if the building occupants can not reach them. It is critical to pressurize the egress corridors also to provide the means for occupants to gain access to the pressurized stairwells. In high-rise residential, commercial and Hotel blocks this consists of all corridors leading from occupied units to stairwells etc.

Zoned Smoke Control Systems

Much like stairwell pressurization systems, zoned smoke control requires the analysis of interzonal 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, CONTAMW 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.

Smoke-control systems are designed to control smoke during a fire incident in order to contain danger and allow the building to be safely evacuated. Until recently, smoke control has been managed by the building automation system (BAS). But the trend over the last few years has been to shift that control to the fire-protection system. That shift has created new fire-alarm functions and performance requirements, of which facility managers are often unaware.

Requirements and categories

NFPA Standards 92A and 92B cover all requirements for all types of smoke-control applications. BAS manufacturers also produce resources that explain the various applications. Smoke-control systems are broken into two major categories: Dedicated and Non-Dedicated Systems.

Dedicated systems are those that don't perform any other functions. The fans and dampers are not used for everyday ventilation, only for smoke-control events. These are often found in stairwells and elevator shafts. Typically these areas are pressurized to prevent the spread of smoke through exit passageways in the building. In atria, these are typically used for smoke exhaust in order to control the smoke layer.

Non-dedicated systems provide HVAC in the building every day, but are captured by the smoke-control system in the event of a fire. There are numerous types of non-dedicated systems, based upon the HVAC design. For example, a building designed with single exhaust and pressurization fans to cover multiple floors or areas is a different type than one with fans for each floor. But the basic principles are the same: The smoke-control system captures the fans and dampers in the event of a fire, in order to control smoke.

The front-end of every smoke-control system is the Firefighters' Smoke Control Station. This includes annunciation of every fan, damper and other component of the system, typically through labeled LEDs. It also provides manual overrides for every fan and damper to be used by the fire department. It must be in an accessible location.

The two major authorities on smoke control - Underwriters Laboratory (UL) and the Uniform Building Code - require that this station include a graphic representation of the building. This typically includes the LEDs for annunciating device status placed over an elevation view of the building. Inputs to the system come from the basic fire initiating devices: smoke detectors and/or manual stations that initiate a smoke-control sequence. These devices are connected to the fire-alarm system.

At the other end of the system are the fans and dampers to be controlled. These are typically connected to some portion of the BAS. The challenge is to take the information from the initiating devices to the fans and dampers, and process the incoming information, either in the fire or HVAC system, to meet the specified control methodology of turning the correct fans and dampers on and off at the right times.

The next step is the interface that exchanges information between the fire and BAS. There is always a requirement for positive feedback at the smoke-control station, indicating that the specific fan or damper has reached the intended state.

The BAS provider or the fire-protection-system provider must assume a lead role in making the smoke-control operation work properly. Both provide hardware for the operation; either can provide the Firefighter's Smoke Control Station and process the logic necessary to control devices. Usually the same company provides the station and processes the logic.

There are two ways to get information from the fire system to the BAS system. The first is for the fire system to monitor all inputs, process the smoke-control logic, then operate fans and dampers through relays that capture the device controllers. This means that the fire system is in control. The other is for the fire system to communicate fire events and conditions to the BAS. That system will then process the logic that operates the proper fans and dampers.

Smoke-control strategy

At the time of new construction, the engineer for the project will develop a smoke-control strategy for the building. This will be in the form of a document often called a rational analysis or Smoke Control Report. It will include at least three key items:

Sequence of operation - A step-by-step definition of how the fans and dampers should operate. Typical sequences of events for different applications can usually be found in the manufacturers' smoke-control application guides. The engineer may also specify a sequence of operation restoring the entire system to its normal operations after a fire event has ended.

Detail - An explanation of the action caused by the various fire-alarm initiating devices. For instance, manual stations will very often start purge or pressurization sequences in stairwells, atria, etc. Smoke detectors may initiate a floor-by-floor sequence designed to contain the smoke at the floor of incidence.

Feedback - The process of providing detail about how quickly fans and dampers should operate during a fire. This will be specified in terms of actual operation and/or feedback at the Firefighters' Smoke Control Station. The Uniform Building Code also includes specific time limits for both operation and feedback. The engineer should specify what the system should do if feedback is not received in the allotted time.

