How Integration Elevates Safety
In an addressable fire alarm system, a uniquely addressed relay module is connected to a signaling line circuit (SLC), which is used instead of ancillary relays inside specific smoke detectors. In this case, the fire alarm technician simply programs each uniquely addressed relay module to follow the status of any number of system detectors installed in elevator lobbies, elevator machine rooms and elevator hoistways. This includes the use of heat detectors when shunt-trip breakers are utilized.
Because the fire alarm system is under the control of arriving firefighters, this requirement assures the safety of all concerned. This is especially helpful in large multiple-floor buildings, such as high-rises, where firefighters often take control of elevators to gain rapid access to upper floors where a fire may be raging.
The new NFPA 72, 2010 Edition also requires interaction between a fire alarm system and the elevator controls within the structure, which is designed to make elevator use during fires even safer than in the past.
According to Section 21.3.12, “Separate outputs from the fire alarm systems to the elevator controller(s) shall be provided to implement elevator Phase I Emergency Recall Operation in accordance with Section 2.27 of ANSI/ASME A17.1a/CSA B44a, Safety Code for Elevators and Escalators, as required in 21.3.12.1 through 21.3.12.3.”
According to Sections 21.3.12.1 and 21.3.12.2, there are two designated floors on which elevators are to be returned during a fire situation: Designated Level Recall and Alternate Level Recall. The purpose of this dual-floor approach involves the issue of the safest place to return people who may still be on an elevator during a fire.
Containing Smoke’s Reach
Another extremely important area related to system interface using relays involves the issue of smoke control. Toxic smoke is one of the most common causes of death in structural fires. Thus it is important electrical engineers (EEs), architects and fire alarm technicians make every attempt to prevent the spread of smoke outside those areas actively involved in a fire.
There are several aspects related to smoke control that must be addressed when fire alarm technicians install a code-compliant fire alarm system. Some of them include the automatic release of doors, damper closure, stairway pressurization, HVAC shutdown and more.
As Section 21.7.5 indicates, this effort usually starts with the interface of fire alarm and HVAC system equipment: “If the fire alarm control unit actuates the HVAC system for the purpose of smoke control, the automatic alarm initiating zones shall be coordinated with the smoke-control zones they actuate.”
This kind of association can be achieved using a bank of programmable relays or individual relay modules. Each one is programmed to follow the status of an initiating zone or partition (area) so that dampers can be closed, thus preventing the spread of smoke into unaffected areas.
Spot-type smoke detectors listed for door release service by a third-party testing/listing facility can also be used to control the spread of smoke. Here, fire doors installed between smoke compartments separated by code-compliant fire walls are released, or closed, when smoke is detected.
It’s common practice to use either electromagnetic (EM) door holders or door holder closers to maintain these fire doors in an open position. Smoke detectors installed within 5 feet of these doors can be used to detect smoke before it migrates into areas not yet affected by the smoke and heat generated in another section of the building.
Section 17.7.5.4.1 also allows area smoke detectors located within smoke compartments to be used in the same manner. They also can be used to close HVAC dampers and to trip other equipment for the purpose of preventing the spread of smoke between smoke compartments.
Where dampers are involved, the same addressable relay output modules can be used to close them on cue, thus choking off any smoke that might attempt to migrate from one smoke compar
tment to another. This approach is especially helpful when fire alarm technicians work in large high-rise and multiple-tenant buildings. In such settings, partial evacuation may be used as opposed to total building evacuation.
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