Complex fire alarm system design and commissioning
Fire protection engineers should determine the level of complexity needed in a fire alarm system design based on the building size/type and design a system that meets code requirements accordingly.
- Learn about unique features associated with a complex fire alarm system.
- Understand that smoke detectors can provide earlier detection of a fire, providing additional egress time.
- Have a basic understanding of the commissioning process.
Fire detection and alarm systems can be complex or simple. The level of complexity is focused around what hazards require protection and what are the most effective means of providing protection and instructing people to evacuate a building, or portion thereof.
A fire alarm system monitoring a small 2-story office building is not going to have the same level of complexity as a multi-use, multimillion-square-foot resort complex. The office building has occupants who are generally familiar with the environment and would recognize horn/strobe notification appliances as an abnormal condition that would require attention, leading to evacuation. A large casino resort hotel gaming complex has different types of occupants, different hazards, and unique conditions that may require evacuating only portions of the building.
Basic fire alarm networks include simple inputs and outputs. Inputs may include smoke detectors, duct-type smoke detection, fire suppression waterflow detection, valve-tamper monitoring, and other monitoring devices depending on the hazards protected. Outputs may be limited to audible and visual notification appliances, or they may include more sophisticated equipment that interfaces with building elements like elevator recall, de-energizing or energizing fans, and opening/closing dampers and doors.
The inputs and outputs are wired back to a control panel that contains the programming that defines what inputs affect which outputs. Complex systems often require multiple control panels that are set up as subpanels to a main fire alarm control unit (FACU) that provides instruction for all the subpanels.
High-rise buildings represent common examples of complex fire alarm systems due to challenges associated with increased egress times, large occupant loads, access by first responders, and potential smoke movement. The International Building Code (IBC) and International Fire Code (IFC) provide special life safety requirements for buildings classified as high-rise structures to mitigate the special hazards. High-rise buildings may use fire-detection and alarm systems for monitoring and controlling multiple life safety systems.
It is important to note that the IBC and IFC dictate when and where fire alarm systems, initiating devices, and notification appliances are required, and NFPA 72: National Fire Alarm and Signaling Code outlines how the systems are designed/installed after the designer has determined they are required.
The IBC defines a high-rise building as a building with an occupied floor located more than 75 ft above the lowest level of fire department access. High-rise buildings require an automatic smoke-detection system, a fire department communication system, and an emergency voice/alarm communication system. There are unique exceptions for specific occupancies that can be found in 2018 IBC, Section 907.2.12 The IBC also requires smoke detectors to be provided in specific locations throughout high-rise buildings, such as elevator machine rooms and elevator lobbies. The intent for requiring smoke detectors is to detect a fire in the early stages of development, which will provide more time for occupants to evacuate and for firefighters to get on scene before the fire grows to a size that cannot be managed.
Voice evacuation and testing
Another high-rise building fire alarm design requirement is to provide an emergency voice/alarm communication (EVAC) system. EVAC systems allow for more specific messages to building occupants by relating the type of emergency and instructions on how to egress when required.
For example, if a fire occurs on the 5th floor of a high-rise building with 20 floors, the voice evacuation message may annunciate alarm messages to occupants on the 4th, 5th, and 6th floors that a fire has been reported in the building and direct the occupants to the nearest exit. Occupants on Floors 1 through 3 and 7 through 20 may not be notified on their floors because they are not at immediate risk. This allows occupants closest to the fire to evacuate safely, with minimal occupants using egress systems and potentially reduced egress time.
If an authority having jurisdiction (AHJ) does not prescribe how many floors receive a notification of an alarm, the designer may provide specific direction in the design documents. The AHJ may require all floors to be notified, only the floor in alarm to be notified, or a combination of floors local to the alarm (floor above and floor below, one floor below and two floors above, etc.).
Multiplex fire alarm systems allow for annunciating different messages at the same time in different zones, depending on which floor/zone they are located in relative to the emergency. Multiplex fire alarm systems also are important in complex buildings that use horizontal exits. A fire on one side of a horizontal exit may annunciate an alarm message while the message on the other side of a horizontal exit may annunciate an alert message.
In addition to multiplex messages noted above, messages can also tell occupants on non-evacuating floors to remain in place while the event is being investigated. Modern fire alarm systems have the ability to offer six to eight channels of distributed audio. The designer may coordinate with the AHJ to decide if this is a feature they would need to implement for the specific project. While most fire alarm system manufacturers have multiplex system capabilities, specific hardware and programming is required to implement this feature. Therefore, specifying a multiplex design should be incorporated early in the design process and coordinated with the AHJ and owner to determine which floors/zones will receive specific messages in the event of an alarm condition.
