Designing passive and active fire protection systems

Fire protection engineers should consider the building's construction, fire suppression systems, and smoke control when designing active and passive fire protection systems. The International Building Code and NFPA standards provide guidance on passive and active fire protection systems.

12/29/2017


This article has been peer-reviewed.Learning objectives:

  • Understand active and passive fire protection systems along with select requirements from the International Building Code.
  • Learn important considerations when selecting and designing fire protection systems.

The design of fire protection systems should be project-specific, cohesive, and consider the building lifecycle from the design to construction and operation. Passive fire protection systems include structural fire resistance, compartmentation (fire-rated walls, floors), and protection of the openings through them (fire doors, fire dampers, firestop systems). Active fire protection systems include sprinkler systems, alternative automatic fire-extinguishing systems, standpipe systems, fire extinguishers, fire alarm and detection systems, emergency alarm systems, and smoke control systems.

Fire protection systems must meet the client’s goals. At a minimum, buildings must be code-compliant, but owners and developers will consider construction and operational costs, the construction schedule, quality, design excellence, property protection, business continuity, and sustainability goals when seeking out design solutions. Projects often have various end users including customers, tenants, staff, user groups, maintenance, and facilities teams who influence these factors.

Fire protection systems must be cohesive. The best-designed buildings have a fire strategy that guides the selection of passive and active fire protection measures in response to the particular hazards and objectives of that project. Each system must be designed to meet the client’s goals, the fire strategy, and the applicable codes. Fire protection systems have interdependencies with each other and with non-life safety systems. The design team must identify and understand these interdependencies and ensure that they are properly coordinated.

The design phase is just the beginning of the building lifecycle. Fire protection systems must be designed with the construction and operational phases of the building in mind. Constructibility, field conditions, and construction phasing are just a few of the items to consider before and during construction. Post-construction, the owner must then understand and meet their responsibilities for operating, inspecting, testing, and maintaining these systems over the life of the building.

Passive fire protection

 

Active fire protection

 

     Fire-resistant-rated construction (walls, floor/ceiling, roof, barrier, partition)

     Fire-resistance rating of structural members

     Fire-resistant joint systems

     Penetration firestopping

     Opening protectives (fire door or window assembly, fire shutter, fire-rated glazing)

     Duct and air transfer openings (combination fire/smoke damper, fire damper, smoke damper).

 

     Automatic sprinkler systems

     Alternative automatic fire-extinguishing systems

     Standpipe systems

     Portable fire extinguishers

     Fire alarm and detection systems

     Emergency alarm systems

     Smoke control systems.

 

Table 1: The elements of passive and active fire protection systems. Courtesy: Arup

Figure 1: The design of passive and active fire protection systems must mitigate the potential fire risk in a structure while still meeting the project-specific goals and challenges that may be beyond the minimum requirements of the code. All graphics courClient goals

Design professionals might assume that the construction cost is the top priority for their clients. In reality, clients typically have a range of goals and priorities.

Fire/life safety goals will include life safety, property protection, and business continuity. The importance of the latter two goals will depend on the project type and client. Property protection is critically important in a museum storage facility or a distribution facility. Business continuity is paramount in an air traffic control tower, a trading floor, or a data center. (See Figure 1)

Design excellence and quality are important for many clients. Clients increasingly want to enhance occupant well-being and comfort. This often happens with reduced compartmentation, increased openness, and interconnections between floors. The model building codes facilitate this through non-separated mixed use, access-stair/escalator-floor opening allowances, and atrium provisions. Traditionally considered passive systems, hold-open fire doors and specialty doors, such as fire shutters, with or without egress also may aid in these goals. Unlike truly passive systems, such as walls, these systems are interdependent on other systems including the fire alarm system.

Designing high-performance buildings to meet environmental goals is becoming the norm because of client-led sustainability programs, construction codes, or government-led climate change initiatives. Fire protection engineers can make smart decisions in the design and specification of fire/life safety systems to facilitate sustainability goals. For instance, a structural system using mass timber has a lower carbon footprint than steel, concrete, or masonry and can be sized to provide fire resistance without applied fireproofing or being encapsulated in gypsum.

The building envelope is a major area of focus in high- performance buildings that must also meet requirements for fire safety, such as combustibility, flame-spread performance, and floor-to-floor compartmentation. When selecting a clean agent system, NFPA 2001: Standard on Clean Agent Fire Extinguishing Systems requires consideration of the effects of the agent on the environment including its ozone-depletion potential (ODP) and global warming potential (GWP) as well as how well the agent minimizes the environmental effects of the fire itself. NFPA 2001 publishes the ODP and GWP values for each agent, allowing engineers to evaluate each product.

Figure 2: Example of select components in the “total architecture” approach, which is applied to the design of a fire alarm system. This graphic does not include aspects of coordination relative to owners, end users, and stakeholders. Construction cost is only one aspect of the lifecycle building cost. Active and passive fire protection systems have operational costs related to inspections, testing, and maintenance that must be considered. Ease of maintenance is also a consideration including equipment required and business interruption, such as the type of smoke/heat detection selected for a high-ceiling space. A question that should be asked is “What are the operational preferences and capabilities of the facilities and maintenance staff?” These are important considerations when selecting fire protection systems.

Reducing the construction schedule is often a high priority and ought to be considered when selecting fire protection systems. A simple example is the use of drop-in or preformed firestop systems as compared with field-applied firestopping. Using a gypsum or mineral fiberboard product for fireproofing may be more labor-intensive when compared with spray-applied fire-resistive material but can eliminate a wet trade, which can be advantageous in certain projects. Prefabricated modular construction is one area where it is critical to consider these trade-offs between the material cost, labor cost, and schedule.

