WHY SHOULD I CONSIDER INCLUDING SMOKE CONTROL IN MY BUILDING?
A smoke-control system can help reduce the migration of smoke during a fire, allowing occupants more time to exit the building, aiding firefighting and search-and-rescue efforts, and minimizing smoke damage.
Because of code requirements, most integrated buildings have a fire-alarm system. Many also have a programmable building-control system. Between the two, wiring and devices for monitoring fire conditions and controlling fans, dampers, and other mechanical equipment are in place. Extending integration capabilities to allow a building-control system to respond to signals from a fire-alarm system eliminates the need to duplicate control programming or install cutouts and overrides. Further, it enables the building-control system to respond in a fire-appropriate manner (see When the Normal Response Is Wrong).
Depending on the size of a building and the occupancy classification of the spaces within, one may not have a choice about including smoke control. The International Building Code (IBC), for instance, requires smoke control in stairwells of buildings more than 75 ft above grade, in atria of three or more stories, in covered malls, in assembly seating areas, and in underground areas more than 30 ft below the lowest exit. Other codes have different requirements.
WHICH SYSTEM SHOULD I USE TO PERFORM SMOKE CONTROL?
Building codes specify building types and occupancy classifications that are to include smoke control. They also specify what smoke-control systems are to accomplish. But, contrary to popular belief, they do not specify the system to be used to perform smoke control. The IBC, for instance, requires that smoke-control systems "be equipped with a control unit complying with UL 864 (Underwriters Laboratories' Standard for Control Units and Accessories for Fire Alarm Systems) and listed as smoke-control equipment." Other codes are less specific, including only boilerplate text requiring that equipment be listed for its intended purpose.
Even though both fire-alarm and smoke-control systems are listed under UL 864, their listings are not interchangeable. Fire-alarm systems are listed for their ability to detect and annunciate fire conditions, while smoke-control systems are listed for their ability, to perform specified control logic and adhere to specific priorities of operation. Systems with both abilities can be listed for both fire-alarm and smoke-control use.
If your fire-alarm system is UL-listed for smoke control, your building already has suitable control panels. However, you likely will need to add control circuits and associated cutout and override devices to energize and de-energize fans and dampers during smoke-control operations.
If your building-control system is listed for smoke control, control panels allowing you to use existing control wiring to energize and de-energize fans and dampers for smoke control already are in place. With fire-alarm-system conditions already being monitored, all that is needed is enhancement of the control program of the building-control system so that it will override its normal operation and respond appropriately to information from the fire-alarm system.
If both your fire-alarm system and building-control system are listed for smoke control, either can be used for smoke control. The one that has more control wiring for fans and dampers already in place likely will prove to be the more cost-effective system to use for smoke control.
WILL I NEED A LOT OF EXTRA CONTROL LOGIC?
The amount of control logic needed is determined by the type and complexity of the smoke-control strategy to be employed. A non-compensating stair-pressurization system requires little control logic, while a zoned smoke-control system in a building with many compartments requires much.
Where the possibility of activating a smoke-control system from multiple sources exists, building codes and standards specify a hierarchy of responses. NFPA (National Fire Protection Association) 92A, Standard for Smoke-Control Systems Utilizing Barriers and Pressure Differences, states that the operational mode activated in response to the first automatic input should be maintained, even if additional automatic activation signals are received. Where manual operation is allowed, the last manually activated operational mode takes precedence over any automatically activated response. The operational mode selected at the firefighter's smoke-control station (FSCS), meanwhile, takes priority over all other modes of activation.
Any system listed for smoke-control applications is capable of implementing control logic to energize and de-energize appropriate systems while conforming to the required activation hierarchy. Some systems meet these requirements using program logic arranged so that responses to particular activation signals are carried out unless an overriding condition is present. Other systems utilize a priority structure to ensure that only the highest-priority response is executed.
Both the IBC and NFPA 92A require smoke-control systems to verify that equipment activates as intended within allotted times (time is allowed for fans to spin up or down and for dampers to travel to intended positions). Smoke-control systems must indicate a fault condition if a device fails to activate or does not remain active for the intended period of time. While the ability to provide end-to-end verification is resident in some systems listed for smoke-control applications, others require extensive programming, which adds to installation cost.
DO I HAVE TO CONTROL ALL OF MY TERMINAL BOXES?
Control of terminal boxes is one of the least understood--and most intimidating--aspects of smoke control. Once its place in an overall smoke-control strategy is understood, however, it often ceases to be an issue.
What must be understood first is that smoke control occurs at zone boundaries. Building codes already require smoke dampers where ductwork penetrates a smoke barrier (i.e., at the zone boundaries), whether a smoke-control system is present or not. These smoke dampers must be controlled to meet smoke-control objectives.
Terminal boxes are not a substitute for smoke dampers because smoke dampers have a leakage rating in accordance with UL 555S, Standard for Smoke Dampers, while control dampers installed in terminal boxes do not. Building codes and standards require smoke dampers to be installed in the plane or within a few inches of a smoke barrier using approved mounting methods. Installation far downstream of a smoke barrier, such as at a terminal box, would not be an approved configuration.