Be aware that the system response-time element can place a large burden on the operation of the controlling system and is often the most difficult criteria to meet. Typically, fire-alarm systems process alarms as a priority while smoke-control operations are treated as status events. The process of turning on an LED to annunciate the completion of a device's change in status is usually at the lowest priority level in the system.

If the fire system is managing too many other functions, smoke-control operations may not occur within the required time. Consult the system manufacturer for recommendations on how to best configure a system to meet the response requirements in your facility.

Atrium Smoke Control

The most critical of all the technical issues to be solved in a successful atrium design is Life Safety because atrium buildings break with orthodox concepts of Safety. Life Safety design for any building is difficult. It involves more than a provision for emergency egress, it requires attention to who will be using the building and what they will be doing. Consideration must be given to communication, the protection of escape routes, and temporary areas of refuge allowing reasonable time for the building occupants to reach safety.

Because of its critical nature both NFPA 101 "The Life Safety Code" and The International Building Code have extensive code provisions for Atriums. Since the code provisions are extensive we will not recite them here but refer any design team to an exhaustive review of the requirements. Both NFPA and the IBC give significant explanatory material to atriums in their Life Safety Code Handbook and IBC commentary respectively. While similar they are not identical. A significant difference is that the IBC is prescriptive and arbitrarily limits the number of floors that maybe open to the atrium to three, where the Life Safety Code is more performance oriented and will allow the number of floors open to the atriums without enclosure be based upon the results of the required engineering analysis.

One of the basic premises of atrium requirements is that an engineered smoke control system combined with an automatic fire sprinkler system that is properly supervised provide an adequate alternative to the fire resistance rating of a shaft enclosure. It is also recognized that some form of boundary is required to assist the smoke control system in containing smoke to just the atrium area.

Both the Life Safety Code and IBC require that the atrium space be separated from adjacent areas by fire barriers having a fire rating of 1 hour or equivalent. Both codes accept adjacent spaces to be separated by properly constructed glass walls where automatic sprinklers have been installed to protect the glass. The sprinklers are to be located so as to wet the entire surface of the glass.

The development of most code provisions has largely been a response to specific fires and the desire to prevent recurrences. For example, in recent times many present code provisions were responses to the Coconut Grove Night Club fire, the Chicago school fire, and the MGM Grand fire. Conventional doctrine dictates that to achieve Fire and Life Safety that fires must be kept as small as possible and the effect of fire limited to as small an area as possible. This philosophy has resulted in conventional building configurations employing compartmentalized construction of fire rated floors and fire rated walls.

While atrium design breaks with conventional building configurations Fire / Life Safety in atrium buildings is comprised of the same three elements as in conventional buildings—means of escape, smoke control, and fire control. Means of escape, emergency egress is a fundamental plan issue and must be integral with the circulation concept of the building. Emergency egress must be incorporated from day one. Smoke control strategies are also fundamental and must be part of the initial ventilation concepts. Fire control and fire fighting provisions must also be integrated in to the original concepts.

The basic concept of means of egress planning is that occupants can move away from a fire and reach a protected means of egress by their own unaided efforts. This route must remain tenable throughout the evacuation process. A complicating element that must be addressed is that in an emergency people tend to use the route they are familiar with. Occupants of office buildings can be trained by fire drills but visitors will only know the way they came in. Means of egress protected exit stairs should be on familiar routes and in intuitive locations and signed very clearly. Mean of egress should not be unduly exposed to potential hazards. (Refer NFPA 101) The Life Safety Code being more performance based requires that an engineering analysis be performed to demonstrate that smoke will be managed for the time needed to evacuate the building. To accomplish this, the analysis must prove that the smoke layer interface will be maintained above the highest unprotected opening to adjacent spaces, or 72" above the highest floor level of exit access open to the atrium for a time equal to 1.5 times the calculated egress time or 20 minutes, whichever is greater. For a protect-in-place occupancy, such as Healthcare, the evacuation time is considered to be infinite, which means that the smoke control performance criteria must be maintained indefinitely.

The fire record has shown that smoke is the primary threat to life from fire in buildings. Smoke is the most rapidly developed threat. Proper smoke control in an atrium building is an absolute must. Smoke control systems that are integral to the buildings ventilation systems are preferred over stand alone systems. Integral systems are more reliable because their components are constantly being monitored and maintained. (Refer NFPA 92B Guide for Smoke Management Systems in Malls, Atria, and large areas.) NFPA 92B, quantifies the physics associated with atrium smoke control and presents methodologies for system design in an understandable and useful format. The guidelines of NFPA 92B allow the system designer to design a system and prepare associated documentation to access for adequacy in meeting the performance criteria.