Understanding code requirements

While considering client goals is important, code compliance is required on all projects so the project team must understand the requirements. The International Building Code (IBC) is the model code adopted in most jurisdictions in the U.S. and will form the basis of this overview.

Passive fire protection systems are mostly covered in Chapters 5, 6, and 7 of the IBC. The type of construction required is determined using the height/story/area tables in Chapter 5 for the proposed use groups as defined in Chapter 3. The structural materials (steel, concrete, masonry, heavy timber, metal/wood stud) considered by the project team will also factor into which construction type is selected when more than one type is permitted. For example, a building that is taller than 420 ft must be Type I-A noncombustible construction (3-hour columns, 2-hour floors, beams, bearing walls). However, a 5-story building has multiple options for construction type. The type selected will depend on the client goals outlined previously herein. Fully sprinklered buildings are permitted increased height and floor area over nonsprinklered buildings. This is an example of the trade-offs in the building code between active and passive systems.

The fire-resistance ratings of structural members for each construction type are outlined in Chapter 6. The IBC details various compliance methods for determining the fire resistance ratings in Chapter 7. The most common methods use previously tested fire-resistance rating designs such as in the UL Fire Resistance Directory or Intertek Certification Directory, prescriptive designs per IBC, Section 721, or calculated designs per IBC, Section 722. In the absence of existing tested systems appropriate to the project, the client may elect to have fire testing completed for their project-specific assemblies. The IBC also permits engineering analysis and alternative protection methods.

Separated and non-separated mixed-use approaches, incidental use, and accessory use can be explored in Chapter 5 to determine the compliance strategy for compartmentation. If the building is mixed-use, a non-separated-use approach reduces the number of walls requiring opening protectives and firestopping but may result in a higher construction type depending on the building size and use.

Chapter 5 provides required fire-resistance ratings for separated occupancies. Chapter 7 provides the detailed requirements for fire-resistant-rated construction (fire walls, fire/smoke barriers, fire/smoke partitions, and floors). Fire-resistant joint systems, penetration firestopping, opening protectives (fire door or window assembly, fire shutter, fire-rated glazing), and duct and air-transfer openings (combination fire/smoke damper, fire damper, smoke damper) are all covered in Chapter 7.

Unlike passive fire protection systems, active fire protection requires some form of action/response in order to achieve the life safety objective of detecting a fire, notifying the occupants/fire department, managing smoke, or controlling/suppressing the fire.

Chapter 9 of the IBC outlines requirements for automatic sprinkler systems, alternative automatic fire-extinguishing systems, standpipe systems, portable fire extinguishers, fire alarm and detection systems, emergency alarm systems, and smoke control systems as well as identifies where each system is required. Generally, the requirements of Chapter 9 are based on occupancy. However, specific building areas, hazards, and applications that require protection regardless of occupancy are also outlined. In most instances, the IBC and International Fire Code reference NFPA standards for design, installation, inspection, testing, and maintenance requirements of the active fire protection systems.

The IBC sets forth the minimum requirements, yet providing the code-minimum level of protection may not achieve all project goals. The design team and project stakeholders should consider the project goals to ensure that the fire protection systems are tailored to the project. Designers also should consider the requirements of the local authority having jurisdiction (AHJ), the client, and the insurer that may require fire protection systems exceeding the construction codes.

Throughout the IBC, numerous trade-offs are recognized by using active fire protection systems. In addition to the trade-off previously noted, another example of this is smoke-protected seating, defined by the IBC as, “seating served by means of egress that is not subject to smoke accumulation within or under a structure.” For smoke-protected seating, either a smoke control system complying with Section 909 of the IBC or natural ventilation meeting the performance criteria of the code is provided, and the trade-offs include:

Areas of refuge are not required (Section 1009.3).

  • Areas of refuge are not required (Section 1009.3).
  • Reduced aisle widths (Section 1029.6).
  • Extended travel distances and common paths of travel (Section 1029.7 and 1029.8).
  • Longer dead-end aisles (Section 1029.9.5).
  • Increased row-length limits for aisle accessways (Section 1029.12.2).

Note that the above is not a comprehensive review of the smoke-protected seating requirements; however, it identifies select requirements of Section 1029 of the IBC as related to trade-offs for providing active fire protection.

Performance-based design

Performance-based design can be an integral part of the overall fire strategy for a building, particularly where prescriptive design may not allow the client goals to be fully realized. The IBC allows for performance-based design in a variety of ways including the administrative provision in Section 104.11.

The structural fire-resistance rating can be determined by engineering analysis that compares a proposed design with a previously tested design per Section 703.3, or by advanced modeling methods per Section 104.11 of the IBC.

Engineering judgments are often required for fire-rated assemblies, penetration firestop systems, and fire-resistant joint systems, particularly to address unique design/field conditions that vary from tested systems but can be demonstrated to meet the performance requirements.

In older existing buildings, there may be limited—if any—documentation verifying that the passive fireproofing systems meet applicable fire-resistance ratings. In these cases, the fire protection engineer may need to refer to fireproofing-material resources to determine the likely fire rating, such as the International Existing Building Code.

For active systems, performance-based design also is an integral part of the design process.

Smoke control systems are designed using a rational analysis by a registered design professional per Chapter 909 of the IBC and NFPA 92: Standard for Smoke Control Systems. This may include calculations, computational modeling, or real-world testing.

Audibility and intelligibility of fire alarm audible-notification appliances including public address systems can be modeled to verify and optimize performance. The project team must have relevant fire protection and acoustic expertise to complete these simulations accurately.


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