Design aspects of mass notification systems
The design and implementation of a mass notification system requires a risk analysis to determine the needs and requirements
- Understand the codes associated with mass notification systems.
- Learn about how a risk analysis affects MNS designs.
- Explore design and testing aspects of speech intelligibility.
Mass notification systems provide life-saving information to building occupants. The 2019 edition of NFPA 72: National Fire Alarm and Signaling Code Section 24.5 covers in-building MNS, Section 24.6 covers wide-area MNS and Section 24.7 covers distributed recipient MNS. These systems can be described as layers with layer one consisting of in-building MNS, layer two being wide-area MNS, layer three being distributed recipient MNS and layer four including public systems such as TV, radio, social media, etc.
Designers, architects, facility owners and the authority having jurisdiction should understand the rules governing MNS and should be able to identify appropriate approaches and performance expectations.
MNS can help to improve the safety and security of an organization by providing alerts and real-time instruction during a crisis. MNS can provide alerts for the following types of notifications:
- General information.
- Child abduction.
- Active shooter.
- Hazardous material release or exposure.
- Hostage situation.
- Severe weather.
- Traffic warnings or accidents.
The design of an MNS can include three project design phases: phase one is the identification or evaluation phase where the need for and rules of, an MNS are determined. Phase two is the design phase in which the entire design team needs to work together to ensure a successful product. Phase three is the testing phase and is determined by the designer for acoustically distinguishable spaces.
Identification and evaluation: phase one
Early in the program or design phase, the design team needs to evaluate the project requirements, including the need for an MNS.
The following items must be considered when planning for an MNS:
- Conduct a risk analysis to verify the need for an MNS. The steps for conducting the risk analysis are defined in NFPA 72 Section A.24.3.12.
- Develop a plan for meeting the requirements of the associated systems to support the MNS. For existing installations, survey the client’s electrical, telecommunications, life safety and security systems to determine necessary changes to accommodate the MNS infrastructure requirements.
- Consider the cost of integrating life safety, security and communication systems to create an MNS system that is efficient in its operation.
- Verify if the operations and maintenance staff have the personnel to manage and maintain the MNS.
To manage the systems mentioned above, a software platform is commonly required to integrate the fire, access control, security voice communications, email and texting systems into one seamless user interface that will allow messages to be generated to occupants.
When the project is governed by the Department of Defense or similar federal systems, the Unified Facilities Criteria Section 4-021-01 Design and O&M: Mass Notification Systems may also apply. UFC Section 4-021-01 provides requirements for both wide-area MNS and individual building MNS. A wide-area MNS provides information and instruction in an exterior or outdoor environment. This can cover a few acres to several hundred acres and even many square miles. An individual building MNS is contained to the building interior spaces as well as the building perimeter.
For new private-sector projects, the need for an MNS will be determined upon completion of a security risk analysis as defined in the 2018 edition of NFPA 101: Life Safety Code Section 9.14 and in compliance with any of the adopted regulations or design standards. The need for a risk analysis is based on listed occupancies in NFPA 101, including high-rise, assembly, educational, business and mall occupancies with occupant loads greater than the defined threshold or other similar delineations.
A risk analysis may be required by other sections of code, such as the 2018 International Building Code Section 917, which requires a risk analysis for college and university campuses with occupant loads greater than 1,000 people (see Figure 1).
The sections within NFPA 101 and NFPA 72 are clear in that they do not expressly require an MNS for a facility or campus, but instead provide the owner with the information to make an informed decision. As is typical with code, when an MNS is provided, it must meet the requirements of NFPA 72.
System design: phase two
Once the need and governing rules for an MNS are determined, the entire design team has to work together to ensure a successful outcome. There are some required head-end components that will need to be coordinated with the floor plan to ensure adequate space is provided. This equipment includes a local operating console and the autonomous control unit that may be integrated into the fire alarm control unit.
Note that if the building requires a fire command center, the space associated with the FCC also should house the equipment associated with the MNS. Refer to Section 911 of the IBC for FCC requirements. The LOC and ACU should be located such that it is easily found and operated by the local fire department and similar responsible parties. Burying the LOC in an electrical room is not proper design practice because of the need to access the LOC for both emergency and nonemergency messages and alerts and the typical location of electrical rooms limit accessibility in a timely manner.