Terminal boxes, therefore, are considered to be located within smoke-control zones. What goes on inside a smoke-control zone may or may not be part of an overall smoke-control strategy. NFPA 92A addresses terminal-box controls, saying: "Examples of auxiliary functions that can be useful, but are not required, are the opening and closing of terminal boxes while pressurizing or exhausting a smoke zone. These functions are considered auxiliary if the desired state is achieved without these functions. These functions can, however, help to achieve the desired state more readily."
If a terminal box has a minimum-airflow setting, perhaps for comfort or indoor-air-quality reasons, the damper always will be partially open, and desired zone pressurization can be achieved without controlling the terminal box. According to NFPA 92A, the terminal box, then, is considered auxiliary, not a required part of the smoke-control system. This means neither control of the terminal box during smoke-control operations nor UL 864 listing of the terminal-box controllers is required. Although no additional control logic is required to add smoke control in this situation, designers often specify that terminal boxes be commanded to a fully open position during smoke control to achieve intended results more readily.
CAN I USE ETHERNET WIRING THAT ALREADY IS INSTALLED IN MY BUILDING?
Of the many building-control systems utilizing Ethernet wiring, a small number are UL-listed for smoke control. Nearly all of these listed systems, however, are restricted in their use of Ethernet for smoke-control applications.
Requirements for the use of Ethernet wiring in smoke-control systems are relatively easy to understand, but often difficult to meet. The first requirement is that smoke-control signals not travel through equipment not listed for smoke control. This means that smoke-control data for monitoring or control cannot pass through an Ethernet router or server on its way to its intended destination, unless that router or server also is listed for smoke control. Few, if any, such devices exist, however.
The second requirement is that control panels used for smoke control be isolated from the rest of a network's data traffic. This limits a smoke-control system to the use of a dedicated subnet and broadcast domain separated from the rest of the building's Ethernet devices by a router. (The router does not have to be listed for smoke control because smoke-control data do not pass through it.)
The simplest way to comply with these requirements is with a separate Ethernet network used by the smoke-control system only. In smaller installations, this may be an acceptable configuration, even though a separate Ethernet cable is required. However, it generally is not what building owners have in mind when purchasing a system that communicates over Ethernet.
In medium-sized installations, smoke-control systems can utilize Ethernet wiring if switches connecting the wiring to various Ethernet-compatible devices are listed for fire or smoke control. A few such switches exist. Building-control panels that do not participate in smoke control can be connected to Ethernet using standard Ethernet switches.
In larger installations in which routers or servers are necessary to pass data from one part of a building-control system to another, smoke control over Ethernet often is impractical because connecting all of the smoke-control equipment without passing data through devices not listed for smoke control is impossible. One exception might be a campus setting in which routers or servers pass data between buildings, but smoke-control signals stay within the buildings and, thus, do not pass through equipment not listed for smoke control.
WHAT OTHER PITFALLS SHOULD I WATCH OUT FOR?
One of the biggest pitfalls--from the standpoint of both installation cost and maintenance cost--is splitting controls across systems. Unless operation of the overall integrated system is specified in detail, fire-alarm specifications and building-control specifications may overlap. If they do, both the fire-alarm system and the building-control system will contain portions of the control logic for smoke control, adding unnecessary complexity and hardware costs.
A common example of overlapping specifications sees a fire-alarm system shutting down a fan when smoke is detected and a building-control system activating the appropriate smoke-control strategy. For both systems to comply with their portion of the specification, the fire-alarm system must include a control circuit and control logic to open a series contact to de-energize the fall, while the building-control system must include a control circuit and control logic to close a parallel contact to restart the fan. Similar redundancies exist when a fire-alarm system is used to activate fans for smoke control: The fire-alarm system must include a control circuit and control logic to close a parallel contact to restart a fan shut down by a building-control system. By utilizing the capabilities of an integrated system and placing the control logic for both normal building controls and smoke control into one system, no additional control circuits are required, and the cost and confusion of additional controls is avoided.
Buildings that employ integration to allow monitoring of fire-alarm and building-control systems from a single location already may contain much of the control equipment and control wiring needed to perform smoke control. If one or more of the systems in a building is listed for smoke control, adding cutout and override hardware becomes unnecessary. With the addition of control logic to prioritize the operation of mechanical equipment, the existing capabilities of systems can be utilized to add smoke-control functionality at minimal additional cost.
When the Normal Response Is Wrong
Building-control-system operation is governed by an algorithm devised to provide occupant comfort by maintaining temperature, humidity, and airflow within specified ranges. If, for instance, measured temperature is too high or too low, a system will attempt to correct the condition by cooling or heating the space. Building-control systems perform such functions well, but, without additional information, have no way of determining whether their normal response is the correct response at a particular time.
For instance, during normal operations, a building-control system will attempt to lower high space temperature by blowing cold air into the space. During a fire, however, this action will fan flames and cause smoke to migrate to other parts of the building. With information from the fire-alarm system integrated into the logic of the building-control system, however, the building-control algorithm could determine that the building is not operating under normal conditions and initiate a more appropriate response.
PAUL G. TURNBULL
Siemens Building Technologies Inc.
Buffalo Grove, Ill.
Paul G. Turnball is a principal applications engineer for Siemens Building Technologies Inc., specializing in the integration of fire, security, and lighting-control systems with building controls. He is active on the smoke-management committees of the NFPA and ASHRAE. He can be contacted at email@example.com.