The basic nature of fire and smoke must be well understood by the design team in order to incorporate smoke control in to the physical configuration of the atrium from the earliest schematic designs. Well designed smoke control cannot be added to a design, it must be integral to the design.

Effective smoke control depends upon rapid control of fire size to limit smoke quantities to manageable volumes. Fundamental to effective smoke / fire control is early detection and suppression. Smoke and or fire detection systems must be designed to identify and locate a fire early in its development. The fire prevention and smoke removal strategies for the atrium will vary dependent on the location of the fire and the configuration of the atrium.

Large volumes and high ceilings significantly complicate and possibly delay early smoke and heat detection. Systems that can detect the smoke near the occupied floor levels and close to the potential fire sources are best. Smoke detectors should be placed in ceilings in spaces surrounding the atrium but located within the atrium enclosure. These include balconies, seating alcoves, corridors, lobbies, and other spaces that have typical ceiling heights. To detect smoke in the high ceiling area, detectors should be located near the atrium floor to detect smoke prior to rising and potentially dissipating in the large volume. If the space is tall enough, smoke will cool and begin to descend back to the floor level, without reaching the upper ceiling level. Beam detectors are one potential solution to detecting smoke at lower levels of the atrium. If used, the location of beam detectors transmitters and receivers must be carefully chosen to allow the proper coverage, and to allow easy access for adjustment, testing, and periodic maintenance. Smoke and or heat detectors should also always be placed at the highest ceiling level as a precaution in case the other detection systems did not activate. The figure below in a highly simplified form represents many of the items that must be considered in the smoke control system in an atrium.

Early suppression of a fire is essential to effectively limit the amount of smoke to manageable levels. Automatic sprinklers are the most effective means of fire suppression appropriate to atriums. The fundamental nature of atria presents challenges to the effective use of automatic sprinklers. In atriums with high ceiling heights, typical sprinkler designs provide marginal fire extinguishing capabilities and may actually be detrimental to the smoke removal system. Water from sprinkler heads located greater than 75 feet above the fire source may break up into a fine mist and evaporate before reaching the fire source. The evaporation of sprinkler water may cool the smoke and reduce the effectiveness of smoke removal systems, which were designed to pull the smoke from the top of the enclosure.

A qualified life safety consultant or fire protection engineer (FPE) involved early in the atrium design is the best source of potential fire detection and prevention system selection options. The FPE is knowledgeable in all of the atrium code issues. The codes and standards that address smoke control systems for atria are based on similar research and fundamental fire size and smoke generation models. ASHRAE 1999 Applications, Chapter 51 provides a broad design basis for smoke management that provides general directions to the designer. NFPA 92 is more specific and provides a set of calculations that can be performed by the FPE to determine the quantity of exhaust necessary to evacuate the smoke generated by the largest anticipated fire size. The calculations cannot anticipate all of the aspects that are unique to the atrium under design, and therefore should only be used for the most simple of atrium configurations. For all atria, and especially complex or tall atria, a qualified life safety consultant should be employed to assist in determining the smoke control system parameters. Currently the most comprehensive method of determining complex smoke management criteria is with computer fire modeling. (Reference ASHRAE 1999 Applications, Chapter 51.12) In many instances the results of the computer modeling will result in lower exhaust quantities being required, and therefore lowering initial project costs. The model allows multiple fire origins to be evaluated, and the resulting smoke removal system needs to be adequate for all anticipated fire origin location.

Computer modeling and visualization are important tools for understanding the processes of fire behavior. Fire models range in complexity from simple correlations for predicting quantities such as flame heights or flow velocities to moderately complex zone fire models for predicting time-dependent smoke layer temperatures and heights. Zone fire models' calculations can run on today's computers within minutes because they solve only four differential equations per room. Zone models approximate the entire upper layer with just one temperature. This approximation works remarkably well but breaks down for complicated flows or geometries. For such cases, computational fluid dynamics (CFD) techniques are required.