The ideal location for the LOC and ACU typically is near the main entrance and coordinated with the local fire and police departments during design. The risk analysis should identify if the LOC and ACU should be accessible to the general public. The discussion of where to place a secure room near the main entrance is one that should happen early in design due the operation and aesthetic impacts that can result. NFPA 72 Section 220.127.116.11 includes guidelines for the physical mounting heights and accessibility of the LOC.
The placement of the LOC and ACU may be coordinated with the fire department’s entrance point. A meeting with the local fire department should occur during design to coordinate the risk analysis, which will drive the discussion on both the location and quantity of LOCs as well as the types and locations of system initiation. The electrical requirements for the equipment will fall under the 2017 edition of NFPA 70: National Electrical Code Article 700 for emergency systems or Article 517 for life safety branch systems.
The distributed recipient MNS will have a database of names, phone numbers and email addresses as delivery methods. The MNS software must have a communications infrastructure with enough bandwidth to deliver thousands of messages. People and organizations can be notified of an emergency situation by voice broadcast, prerecorded phone calls, text messages, emails and social media. The MNS can be activated manually or it can be activated by fire alarm pull stations, smoke detectors, gas detectors or highly specialized systems that notify occupants about active shooter events.
The next step is to determine the areas that require coverage. The risk analysis will include the selection of required areas and zoning, as noted in NFPA Section 72 18.104.22.168. These areas are going to be very similar to the spaces identified in NFPA 72 for fire alarm notification appliances while taking the both risk analysis results and Architectural Barriers Act accessibility guidelines into consideration.
A simple guideline for visual notification is to assume that any space that could be occupied by someone who is hearing impaired should have coverage and the locations of devices should be readily visible at any point in an occupiable area. These areas include public or staff corridors, passageways, lounges, meeting rooms, break rooms, work rooms, waiting areas and treatment, testing or examination rooms. Care should be taken to ensure that obstacles like such as bookshelves, carts or furniture do not hinder the ability for the notification appliance to provide required coverage. The designer should coordinate carefully with the architectural floor plan, the furniture drawings and the owner’s equipment plans to prevent the need to move devices after substantial completion.
In some buildings there may be two separate visual appliances: one white/clear and the other amber. The white/clear notification appliance indicates a fire alarm event while the amber notification appliance indicates a mass notification event.
The 2019 edition of NFPA 72 Section 24.5.17 allows for a clear notification appliance be used for both fire alarm and MNS, but does have requirement for labeling with “alert” in lieu of “fire.” This section is clear that the MNS does not need to be the same equipment or systems as the fire alarm system. Exceptions to this arrangement exist in the UFC 4-021 4-3.4.2 for specific military branch installations.
Visual device spacing and location requirements can be found in NFPA 72 Section 18.5 for public mode installations. Specific installations may allow for private mode requirements, which are outlined in NFPA 72 Section 18.6. These requirements are listed in tables but can be calculated using the prescriptive methods to achieve 0.0375 lumens per square foot.
Visual devices may be wall- or ceiling-mounted. When using a ceiling mount, the mounting height will affect the coverage area of each device. When using ceiling-mounted devices, further coordination with the architectural ceiling plan is required to ensure that bulkheads, soffits or other ceiling undulations do not inhibit coverage. Simply put, if you cannot see a visual notification appliance when standing at any location in a required coverage area, the device is not providing the required coverage.
Lastly, the intensity of the device — or how bright it is — is measured in candelas and should be correctly selected during design to ensure the battery capacity calculations and power supply sections are accurate. It is the responsibility of the designer to identify the proper intensity of each device and the same rules apply for both fire alarm and MNS visual appliances.
An added form of visual notification is textual signage. The textual signs provide information to occupants who may not be able to hear the audible message. The location of these signs are defined in the applicable codes and are typically at exterior doors, exit enclosures and interior public areas. NFPA 72 Section 24.5.20 also allows for video systems and video displays to be used for MNS information.
The audible requirements for a MNS are another area that requires careful coordination between the design team, the owner and the AHJ in concert with the risk analysis results. The AHJ may be considered local, state and federal agencies that can include historical or similar reviewers. NFPA 72 Section 18.4.11 identifies that the designer is responsible for determining the areas where intelligibility is required.