The intent of a voice evacuation system is to provide a clear message that can be understood by the occupants in the event of an emergency. The intent is not to provide a high-level volume that you would typically see for systems using horns or horn/strobes providing only an audible alarm, but rather a clear and audible message. NFPA 72, Section 18.4.10, provides requirements for voice evacuation systems.
At this time, quantitative measurements are not required by code; however, guidance is offered in Annex D of NFPA 72 on how to test for speech intelligibility if the AHJ requires that. NFPA 72 recognizes that some areas in the building are difficult to provide intelligibility to due to acoustics, typical construction materials used in the areas, and room sizes. Examples may include private bathrooms, shower rooms, saunas, mechanical/electrical rooms, elevator cars, or storage rooms. Concrete parking structures within megaresorts also prove to be difficult for speech intelligibility, and NFPA 72 allows designers to classify these types of spaces as acoustically unintelligible.
NFPA 72, Annex D, outlines the methods for measuring speech intelligibility via the speech transmission index (STI), which uses a STI-public address (STIPA) test signal. To measure STI, a signal is played through the emergency communication microphone, and a meter is used throughout occupiable areas in the building to measure the STI levels. Per Annex D, a test is considered acceptable when the average STI is 0.50 throughout the building. Few jurisdictions require testing a voice evacuation system in accordance with Annex D. The more common approach is for an inspector to witness a prerecorded message being played and determining if the message is easily understood.
NFPA 72-2016 recognizes that typical speaker and speaker/strobes manufactured by fire alarm companies do not provide a high level of intelligibility. Typical speaker/strobes used for fire alarm notification are good at providing audibility (sound power), but to achieve intelligibility, more speakers are typically required for spaces. This is an additional cost to the owner that often is not desirable. As such, NFPA 72 has added Section 184.108.40.206 to the 2016 edition that allows non-listed loudspeakers to be installed to achieve intelligibility where listed systems cannot achieve intelligibility. This allows designers some flexibility in their design to use higher-quality speakers to potentially reduce the overall number in the space.
Commissioning, integrated system testing
Commissioning and integrated systems testing is a very complex task that could be published in volumes rather than one section of one article. This provides only a basic overview of what goes into these processes; seek subject matter experts to coordinate and carry out the testing.
Fire alarm commissioning is a systematic process that provides documented confirmation that building systems function according to the intended design criteria. NFPA 3: Standard for Commissioning of Fire Protection and Life Safety Systems provides the requirements for the commissioning of active and passive fire protection and life safety systems and their interconnections with other building systems. NFPA 4: Standard for Integrated Fire Protection and Life Safety System Testing provides requirements for the testing of integrated fire protection and life safety systems.
Testing of integrated fire protection systems includes, but is not limited to:
- Confirming initiating devices, such as manual pull stations, smoke detectors, heat detectors, or waterflow detectors, actuate an audible alarm, indicate an alarm on the FACU, close doors on hold-opens, and open dampers used for smoke control where applicable.
- Confirming that tamper switches, duct smoke detectors, and fire pump status inputs indicate a supervisory condition on the FACU.
- Confirming notification appliances (horns, speakers, and/or strobes) activate when an initiating device in the zone being activated is in alarm.
- Confirming operation of the firefighters’ telephone communication system.
For complex systems, test scenarios should be set up and provided to all stakeholders during the commissioning process to confirm all trades are aware of the design intent and sign off on the testing approach. Depending on the building complexity, the commissioning process can require input from trades including fire protection, mechanical, electrical, and door hardware.
Because of this, it is critical to start the commissioning process as early in the design phase as possible to ensure all test scenarios are accurate and all systems are coordinated to perform the intended function. For example, actuation of a smoke detector in a high-rise hotel corridor would require the fire alarm system to signal an alarm, start stair-pressurization fans, and possibly release doors on magnetic hold-opens. This requires coordination from multiple buildings systems and would be verified through the commissioning process.
Although the terms are commonly used interchangeably, commissioning is not the same as an acceptance test. NFPA 3 defines an acceptance test as a “test performed on an individual system to verify compliance with approved design documents to verify installation in accordance with governing laws, regulations, codes, and standards.” As such, it does not consider how all systems in a building work together as a whole to provide the owner with the desired finished product. Commissioning is a crucial process to ensure the building performs as designed prior to opening.