Even when the actual exhaust quantities were determined by use of a computer fire model, smoke management systems shall be designed in adherence to all other requirements of NFPA 92. Requirements such as the use of direct drive equipment in lieu of belt drive, protection of control wiring, emergency power, and the design and installation of a fireman's control panel to allow manual operation of the smoke removal equipment is mandatory. (Reference NFPA 92)

NIST Evaluates Firefighting Tactics in High-Rise Test

March 28, 2008 // Published as a news service by IHS

National Institute of Standards and Technology (NIST) fire protection engineers turned an abandoned New York City brick high-rise into a seven-story fire laboratory to better understand the fast-moving spread of wind-driven flames, smoke and toxic gases through corridors and stairways of burning buildings.

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The experiments on Governors Island, conducted in partnership with the Fire Department of New York City (FDNY) and New York's Polytechnic University, examined the effectiveness of firefighting tactics, such as the use of positive pressure ventilation fans, wind control devices and hose streams to control or suppress deadly heat and smoke from the wind-driven fires.

Between 1985 and 2002, 1,600 civilians died and more than 20,000 people were injured in approximately 385,000 high-rise building fires in the U.S., according to the National Fire Protection Association (NFPA).

Due to temperature differences between the outside and inside of a building on fire, open doors and broken windows far from the actual site of the fire can dramatically increase the movement of hot gases and smoke.

Wind-driven flames, heat and smoke with temperatures exceeding 1500 F can speed across entire floors and around corridors without warning. Smoke and heat entering stairwells often can block the evacuation of occupants and can hinder firefighting operations, experts said.

To develop an understanding of the wind-driven fires and measure the impact of the firefighting tactics, NIST researchers placed cameras, as well as temperature and pressure sensors throughout the building. From a safe ground floor monitoring post, the researchers monitored the progress of intentionally set fires raging through the apartments and public corridors. They recorded the effects of opening or closing doors and windows, both near and far from the blaze.

Positive pressure ventilation fans, prototype wind control devices and prototype high-rise fire suppression nozzles, which were developed by FDNY, all had a positive impact on controlling the effects of wind-driven fires.

Research findings from the Governors Island experiments are expected to help improve fire service guidelines for combating high-rise fires, as well as enhance firefighter safety, fire ground operations and use of equipment. NIST expects to issue a report on the high-rise experiments by November 2008.

The U.S. Department of Homeland Security's (DHS) Federal Emergency Management Agency (FEMA) funded the Governors Island tests under its Assistance to Firefighters grant program.

Source: National Institute of Standards and Technology (NIST).

Documents

An overview of Smoke Control Research

SFPE Engineering Guide

Small Atrium Smoke Control

Smoke Movement in a Building via Elevator Shafts

Fire Smoke Damper Test Sheet

Computer Program for the Analysis of Smoke Control Systems

References

1.     Uniform Building Code^®, International Conference of Building Officials, Whittier, CA, 1991.

2.     International Building Code^®, International Code Council, Washington, DC, 2006.

3.    The 2000 Life Safety Code (LSC)-National Fire Protection Association (NFPA) 101.

4.     NFPA 92A, Recommended Practice for Smoke Control Systems, National Fire Protection Association, Quincy, MA, 1988.

5.     NFPA 92B, Guide for Smoke Management Systems in Malls, Atria, and Large Areas, National Fire Protection Association, Quincy, MA, 1991.

6.     Klote, J., and Milke, J., Design of Smoke Management Systems, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, 1992.

7.     Walton, D., "ASET-B: A Room Fire Program for Personal Computers," NBSIR 85-3144-1, National Bureau of Standards, Gaithersburg, MD, 1985.

8.     Peacock, R., et al, "CFAST: The Consolidated Model of Fire Growth and Smoke Transport," NISTTN 1299, National Institute of Standards and Technology, Gaithersburg, MD, 1993.

9.     Walton, G., and Emmerich, S., "CONTAM93: A Multizone Airflow and Contaminant Dispersal Model With a Graphic User Interface," National Institute of Standards and Technology,     Gaithersburg, MD, 1994.

10.     McGrattan, K., and Forney, G., "Fire Dynamics Simulator: User's Manual," NISTIR 6469, National Institute of Standards and Technology, Gaithersburg, MD, 2000.

11.  NFPA 92B, Standard for Smoke Management Systems in Malls, Atria, and Large Areas, National Fire Protection Association, Quincy, MA, 2005.