The success of an audible notification system is strongly dependent on the acoustical performance of the building finishes. The reverberation time of a space is defined as the amount of time it takes sound to decay by 60 decibels. Also known as RT60 (refer to ASTM E2235: Standard Test Method for Determination of Decay Rates for Use in Sound Insulation Test Methods or ISO 3382: Acoustics), the reverberation time is usually defined in octave bands of 63, 125, 250, 500, 1,000, 2,000, 4,000 and 8,000 hertz.
Each of the building surfaces and acoustical treatments will have specific effects on the RT60 of each octave band and designers need to carefully choose surfaces and treatments that prevent one or more bands from being too high. A list of acceptable RT60 ranges can be found in the U.S. Green Building Council Reference Guide for Interior Design and Construction, version 4, Indoor Environmental Quality Credit for Acoustic Performance – Table 2: Reverberation Time Requirements.
Typically, it is prudent to maintain an RT60 below 1.0 seconds within the 500-, 1,000- and 2,000-hertz octave bands to minimize detrimental echoes and acoustical interference in the vocal range of the speaker system (see Figure 2).
Controlling the reverberation of the building interior is an effort that requires specific coordination between the MNS designer and the architect to identify rooms that will require acoustical treatments to ensure intelligibility requirements can be met. Spaces without acoustical ceiling tiles or carpeting are likely to require some treatment if the volume is large (typically greater than 1,000 square feet).
The placement and quantity of speakers will be affected by the acoustical environment, requiring the designer to calculate multiple simulations to determine the ideal layout. Acoustical calculations can be performed using manual calculations or with commercially available software. Preliminary calculations should be done on any rooms that are large, complex or unique. Designers also must control the background noise levels, which are commonly the result of the building HVAC system. Recommended noise levels and HVAC design strategies are well-defined in the 2019 ASHRAE Handbook: HVAC Applications Chapter 49: Noise and Vibration Control
NFPA 72 Section 22.214.171.124 defines these types of spaces as acoustically distinguishable spaces. It is important to identify any acoustical requirements early in design to evaluate and include the costs and aesthetic impacts of the treatments.
The primary strategy for ensuring that the voice notification system will be intelligible is to design a system that ensures building occupants either hear only one speaker at a time or hear multiple speakers at nearly the same time while minimizing reflections. Therefore, speakers located on the walls can struggle with meeting intelligibility requirements when multiple speakers are required. Ceiling speakers tend to alleviate the concerns mentioned above because listeners will naturally transition between speakers in a way that results in similar distance and level. When considering that a MNS relays voice messages, the design will have similar goals as paging systems.
Once the system is installed, verification is required to ensure the system meets the requirements for intelligibility. NFPA 72 Annex D explains that.
Testing: phase 3
All of the MNS components and systems should be tested for functionality and communication. For brevity, this article will focus on the intelligibly aspects of testing. NFPA 1: Fire Code includes MNS inspection and testing forms. The recommendations for intelligibility testing are in NFPA 72 Annex D.4 and are presented as informational and not requirements. These recommendations include the speech intelligibility equipment setup, including how to correctly set the testing equipment volume and audio levels.
The intelligibility system testing levels chosen by the designer will vary based on occupied versus unoccupied testing environments (see Figure 4). While testing with the building occupied is ideal for verification of real-world conditions, it is not desirable to wait until the building is occupied to perform the testing due to the disruption of both the testing and any adjustments.
Testing will be performed using the speech transmission index methods described. Some projects may use the common intelligibly scale in lieu of STI, but it is easy to convert one from the other using the following equation: CIS = 1 + log10 (STI). See Figure 3 for correlating the two scales.
The full list of testing information is listed in NFPA 72 Annex D.7.3.2 and includes project and building information as well as acoustical testing locations, conditions and results. As noted in NFPA 72 Section 18.4.11, NFPA recognizes that not all spaces require intelligibility. As stated in NFPA 72 Annex D3.6.1, smaller areas with favorable acoustics can be omitted from testing given a representative sample or calculation.
When the location is acoustically challenging and intelligibility over the entire area is not feasible, the design should ensure intelligibility near exits or other defined areas where occupants are most likely to be located. The primary challenge for the design team is defining the ADS and Annex D 3.6 provides guidelines for designers to assist with choosing which areas to calculate and test. Areas determined to be of high importance in the risk analysis also should be taken into consideration for both calculation and testing.